[PATCH 0/3] ext4: Add support for mounted updates to the superblock via an ioctl

[PATCH 0/3] ext4: Add support for mounted updates to the superblock via an ioctl

[Theodore Ts'o]

This patch series enables a future version of tune2fs to be able to
modify certain parts of the ext4 superblock without to write to the
block device.

The first patch fixes a potential buffer overrun caused by a
maliciously moified superblock.  The second patch adds support for
32-bit uid and gid's which can have access to the reserved blocks pool.
The last patch adds the ioctl's which will be used by tune2fs.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
Theodore Ts'o (3):
      ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
      ext4: add support for 32-bit default reserved uid and gid values
      ext4: implemet new ioctls to set and get superblock parameters

 fs/ext4/ext4.h            |  16 ++++-
 fs/ext4/ioctl.c           | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 fs/ext4/super.c           |  25 +++-----
 include/uapi/linux/ext4.h |  75 ++++++++++++++++++++++
 4 files changed, 348 insertions(+), 24 deletions(-)
---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250830-tune2fs-3376beb72403

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>

[PATCH 0/3] ext4: Add support for mounted updates to the superblock via an ioctl

[Theodore Ts'o via B4 Relay]

This patch series enables a future version of tune2fs to be able to
modify certain parts of the ext4 superblock without to write to the
block device.

The first patch fixes a potential buffer overrun caused by a
maliciously moified superblock.  The second patch adds support for
32-bit uid and gid's which can have access to the reserved blocks pool.
The last patch adds the ioctl's which will be used by tune2fs.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
Theodore Ts'o (3):
      ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()
      ext4: add support for 32-bit default reserved uid and gid values
      ext4: implemet new ioctls to set and get superblock parameters

 fs/ext4/ext4.h            |  16 ++++-
 fs/ext4/ioctl.c           | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 fs/ext4/super.c           |  25 +++-----
 include/uapi/linux/ext4.h |  75 ++++++++++++++++++++++
 4 files changed, 348 insertions(+), 24 deletions(-)
---
base-commit: b320789d6883cc00ac78ce83bccbfe7ed58afcf0
change-id: 20250830-tune2fs-3376beb72403

Best regards,
-- 
Theodore Ts'o <tytso@mit.edu>

[PATCH 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

[Theodore Ts'o]

Unlike other strings in the ext4 superblock, we rely on tune2fs to
make sure s_mount_opts is NUL terminated.  Harden
parse_apply_sb_mount_options() by treating s_mount_opts as a potential
__nonstring.

Cc: stable@vger.kernel.org
Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/super.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
 					struct ext4_fs_context *m_ctx)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	char *s_mount_opts = NULL;
+	char s_mount_opts[65];
 	struct ext4_fs_context *s_ctx = NULL;
 	struct fs_context *fc = NULL;
 	int ret = -ENOMEM;
@@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
 	if (!sbi->s_es->s_mount_opts[0])
 		return 0;
 
-	s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
-				sizeof(sbi->s_es->s_mount_opts),
-				GFP_KERNEL);
-	if (!s_mount_opts)
-		return ret;
+	strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
 
 	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
 	if (!fc)
-		goto out_free;
+		return -ENOMEM;
 
 	s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
 	if (!s_ctx)
@@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
 	ret = 0;
 
 out_free:
-	if (fc) {
-		ext4_fc_free(fc);
-		kfree(fc);
-	}
-	kfree(s_mount_opts);
+	ext4_fc_free(fc);
+	kfree(fc);
 	return ret;
 }
 

-- 
2.51.0

[PATCH 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

[Theodore Ts'o via B4 Relay]

From: Theodore Ts'o <tytso@mit.edu>

Unlike other strings in the ext4 superblock, we rely on tune2fs to
make sure s_mount_opts is NUL terminated.  Harden
parse_apply_sb_mount_options() by treating s_mount_opts as a potential
__nonstring.

Cc: stable@vger.kernel.org
Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/super.c | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
 					struct ext4_fs_context *m_ctx)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	char *s_mount_opts = NULL;
+	char s_mount_opts[65];
 	struct ext4_fs_context *s_ctx = NULL;
 	struct fs_context *fc = NULL;
 	int ret = -ENOMEM;
@@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
 	if (!sbi->s_es->s_mount_opts[0])
 		return 0;
 
-	s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
-				sizeof(sbi->s_es->s_mount_opts),
-				GFP_KERNEL);
-	if (!s_mount_opts)
-		return ret;
+	strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
 
 	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
 	if (!fc)
-		goto out_free;
+		return -ENOMEM;
 
 	s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
 	if (!s_ctx)
@@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
 	ret = 0;
 
 out_free:
-	if (fc) {
-		ext4_fc_free(fc);
-		kfree(fc);
-	}
-	kfree(s_mount_opts);
+	ext4_fc_free(fc);
+	kfree(fc);
 	return ret;
 }
 

-- 
2.51.0

Re: [PATCH 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

[Darrick J. Wong]

On Mon, Sep 08, 2025 at 11:15:48PM -0400, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
> 
> Unlike other strings in the ext4 superblock, we rely on tune2fs to
> make sure s_mount_opts is NUL terminated.  Harden
> parse_apply_sb_mount_options() by treating s_mount_opts as a potential
> __nonstring.

Uh.... does that mean that a filesystem with exactly 64 bytes worth of
mount option string (and no trailing null) could do something malicious?

My guess is that s_usr_quota_inum mostly saves us, but a nastycrafted
filesystem with more than 2^24 inodes could cause an out of bounds
memory access?  But that most likely will just fail the mount option
parser anyway?

--D

> 
> Cc: stable@vger.kernel.org
> Fixes: 8b67f04ab9de ("ext4: Add mount options in superblock")
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
>  fs/ext4/super.c | 17 +++++------------
>  1 file changed, 5 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 699c15db28a82f26809bf68533454a242596f0fd..94c98446c84f9a4614971d246ca7f001de610a8a 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2460,7 +2460,7 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
>  					struct ext4_fs_context *m_ctx)
>  {
>  	struct ext4_sb_info *sbi = EXT4_SB(sb);
> -	char *s_mount_opts = NULL;
> +	char s_mount_opts[65];
>  	struct ext4_fs_context *s_ctx = NULL;
>  	struct fs_context *fc = NULL;
>  	int ret = -ENOMEM;
> @@ -2468,15 +2468,11 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
>  	if (!sbi->s_es->s_mount_opts[0])
>  		return 0;
>  
> -	s_mount_opts = kstrndup(sbi->s_es->s_mount_opts,
> -				sizeof(sbi->s_es->s_mount_opts),
> -				GFP_KERNEL);
> -	if (!s_mount_opts)
> -		return ret;
> +	strscpy_pad(s_mount_opts, sbi->s_es->s_mount_opts);
>  
>  	fc = kzalloc(sizeof(struct fs_context), GFP_KERNEL);
>  	if (!fc)
> -		goto out_free;
> +		return -ENOMEM;
>  
>  	s_ctx = kzalloc(sizeof(struct ext4_fs_context), GFP_KERNEL);
>  	if (!s_ctx)
> @@ -2508,11 +2504,8 @@ static int parse_apply_sb_mount_options(struct super_block *sb,
>  	ret = 0;
>  
>  out_free:
> -	if (fc) {
> -		ext4_fc_free(fc);
> -		kfree(fc);
> -	}
> -	kfree(s_mount_opts);
> +	ext4_fc_free(fc);
> +	kfree(fc);
>  	return ret;
>  }
>  
> 
> -- 
> 2.51.0
> 
> 
> 

Re: [PATCH 1/3] ext4: avoid potential buffer over-read in parse_apply_sb_mount_options()

[Theodore Ts'o]

On Thu, Sep 11, 2025 at 03:27:00PM -0700, Darrick J. Wong wrote:
> On Mon, Sep 08, 2025 at 11:15:48PM -0400, Theodore Ts'o via B4 Relay wrote:
> > From: Theodore Ts'o <tytso@mit.edu>
> > 
> > Unlike other strings in the ext4 superblock, we rely on tune2fs to
> > make sure s_mount_opts is NUL terminated.  Harden
> > parse_apply_sb_mount_options() by treating s_mount_opts as a potential
> > __nonstring.
> 
> Uh.... does that mean that a filesystem with exactly 64 bytes worth of
> mount option string (and no trailing null) could do something malicious?

Maybe.... I'm surprised syzkaller hasn't managed to create a
maliciously fuzzed file system along these lines.

This was one of the things that I found while I was poking about in
code that I hadn't examined in years.  And I guess the kernel
hardening folks have been looking for strndup() as a deprecated
interface, but apparently they haven't targetted kstrndup() yet.

> My guess is that s_usr_quota_inum mostly saves us, but a nastycrafted
> filesystem with more than 2^24 inodes could cause an out of bounds
> memory access?  But that most likely will just fail the mount option
> parser anyway?

Actually, s_usr_quota_inum won't help, because s_mount_opts is copied
into allocated memory using kstrndup().  So the buffer overrun is
going to be in the allocated memory buffer, and since parse_options()
uses strsep() it could potentially modify an adajacent string/buffer
by replacing ',' and '=' bytes with NUL characters.  I'll leave to
security engineers to see if they can turn it into a usuable exploit,
although I've always said that mounting untrusted file systems isn't a
wise thing for a paranoid system administrator to do/allow, which is
why I'm a big fan of your fuse2fs work.  :-)

						- Ted

[PATCH 2/3] ext4: add support for 32-bit default reserved uid and gid values

[Theodore Ts'o]

Support for specifying the default user id and group id that is
allowed to use the reserved block space was added way back when Linux
only supported 16-bit uid's and gid's.  (Yeah, that long ago.)  It's
not a commonly used feature, but let's add support for 32-bit user and
group id's.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/ext4.h  | 16 +++++++++++++++-
 fs/ext4/super.c |  8 ++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1442,7 +1442,9 @@ struct ext4_super_block {
 	__le16  s_encoding;		/* Filename charset encoding */
 	__le16  s_encoding_flags;	/* Filename charset encoding flags */
 	__le32  s_orphan_file_inum;	/* Inode for tracking orphan inodes */
-	__le32	s_reserved[94];		/* Padding to the end of the block */
+	__le16	s_def_resuid_hi;
+	__le16	s_def_resgid_hi;
+	__le32	s_reserved[93];		/* Padding to the end of the block */
 	__le32	s_checksum;		/* crc32c(superblock) */
 };
 
@@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 		 ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
 }
 
+static inline int ext4_get_resuid(struct ext4_super_block *es)
+{
+	return(le16_to_cpu(es->s_def_resuid) |
+	       (le16_to_cpu(es->s_def_resuid_hi) << 16));
+}
+
+static inline int ext4_get_resgid(struct ext4_super_block *es)
+{
+	return(le16_to_cpu(es->s_def_resgid) |
+	       (le16_to_cpu(es->s_def_resgid_hi) << 16));
+}
+
 /*
  * Returns: sbi->field[index]
  * Used to access an array element from the following sbi fields which require
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 94c98446c84f9a4614971d246ca7f001de610a8a..0256c8f7c6cee2b8d9295f2fa9a7acd904382e83 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2951,11 +2951,11 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 	}
 
 	if (nodefs || !uid_eq(sbi->s_resuid, make_kuid(&init_user_ns, EXT4_DEF_RESUID)) ||
-	    le16_to_cpu(es->s_def_resuid) != EXT4_DEF_RESUID)
+	    ext4_get_resuid(es) != EXT4_DEF_RESUID)
 		SEQ_OPTS_PRINT("resuid=%u",
 				from_kuid_munged(&init_user_ns, sbi->s_resuid));
 	if (nodefs || !gid_eq(sbi->s_resgid, make_kgid(&init_user_ns, EXT4_DEF_RESGID)) ||
-	    le16_to_cpu(es->s_def_resgid) != EXT4_DEF_RESGID)
+	    ext4_get_resgid(es) != EXT4_DEF_RESGID)
 		SEQ_OPTS_PRINT("resgid=%u",
 				from_kgid_munged(&init_user_ns, sbi->s_resgid));
 	def_errors = nodefs ? -1 : le16_to_cpu(es->s_errors);
@@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 
 	ext4_set_def_opts(sb, es);
 
-	sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
-	sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
+	sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
+	sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
 	sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
 	sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
 	sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;

-- 
2.51.0

[PATCH 2/3] ext4: add support for 32-bit default reserved uid and gid values

[Theodore Ts'o via B4 Relay]

From: Theodore Ts'o <tytso@mit.edu>

Support for specifying the default user id and group id that is
allowed to use the reserved block space was added way back when Linux
only supported 16-bit uid's and gid's.  (Yeah, that long ago.)  It's
not a commonly used feature, but let's add support for 32-bit user and
group id's.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/ext4.h  | 16 +++++++++++++++-
 fs/ext4/super.c |  8 ++++----
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1442,7 +1442,9 @@ struct ext4_super_block {
 	__le16  s_encoding;		/* Filename charset encoding */
 	__le16  s_encoding_flags;	/* Filename charset encoding flags */
 	__le32  s_orphan_file_inum;	/* Inode for tracking orphan inodes */
-	__le32	s_reserved[94];		/* Padding to the end of the block */
+	__le16	s_def_resuid_hi;
+	__le16	s_def_resgid_hi;
+	__le32	s_reserved[93];		/* Padding to the end of the block */
 	__le32	s_checksum;		/* crc32c(superblock) */
 };
 
@@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 		 ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
 }
 
+static inline int ext4_get_resuid(struct ext4_super_block *es)
+{
+	return(le16_to_cpu(es->s_def_resuid) |
+	       (le16_to_cpu(es->s_def_resuid_hi) << 16));
+}
+
+static inline int ext4_get_resgid(struct ext4_super_block *es)
+{
+	return(le16_to_cpu(es->s_def_resgid) |
+	       (le16_to_cpu(es->s_def_resgid_hi) << 16));
+}
+
 /*
  * Returns: sbi->field[index]
  * Used to access an array element from the following sbi fields which require
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 94c98446c84f9a4614971d246ca7f001de610a8a..0256c8f7c6cee2b8d9295f2fa9a7acd904382e83 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2951,11 +2951,11 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
 	}
 
 	if (nodefs || !uid_eq(sbi->s_resuid, make_kuid(&init_user_ns, EXT4_DEF_RESUID)) ||
-	    le16_to_cpu(es->s_def_resuid) != EXT4_DEF_RESUID)
+	    ext4_get_resuid(es) != EXT4_DEF_RESUID)
 		SEQ_OPTS_PRINT("resuid=%u",
 				from_kuid_munged(&init_user_ns, sbi->s_resuid));
 	if (nodefs || !gid_eq(sbi->s_resgid, make_kgid(&init_user_ns, EXT4_DEF_RESGID)) ||
-	    le16_to_cpu(es->s_def_resgid) != EXT4_DEF_RESGID)
+	    ext4_get_resgid(es) != EXT4_DEF_RESGID)
 		SEQ_OPTS_PRINT("resgid=%u",
 				from_kgid_munged(&init_user_ns, sbi->s_resgid));
 	def_errors = nodefs ? -1 : le16_to_cpu(es->s_errors);
@@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 
 	ext4_set_def_opts(sb, es);
 
-	sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
-	sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
+	sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
+	sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
 	sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
 	sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
 	sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;

-- 
2.51.0

Re: [PATCH 2/3] ext4: add support for 32-bit default reserved uid and gid values

[Darrick J. Wong]

On Mon, Sep 08, 2025 at 11:15:49PM -0400, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
> 
> Support for specifying the default user id and group id that is
> allowed to use the reserved block space was added way back when Linux
> only supported 16-bit uid's and gid's.  (Yeah, that long ago.)  It's
> not a commonly used feature, but let's add support for 32-bit user and
> group id's.
> 
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
>  fs/ext4/ext4.h  | 16 +++++++++++++++-
>  fs/ext4/super.c |  8 ++++----
>  2 files changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 01a6e2de7fc3ef0e20b039d3200b9c9bd656f59f..4bfcd5f0c74fda30db4009ee28fbee00a2f6b76f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1442,7 +1442,9 @@ struct ext4_super_block {
>  	__le16  s_encoding;		/* Filename charset encoding */
>  	__le16  s_encoding_flags;	/* Filename charset encoding flags */
>  	__le32  s_orphan_file_inum;	/* Inode for tracking orphan inodes */
> -	__le32	s_reserved[94];		/* Padding to the end of the block */
> +	__le16	s_def_resuid_hi;
> +	__le16	s_def_resgid_hi;
> +	__le32	s_reserved[93];		/* Padding to the end of the block */

Does anything actually check that s_reserved is zero?  I couldn't find
any:

$ git grep -w s_reserved fs/ext4 fs/ext2
fs/ext2/ext2.h:480:     __u32   s_reserved[190];        /* Padding to the end of the block */
fs/ext4/ext4.h:1445:    __le32  s_reserved[94];         /* Padding to the end of the block */

$ git grep -w s_reserved lib/ext2fs/ e2fsck/
lib/ext2fs/ext2_fs.h:777:       __le32  s_reserved[94];         /* Padding to the end of the block */
lib/ext2fs/swapfs.c:135:        /* catch when new fields are used from s_reserved */
lib/ext2fs/swapfs.c:136:        EXT2FS_BUILD_BUG_ON(sizeof(sb->s_reserved) != 94 * sizeof(__le32));
lib/ext2fs/tst_super_size.c:156:        check_field(s_reserved, 94 * 4);

Is there a risk that some garbage written to s_reserved (and not caught
by either the kernel or e2fsck) will now appear as a "legitimate" resuid
value?

--D

>  	__le32	s_checksum;		/* crc32c(superblock) */
>  };
>  
> @@ -1812,6 +1814,18 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
>  		 ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
>  }
>  
> +static inline int ext4_get_resuid(struct ext4_super_block *es)
> +{
> +	return(le16_to_cpu(es->s_def_resuid) |
> +	       (le16_to_cpu(es->s_def_resuid_hi) << 16));
> +}
> +
> +static inline int ext4_get_resgid(struct ext4_super_block *es)
> +{
> +	return(le16_to_cpu(es->s_def_resgid) |
> +	       (le16_to_cpu(es->s_def_resgid_hi) << 16));
> +}
> +
>  /*
>   * Returns: sbi->field[index]
>   * Used to access an array element from the following sbi fields which require
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 94c98446c84f9a4614971d246ca7f001de610a8a..0256c8f7c6cee2b8d9295f2fa9a7acd904382e83 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2951,11 +2951,11 @@ static int _ext4_show_options(struct seq_file *seq, struct super_block *sb,
>  	}
>  
>  	if (nodefs || !uid_eq(sbi->s_resuid, make_kuid(&init_user_ns, EXT4_DEF_RESUID)) ||
> -	    le16_to_cpu(es->s_def_resuid) != EXT4_DEF_RESUID)
> +	    ext4_get_resuid(es) != EXT4_DEF_RESUID)
>  		SEQ_OPTS_PRINT("resuid=%u",
>  				from_kuid_munged(&init_user_ns, sbi->s_resuid));
>  	if (nodefs || !gid_eq(sbi->s_resgid, make_kgid(&init_user_ns, EXT4_DEF_RESGID)) ||
> -	    le16_to_cpu(es->s_def_resgid) != EXT4_DEF_RESGID)
> +	    ext4_get_resgid(es) != EXT4_DEF_RESGID)
>  		SEQ_OPTS_PRINT("resgid=%u",
>  				from_kgid_munged(&init_user_ns, sbi->s_resgid));
>  	def_errors = nodefs ? -1 : le16_to_cpu(es->s_errors);
> @@ -5270,8 +5270,8 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
>  
>  	ext4_set_def_opts(sb, es);
>  
> -	sbi->s_resuid = make_kuid(&init_user_ns, le16_to_cpu(es->s_def_resuid));
> -	sbi->s_resgid = make_kgid(&init_user_ns, le16_to_cpu(es->s_def_resgid));
> +	sbi->s_resuid = make_kuid(&init_user_ns, ext4_get_resuid(es));
> +	sbi->s_resgid = make_kgid(&init_user_ns, ext4_get_resuid(es));
>  	sbi->s_commit_interval = JBD2_DEFAULT_MAX_COMMIT_AGE * HZ;
>  	sbi->s_min_batch_time = EXT4_DEF_MIN_BATCH_TIME;
>  	sbi->s_max_batch_time = EXT4_DEF_MAX_BATCH_TIME;
> 
> -- 
> 2.51.0
> 
> 
> 

Re: [PATCH 2/3] ext4: add support for 32-bit default reserved uid and gid values

[Theodore Ts'o]

On Thu, Sep 11, 2025 at 03:31:21PM -0700, Darrick J. Wong wrote:
> 
> Is there a risk that some garbage written to s_reserved (and not caught
> by either the kernel or e2fsck) will now appear as a "legitimate" resuid
> value?

The superblock is checksumed, so the risk would be that some
impleentation modifies the superblock and updates s_reserved for some
reason.  But they could do that to any superblock field, or to the low
16 bits of s_resuid/s_resgid today, and that's something that neither
the kernel or e2fsck could check.

The mke2fs program zeroes all of the unused/reserved portions of the
superblock, so the risk is some random non-Linux implementation (e.g.,
GNU Hurd or BSD) had hijacked some reserved field without coordinating
with upstream ext4.  I thought about using some kind of compat feature
flag, but it probably wouldn't help since the other implementation
would likely not bother to use their own feature flag since that would
prevent the file system to be mounted with Linux.

Currently, someone tried to run "tune2fs -u 146878 /tmp/foo.img" we'll
silently drop the high 16 bits:

% tune2fs -u 146878 /tmp/foo.img 
tune2fs 1.47.3-rc2 (12-Jun-2025)
Setting reserved blocks uid to 146878
% dumpe2fs -h /tmp/foo.img | grep uid
dumpe2fs 1.47.3-rc2 (12-Jun-2025)
Reserved blocks uid:      15806 (user tytso)

And if we have implementations that support 32-bit reserved
uid's/gid's, and the file system is mounted on an older kernel, it
will simply use a different reserved uid (e.g., 15806 instead of
146878).  But we're kind of confused today, and in practice most of
the time people will be using low reserved uid's/gid's (e.g., 1 for
daemon, etc.).

						- Ted

[PATCH 3/3] ext4: implemet new ioctls to set and get superblock parameters

[Theodore Ts'o]

Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
parameters to be set while the file system is mounted, without needing
write access to the block device.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/ioctl.c           | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 include/uapi/linux/ext4.h |  75 ++++++++++++++++++++++
 2 files changed, 324 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..569c98c962af63130c0119f60788a26a2807bd86 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -27,14 +27,16 @@
 #include "fsmap.h"
 #include <trace/events/ext4.h>
 
-typedef void ext4_update_sb_callback(struct ext4_super_block *es,
-				       const void *arg);
+typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
+				     struct ext4_super_block *es,
+				     const void *arg);
 
 /*
  * Superblock modification callback function for changing file system
  * label
  */
-static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
+			     struct ext4_super_block *es, const void *arg)
 {
 	/* Sanity check, this should never happen */
 	BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
@@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
  * Superblock modification callback function for changing file system
  * UUID.
  */
-static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
+			    struct ext4_super_block *es, const void *arg)
 {
 	memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
 }
@@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
 		goto out_err;
 
 	lock_buffer(bh);
-	func(es, arg);
+	func(sbi, es, arg);
 	ext4_superblock_csum_set(sb);
 	unlock_buffer(bh);
 
@@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
 		unlock_buffer(bh);
 		goto out_bh;
 	}
-	func(es, arg);
+	func(EXT4_SB(sb), es, arg);
 	if (ext4_has_feature_metadata_csum(sb))
 		es->s_checksum = ext4_superblock_csum(es);
 	set_buffer_uptodate(bh);
@@ -1230,6 +1233,239 @@ static int ext4_ioctl_setuuid(struct file *filp,
 	return ret;
 }
 
+
+#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR |    \
+	EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
+	EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
+	EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
+	EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
+	EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
+	EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
+	EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
+	EXT4_TUNE_FL_FORCE_FSCK)
+
+static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
+				  struct ext4_tune_sb_params __user *params)
+{
+	struct ext4_tune_sb_params ret;
+	struct ext4_super_block *es = sbi->s_es;
+
+	memset(&ret, 0, sizeof(ret));
+	ret.set_flags = TUNE_OPS_SUPPORTED;
+	ret.errors_behavior = es->s_errors;
+	ret.mnt_count = le16_to_cpu(es->s_mnt_count);
+	ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
+	ret.checkinterval = le32_to_cpu(es->s_checkinterval);
+	ret.last_check_time = le32_to_cpu(es->s_lastcheck);
+	ret.reserved_blocks = ext4_r_blocks_count(es);
+	ret.blocks_count = ext4_blocks_count(es);
+	ret.reserved_uid = ext4_get_resuid(es);
+	ret.reserved_gid = ext4_get_resgid(es);
+	ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
+	ret.def_hash_alg = es->s_def_hash_version;
+	ret.raid_stride = le16_to_cpu(es->s_raid_stride);
+	ret.raid_stripe_width = le16_to_cpu(es->s_raid_stripe_width);
+	strscpy_pad(ret.mount_opts, es->s_mount_opts);
+	ret.feature_compat = le32_to_cpu(es->s_feature_compat);
+	ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
+	ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
+	ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
+	ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
+	ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
+	ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
+	ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
+	ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
+	if (copy_to_user(params, &ret, sizeof(ret)))
+		return -EFAULT;
+	return 0;
+}
+
+static void ext4_sb_setparams(struct ext4_sb_info *sbi,
+			      struct ext4_super_block *es, const void *arg)
+{
+	const struct ext4_tune_sb_params *params = arg;
+
+	if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
+		es->s_errors = cpu_to_le16(params->errors_behavior);
+	if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
+		es->s_mnt_count = cpu_to_le16(params->mnt_count);
+	if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
+		es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
+	if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
+		es->s_checkinterval = cpu_to_le32(params->checkinterval);
+	if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
+		es->s_lastcheck = cpu_to_le32(params->last_check_time);
+	if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
+		ext4_fsblk_t blk = params->reserved_blocks;
+
+		es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
+		es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
+		int uid = params->reserved_uid;
+
+		es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
+		es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
+		int gid = params->reserved_gid;
+
+		es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
+		es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
+		es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
+	if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+		es->s_def_hash_version = params->def_hash_alg;
+	if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
+		es->s_raid_stride = cpu_to_le16(params->raid_stride);
+	if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
+		es->s_raid_stripe_width =
+			cpu_to_le16(params->raid_stripe_width);
+	strscpy_pad(es->s_mount_opts, params->mount_opts);
+	if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+		es->s_feature_compat |=
+			cpu_to_le32(params->set_feature_compat_mask);
+		es->s_feature_incompat |=
+			cpu_to_le32(params->set_feature_incompat_mask);
+		es->s_feature_ro_compat |=
+			cpu_to_le32(params->set_feature_ro_compat_mask);
+		es->s_feature_compat &=
+			~cpu_to_le32(params->clear_feature_compat_mask);
+		es->s_feature_incompat &=
+			~cpu_to_le32(params->clear_feature_incompat_mask);
+		es->s_feature_ro_compat &=
+			~cpu_to_le32(params->clear_feature_ro_compat_mask);
+		if (params->set_feature_compat_mask &
+		    EXT4_FEATURE_COMPAT_DIR_INDEX)
+			es->s_def_hash_version = sbi->s_def_hash_version;
+		if (params->set_feature_incompat_mask &
+		    EXT4_FEATURE_INCOMPAT_CSUM_SEED)
+			es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
+		es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
+}
+
+static int ext4_ioctl_set_tune_sb(struct file *filp,
+				  struct ext4_tune_sb_params __user *in)
+{
+	struct ext4_tune_sb_params params;
+	struct super_block *sb = file_inode(filp)->i_sb;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (copy_from_user(&params, in, sizeof(params)))
+		return -EFAULT;
+
+	if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
+		return -EOPNOTSUPP;
+
+	if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
+	    (params.errors_behavior > EXT4_ERRORS_PANIC))
+		return -EINVAL;
+
+	if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
+	    (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
+		return -EINVAL;
+	if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
+	    ((params.def_hash_alg > DX_HASH_LAST) ||
+	     (params.def_hash_alg == DX_HASH_SIPHASH)))
+		return -EINVAL;
+	if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
+	    (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
+		return -EINVAL;
+
+	if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
+		params.set_feature_compat_mask =
+			params.feature_compat &
+			~le32_to_cpu(es->s_feature_compat);
+		params.set_feature_incompat_mask =
+			params.feature_incompat &
+			~le32_to_cpu(es->s_feature_incompat);
+		params.set_feature_ro_compat_mask =
+			params.feature_ro_compat &
+			~le32_to_cpu(es->s_feature_ro_compat);
+		params.clear_feature_compat_mask =
+			~params.feature_compat &
+			le32_to_cpu(es->s_feature_compat);
+		params.clear_feature_incompat_mask =
+			~params.feature_incompat &
+			le32_to_cpu(es->s_feature_incompat);
+		params.clear_feature_ro_compat_mask =
+			~params.feature_ro_compat &
+			le32_to_cpu(es->s_feature_ro_compat);
+		params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
+	}
+	if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+		if ((params.set_feature_compat_mask &
+		     ~EXT4_TUNE_SET_COMPAT_SUPP) ||
+		    (params.set_feature_incompat_mask &
+		     ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
+		    (params.set_feature_ro_compat_mask &
+		     ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
+		    (params.clear_feature_compat_mask &
+		     ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
+		    (params.clear_feature_incompat_mask &
+		     ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
+		    (params.clear_feature_ro_compat_mask &
+		     ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
+			return -EOPNOTSUPP;
+
+		/*
+		 * Filter out the features that are already set from
+		 * the set_mask.
+		 */
+		params.set_feature_compat_mask &=
+			~le32_to_cpu(es->s_feature_compat);
+		params.set_feature_incompat_mask &=
+			~le32_to_cpu(es->s_feature_incompat);
+		params.set_feature_ro_compat_mask &=
+			~le32_to_cpu(es->s_feature_ro_compat);
+		if ((params.set_feature_compat_mask &
+		     EXT4_FEATURE_COMPAT_DIR_INDEX) &&
+		    !ext4_has_feature_dir_index(sb)) {
+			uuid_t	uu;
+
+			memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
+			if (uuid_is_null(&uu))
+				generate_random_uuid((char *)
+						     &sbi->s_hash_seed);
+			if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+				sbi->s_def_hash_version = params.def_hash_alg;
+			else if (sbi->s_def_hash_version == 0)
+				sbi->s_def_hash_version = DX_HASH_HALF_MD4;
+			if (!(es->s_flags &
+			      cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
+			    !(es->s_flags &
+			      cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
+#ifdef __CHAR_UNSIGNED__
+				sbi->s_hash_unsigned = 3;
+#else
+				sbi->s_hash_unsigned = 0;
+#endif
+			}
+		}
+	}
+
+
+	ret = mnt_want_write_file(filp);
+	if (ret)
+		return ret;
+
+	ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, &params);
+	mnt_drop_write_file(filp);
+
+	if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+		sbi->s_def_hash_version = params.def_hash_alg;
+
+	return ret;
+}
+
 static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -1616,6 +1852,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
 	case EXT4_IOC_SETFSUUID:
 		return ext4_ioctl_setuuid(filp, (const void __user *)arg);
+	case EXT4_IOC_GET_TUNE_SB_PARAM:
+		return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
+					      (void __user *)arg);
+	case EXT4_IOC_SET_TUNE_SB_PARAM:
+		return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
 	default:
 		return -ENOTTY;
 	}
@@ -1703,7 +1944,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 }
 #endif
 
-static void set_overhead(struct ext4_super_block *es, const void *arg)
+static void set_overhead(struct ext4_sb_info *sbi,
+			 struct ext4_super_block *es, const void *arg)
 {
 	es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
 }
diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..145875fd633772e76ce7fd8bc0fef136ff620d2d 100644
--- a/include/uapi/linux/ext4.h
+++ b/include/uapi/linux/ext4.h
@@ -33,6 +33,8 @@
 #define EXT4_IOC_CHECKPOINT		_IOW('f', 43, __u32)
 #define EXT4_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
 #define EXT4_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
+#define EXT4_IOC_GET_TUNE_SB_PARAM	_IOR('f', 45, struct ext4_tune_sb_params)
+#define EXT4_IOC_SET_TUNE_SB_PARAM	_IOW('f', 46, struct ext4_tune_sb_params)
 
 #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
 
@@ -108,6 +110,79 @@ struct ext4_new_group_input {
 	__u16 unused;
 };
 
+struct ext4_tune_sb_params {
+	__u32 set_flags;
+	__u32 checkinterval;
+	__u16 errors_behavior;
+	__u16 mnt_count;
+	__u16 max_mnt_count;
+	__u16 raid_stride;
+	__u64 last_check_time;
+	__u64 reserved_blocks;
+	__u64 blocks_count;
+	__u32 default_mnt_opts;
+	__u32 reserved_uid;
+	__u32 reserved_gid;
+	__u32 raid_stripe_width;
+	__u8  def_hash_alg;
+	__u8  pad_1;
+	__u16 pad_2;
+	__u32 feature_compat;
+	__u32 feature_incompat;
+	__u32 feature_ro_compat;
+	__u32 set_feature_compat_mask;
+	__u32 set_feature_incompat_mask;
+	__u32 set_feature_ro_compat_mask;
+	__u32 clear_feature_compat_mask;
+	__u32 clear_feature_incompat_mask;
+	__u32 clear_feature_ro_compat_mask;
+	__u8  mount_opts[64];
+	__u8  pad[64];
+};
+
+#define EXT4_TUNE_FL_ERRORS_BEHAVIOR	0x00000001
+#define EXT4_TUNE_FL_MNT_COUNT		0x00000002
+#define EXT4_TUNE_FL_MAX_MNT_COUNT	0x00000004
+#define EXT4_TUNE_FL_CHECKINTRVAL	0x00000008
+#define EXT4_TUNE_FL_LAST_CHECK_TIME	0x00000010
+#define EXT4_TUNE_FL_RESERVED_BLOCKS	0x00000020
+#define EXT4_TUNE_FL_RESERVED_UID	0x00000040
+#define EXT4_TUNE_FL_RESERVED_GID	0x00000080
+#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS	0x00000100
+#define EXT4_TUNE_FL_DEF_HASH_ALG	0x00000200
+#define EXT4_TUNE_FL_RAID_STRIDE	0x00000400
+#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH	0x00000800
+#define EXT4_TUNE_FL_MOUNT_OPTS		0x00001000
+#define EXT4_TUNE_FL_FEATURES		0x00002000
+#define EXT4_TUNE_FL_EDIT_FEATURES	0x00004000
+#define EXT4_TUNE_FL_FORCE_FSCK		0x00008000
+
+#define EXT4_TUNE_SET_COMPAT_SUPP \
+		(EXT4_FEATURE_COMPAT_DIR_INDEX |	\
+		 EXT4_FEATURE_COMPAT_STABLE_INODES)
+#define EXT4_TUNE_SET_INCOMPAT_SUPP \
+		(EXT4_FEATURE_INCOMPAT_EXTENTS |	\
+		 EXT4_FEATURE_INCOMPAT_EA_INODE |	\
+		 EXT4_FEATURE_INCOMPAT_ENCRYPT |	\
+		 EXT4_FEATURE_INCOMPAT_CSUM_SEED |	\
+		 EXT4_FEATURE_INCOMPAT_LARGEDIR |	\
+		 EXT4_FEATURE_INCOMPAT_CASEFOLD)
+#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
+		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
+		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
+		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
+		 EXT4_FEATURE_RO_COMPAT_READONLY |	\
+		 EXT4_FEATURE_RO_COMPAT_PROJECT |	\
+		 EXT4_FEATURE_RO_COMPAT_VERITY)
+
+#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP \
+		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
+		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
+		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
+		 EXT4_FEATURE_RO_COMPAT_PROJECT)
+
 /*
  * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
  * It indicates that the entry in extent status cache is for a hole.

-- 
2.51.0

[PATCH 3/3] ext4: implemet new ioctls to set and get superblock parameters

[Theodore Ts'o via B4 Relay]

From: Theodore Ts'o <tytso@mit.edu>

Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
parameters to be set while the file system is mounted, without needing
write access to the block device.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
 fs/ext4/ioctl.c           | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 include/uapi/linux/ext4.h |  75 ++++++++++++++++++++++
 2 files changed, 324 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..569c98c962af63130c0119f60788a26a2807bd86 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -27,14 +27,16 @@
 #include "fsmap.h"
 #include <trace/events/ext4.h>
 
-typedef void ext4_update_sb_callback(struct ext4_super_block *es,
-				       const void *arg);
+typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
+				     struct ext4_super_block *es,
+				     const void *arg);
 
 /*
  * Superblock modification callback function for changing file system
  * label
  */
-static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
+			     struct ext4_super_block *es, const void *arg)
 {
 	/* Sanity check, this should never happen */
 	BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
@@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
  * Superblock modification callback function for changing file system
  * UUID.
  */
-static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
+static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
+			    struct ext4_super_block *es, const void *arg)
 {
 	memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
 }
@@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
 		goto out_err;
 
 	lock_buffer(bh);
-	func(es, arg);
+	func(sbi, es, arg);
 	ext4_superblock_csum_set(sb);
 	unlock_buffer(bh);
 
@@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
 		unlock_buffer(bh);
 		goto out_bh;
 	}
-	func(es, arg);
+	func(EXT4_SB(sb), es, arg);
 	if (ext4_has_feature_metadata_csum(sb))
 		es->s_checksum = ext4_superblock_csum(es);
 	set_buffer_uptodate(bh);
@@ -1230,6 +1233,239 @@ static int ext4_ioctl_setuuid(struct file *filp,
 	return ret;
 }
 
+
+#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR |    \
+	EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
+	EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
+	EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
+	EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
+	EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
+	EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
+	EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
+	EXT4_TUNE_FL_FORCE_FSCK)
+
+static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
+				  struct ext4_tune_sb_params __user *params)
+{
+	struct ext4_tune_sb_params ret;
+	struct ext4_super_block *es = sbi->s_es;
+
+	memset(&ret, 0, sizeof(ret));
+	ret.set_flags = TUNE_OPS_SUPPORTED;
+	ret.errors_behavior = es->s_errors;
+	ret.mnt_count = le16_to_cpu(es->s_mnt_count);
+	ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
+	ret.checkinterval = le32_to_cpu(es->s_checkinterval);
+	ret.last_check_time = le32_to_cpu(es->s_lastcheck);
+	ret.reserved_blocks = ext4_r_blocks_count(es);
+	ret.blocks_count = ext4_blocks_count(es);
+	ret.reserved_uid = ext4_get_resuid(es);
+	ret.reserved_gid = ext4_get_resgid(es);
+	ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
+	ret.def_hash_alg = es->s_def_hash_version;
+	ret.raid_stride = le16_to_cpu(es->s_raid_stride);
+	ret.raid_stripe_width = le16_to_cpu(es->s_raid_stripe_width);
+	strscpy_pad(ret.mount_opts, es->s_mount_opts);
+	ret.feature_compat = le32_to_cpu(es->s_feature_compat);
+	ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
+	ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
+	ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
+	ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
+	ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
+	ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
+	ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
+	ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
+	if (copy_to_user(params, &ret, sizeof(ret)))
+		return -EFAULT;
+	return 0;
+}
+
+static void ext4_sb_setparams(struct ext4_sb_info *sbi,
+			      struct ext4_super_block *es, const void *arg)
+{
+	const struct ext4_tune_sb_params *params = arg;
+
+	if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
+		es->s_errors = cpu_to_le16(params->errors_behavior);
+	if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
+		es->s_mnt_count = cpu_to_le16(params->mnt_count);
+	if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
+		es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
+	if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
+		es->s_checkinterval = cpu_to_le32(params->checkinterval);
+	if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
+		es->s_lastcheck = cpu_to_le32(params->last_check_time);
+	if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
+		ext4_fsblk_t blk = params->reserved_blocks;
+
+		es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
+		es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
+		int uid = params->reserved_uid;
+
+		es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
+		es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
+		int gid = params->reserved_gid;
+
+		es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
+		es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
+		es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
+	if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+		es->s_def_hash_version = params->def_hash_alg;
+	if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
+		es->s_raid_stride = cpu_to_le16(params->raid_stride);
+	if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
+		es->s_raid_stripe_width =
+			cpu_to_le16(params->raid_stripe_width);
+	strscpy_pad(es->s_mount_opts, params->mount_opts);
+	if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+		es->s_feature_compat |=
+			cpu_to_le32(params->set_feature_compat_mask);
+		es->s_feature_incompat |=
+			cpu_to_le32(params->set_feature_incompat_mask);
+		es->s_feature_ro_compat |=
+			cpu_to_le32(params->set_feature_ro_compat_mask);
+		es->s_feature_compat &=
+			~cpu_to_le32(params->clear_feature_compat_mask);
+		es->s_feature_incompat &=
+			~cpu_to_le32(params->clear_feature_incompat_mask);
+		es->s_feature_ro_compat &=
+			~cpu_to_le32(params->clear_feature_ro_compat_mask);
+		if (params->set_feature_compat_mask &
+		    EXT4_FEATURE_COMPAT_DIR_INDEX)
+			es->s_def_hash_version = sbi->s_def_hash_version;
+		if (params->set_feature_incompat_mask &
+		    EXT4_FEATURE_INCOMPAT_CSUM_SEED)
+			es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
+	}
+	if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
+		es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
+}
+
+static int ext4_ioctl_set_tune_sb(struct file *filp,
+				  struct ext4_tune_sb_params __user *in)
+{
+	struct ext4_tune_sb_params params;
+	struct super_block *sb = file_inode(filp)->i_sb;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (copy_from_user(&params, in, sizeof(params)))
+		return -EFAULT;
+
+	if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
+		return -EOPNOTSUPP;
+
+	if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
+	    (params.errors_behavior > EXT4_ERRORS_PANIC))
+		return -EINVAL;
+
+	if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
+	    (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
+		return -EINVAL;
+	if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
+	    ((params.def_hash_alg > DX_HASH_LAST) ||
+	     (params.def_hash_alg == DX_HASH_SIPHASH)))
+		return -EINVAL;
+	if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
+	    (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
+		return -EINVAL;
+
+	if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
+		params.set_feature_compat_mask =
+			params.feature_compat &
+			~le32_to_cpu(es->s_feature_compat);
+		params.set_feature_incompat_mask =
+			params.feature_incompat &
+			~le32_to_cpu(es->s_feature_incompat);
+		params.set_feature_ro_compat_mask =
+			params.feature_ro_compat &
+			~le32_to_cpu(es->s_feature_ro_compat);
+		params.clear_feature_compat_mask =
+			~params.feature_compat &
+			le32_to_cpu(es->s_feature_compat);
+		params.clear_feature_incompat_mask =
+			~params.feature_incompat &
+			le32_to_cpu(es->s_feature_incompat);
+		params.clear_feature_ro_compat_mask =
+			~params.feature_ro_compat &
+			le32_to_cpu(es->s_feature_ro_compat);
+		params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
+	}
+	if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
+		if ((params.set_feature_compat_mask &
+		     ~EXT4_TUNE_SET_COMPAT_SUPP) ||
+		    (params.set_feature_incompat_mask &
+		     ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
+		    (params.set_feature_ro_compat_mask &
+		     ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
+		    (params.clear_feature_compat_mask &
+		     ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
+		    (params.clear_feature_incompat_mask &
+		     ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
+		    (params.clear_feature_ro_compat_mask &
+		     ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
+			return -EOPNOTSUPP;
+
+		/*
+		 * Filter out the features that are already set from
+		 * the set_mask.
+		 */
+		params.set_feature_compat_mask &=
+			~le32_to_cpu(es->s_feature_compat);
+		params.set_feature_incompat_mask &=
+			~le32_to_cpu(es->s_feature_incompat);
+		params.set_feature_ro_compat_mask &=
+			~le32_to_cpu(es->s_feature_ro_compat);
+		if ((params.set_feature_compat_mask &
+		     EXT4_FEATURE_COMPAT_DIR_INDEX) &&
+		    !ext4_has_feature_dir_index(sb)) {
+			uuid_t	uu;
+
+			memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
+			if (uuid_is_null(&uu))
+				generate_random_uuid((char *)
+						     &sbi->s_hash_seed);
+			if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+				sbi->s_def_hash_version = params.def_hash_alg;
+			else if (sbi->s_def_hash_version == 0)
+				sbi->s_def_hash_version = DX_HASH_HALF_MD4;
+			if (!(es->s_flags &
+			      cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
+			    !(es->s_flags &
+			      cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
+#ifdef __CHAR_UNSIGNED__
+				sbi->s_hash_unsigned = 3;
+#else
+				sbi->s_hash_unsigned = 0;
+#endif
+			}
+		}
+	}
+
+
+	ret = mnt_want_write_file(filp);
+	if (ret)
+		return ret;
+
+	ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, &params);
+	mnt_drop_write_file(filp);
+
+	if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
+		sbi->s_def_hash_version = params.def_hash_alg;
+
+	return ret;
+}
+
 static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -1616,6 +1852,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
 	case EXT4_IOC_SETFSUUID:
 		return ext4_ioctl_setuuid(filp, (const void __user *)arg);
+	case EXT4_IOC_GET_TUNE_SB_PARAM:
+		return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
+					      (void __user *)arg);
+	case EXT4_IOC_SET_TUNE_SB_PARAM:
+		return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
 	default:
 		return -ENOTTY;
 	}
@@ -1703,7 +1944,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 }
 #endif
 
-static void set_overhead(struct ext4_super_block *es, const void *arg)
+static void set_overhead(struct ext4_sb_info *sbi,
+			 struct ext4_super_block *es, const void *arg)
 {
 	es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
 }
diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..145875fd633772e76ce7fd8bc0fef136ff620d2d 100644
--- a/include/uapi/linux/ext4.h
+++ b/include/uapi/linux/ext4.h
@@ -33,6 +33,8 @@
 #define EXT4_IOC_CHECKPOINT		_IOW('f', 43, __u32)
 #define EXT4_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
 #define EXT4_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
+#define EXT4_IOC_GET_TUNE_SB_PARAM	_IOR('f', 45, struct ext4_tune_sb_params)
+#define EXT4_IOC_SET_TUNE_SB_PARAM	_IOW('f', 46, struct ext4_tune_sb_params)
 
 #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
 
@@ -108,6 +110,79 @@ struct ext4_new_group_input {
 	__u16 unused;
 };
 
+struct ext4_tune_sb_params {
+	__u32 set_flags;
+	__u32 checkinterval;
+	__u16 errors_behavior;
+	__u16 mnt_count;
+	__u16 max_mnt_count;
+	__u16 raid_stride;
+	__u64 last_check_time;
+	__u64 reserved_blocks;
+	__u64 blocks_count;
+	__u32 default_mnt_opts;
+	__u32 reserved_uid;
+	__u32 reserved_gid;
+	__u32 raid_stripe_width;
+	__u8  def_hash_alg;
+	__u8  pad_1;
+	__u16 pad_2;
+	__u32 feature_compat;
+	__u32 feature_incompat;
+	__u32 feature_ro_compat;
+	__u32 set_feature_compat_mask;
+	__u32 set_feature_incompat_mask;
+	__u32 set_feature_ro_compat_mask;
+	__u32 clear_feature_compat_mask;
+	__u32 clear_feature_incompat_mask;
+	__u32 clear_feature_ro_compat_mask;
+	__u8  mount_opts[64];
+	__u8  pad[64];
+};
+
+#define EXT4_TUNE_FL_ERRORS_BEHAVIOR	0x00000001
+#define EXT4_TUNE_FL_MNT_COUNT		0x00000002
+#define EXT4_TUNE_FL_MAX_MNT_COUNT	0x00000004
+#define EXT4_TUNE_FL_CHECKINTRVAL	0x00000008
+#define EXT4_TUNE_FL_LAST_CHECK_TIME	0x00000010
+#define EXT4_TUNE_FL_RESERVED_BLOCKS	0x00000020
+#define EXT4_TUNE_FL_RESERVED_UID	0x00000040
+#define EXT4_TUNE_FL_RESERVED_GID	0x00000080
+#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS	0x00000100
+#define EXT4_TUNE_FL_DEF_HASH_ALG	0x00000200
+#define EXT4_TUNE_FL_RAID_STRIDE	0x00000400
+#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH	0x00000800
+#define EXT4_TUNE_FL_MOUNT_OPTS		0x00001000
+#define EXT4_TUNE_FL_FEATURES		0x00002000
+#define EXT4_TUNE_FL_EDIT_FEATURES	0x00004000
+#define EXT4_TUNE_FL_FORCE_FSCK		0x00008000
+
+#define EXT4_TUNE_SET_COMPAT_SUPP \
+		(EXT4_FEATURE_COMPAT_DIR_INDEX |	\
+		 EXT4_FEATURE_COMPAT_STABLE_INODES)
+#define EXT4_TUNE_SET_INCOMPAT_SUPP \
+		(EXT4_FEATURE_INCOMPAT_EXTENTS |	\
+		 EXT4_FEATURE_INCOMPAT_EA_INODE |	\
+		 EXT4_FEATURE_INCOMPAT_ENCRYPT |	\
+		 EXT4_FEATURE_INCOMPAT_CSUM_SEED |	\
+		 EXT4_FEATURE_INCOMPAT_LARGEDIR |	\
+		 EXT4_FEATURE_INCOMPAT_CASEFOLD)
+#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
+		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
+		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
+		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
+		 EXT4_FEATURE_RO_COMPAT_READONLY |	\
+		 EXT4_FEATURE_RO_COMPAT_PROJECT |	\
+		 EXT4_FEATURE_RO_COMPAT_VERITY)
+
+#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
+#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP \
+		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
+		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
+		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
+		 EXT4_FEATURE_RO_COMPAT_PROJECT)
+
 /*
  * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
  * It indicates that the entry in extent status cache is for a hole.

-- 
2.51.0

Re: [PATCH 3/3] ext4: implemet new ioctls to set and get superblock parameters

[kernel test robot]

Hi Theodore,

kernel test robot noticed the following build warnings:

[auto build test WARNING on b320789d6883cc00ac78ce83bccbfe7ed58afcf0]

url:    https://github.com/intel-lab-lkp/linux/commits/Theodore-Ts-o-via-B4-Relay/ext4-avoid-potential-buffer-over-read-in-parse_apply_sb_mount_options/20250909-111746
base:   b320789d6883cc00ac78ce83bccbfe7ed58afcf0
patch link:    https://lore.kernel.org/r/20250908-tune2fs-v1-3-e3a6929f3355%40mit.edu
patch subject: [PATCH 3/3] ext4: implemet new ioctls to set and get superblock parameters
config: csky-randconfig-r123-20250910 (https://download.01.org/0day-ci/archive/20250910/202509100550.fj5qrPH5-lkp@intel.com/config)
compiler: csky-linux-gcc (GCC) 10.5.0
reproduce: (https://download.01.org/0day-ci/archive/20250910/202509100550.fj5qrPH5-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509100550.fj5qrPH5-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> fs/ext4/ioctl.c:1255:29: sparse: sparse: incorrect type in assignment (different base types) @@     expected unsigned short [addressable] [assigned] [usertype] errors_behavior @@     got restricted __le16 [usertype] s_errors @@
   fs/ext4/ioctl.c:1255:29: sparse:     expected unsigned short [addressable] [assigned] [usertype] errors_behavior
   fs/ext4/ioctl.c:1255:29: sparse:     got restricted __le16 [usertype] s_errors
>> fs/ext4/ioctl.c:1267:33: sparse: sparse: cast to restricted __le16
>> fs/ext4/ioctl.c:1267:33: sparse: sparse: cast from restricted __le32
>> fs/ext4/ioctl.c:1323:41: sparse: sparse: incorrect type in assignment (different base types) @@     expected restricted __le32 [usertype] s_raid_stripe_width @@     got restricted __le16 [usertype] @@
   fs/ext4/ioctl.c:1323:41: sparse:     expected restricted __le32 [usertype] s_raid_stripe_width
   fs/ext4/ioctl.c:1323:41: sparse:     got restricted __le16 [usertype]
   fs/ext4/ioctl.c: note: in included file (through include/linux/uaccess.h, include/linux/sched/task.h, include/linux/sched/signal.h, ...):
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: cast removes address space '__user' of expression
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: asm output is not an lvalue
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: cast removes address space '__user' of expression
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: cast removes address space '__user' of expression
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: asm output is not an lvalue
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: cast removes address space '__user' of expression
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: generating address of non-lvalue (11)
   arch/csky/include/asm/uaccess.h:110:17: sparse: sparse: generating address of non-lvalue (11)

vim +1255 fs/ext4/ioctl.c

  1235	
  1236	
  1237	#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR |    \
  1238		EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
  1239		EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
  1240		EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
  1241		EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
  1242		EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
  1243		EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
  1244		EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
  1245		EXT4_TUNE_FL_FORCE_FSCK)
  1246	
  1247	static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
  1248					  struct ext4_tune_sb_params __user *params)
  1249	{
  1250		struct ext4_tune_sb_params ret;
  1251		struct ext4_super_block *es = sbi->s_es;
  1252	
  1253		memset(&ret, 0, sizeof(ret));
  1254		ret.set_flags = TUNE_OPS_SUPPORTED;
> 1255		ret.errors_behavior = es->s_errors;
  1256		ret.mnt_count = le16_to_cpu(es->s_mnt_count);
  1257		ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
  1258		ret.checkinterval = le32_to_cpu(es->s_checkinterval);
  1259		ret.last_check_time = le32_to_cpu(es->s_lastcheck);
  1260		ret.reserved_blocks = ext4_r_blocks_count(es);
  1261		ret.blocks_count = ext4_blocks_count(es);
  1262		ret.reserved_uid = ext4_get_resuid(es);
  1263		ret.reserved_gid = ext4_get_resgid(es);
  1264		ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
  1265		ret.def_hash_alg = es->s_def_hash_version;
  1266		ret.raid_stride = le16_to_cpu(es->s_raid_stride);
> 1267		ret.raid_stripe_width = le16_to_cpu(es->s_raid_stripe_width);
  1268		strscpy_pad(ret.mount_opts, es->s_mount_opts);
  1269		ret.feature_compat = le32_to_cpu(es->s_feature_compat);
  1270		ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
  1271		ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
  1272		ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
  1273		ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
  1274		ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
  1275		ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
  1276		ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
  1277		ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
  1278		if (copy_to_user(params, &ret, sizeof(ret)))
  1279			return -EFAULT;
  1280		return 0;
  1281	}
  1282	
  1283	static void ext4_sb_setparams(struct ext4_sb_info *sbi,
  1284				      struct ext4_super_block *es, const void *arg)
  1285	{
  1286		const struct ext4_tune_sb_params *params = arg;
  1287	
  1288		if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
  1289			es->s_errors = cpu_to_le16(params->errors_behavior);
  1290		if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
  1291			es->s_mnt_count = cpu_to_le16(params->mnt_count);
  1292		if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
  1293			es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
  1294		if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
  1295			es->s_checkinterval = cpu_to_le32(params->checkinterval);
  1296		if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
  1297			es->s_lastcheck = cpu_to_le32(params->last_check_time);
  1298		if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
  1299			ext4_fsblk_t blk = params->reserved_blocks;
  1300	
  1301			es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
  1302			es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
  1303		}
  1304		if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
  1305			int uid = params->reserved_uid;
  1306	
  1307			es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
  1308			es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
  1309		}
  1310		if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
  1311			int gid = params->reserved_gid;
  1312	
  1313			es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
  1314			es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
  1315		}
  1316		if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
  1317			es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
  1318		if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
  1319			es->s_def_hash_version = params->def_hash_alg;
  1320		if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
  1321			es->s_raid_stride = cpu_to_le16(params->raid_stride);
  1322		if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
> 1323			es->s_raid_stripe_width =
  1324				cpu_to_le16(params->raid_stripe_width);
  1325		strscpy_pad(es->s_mount_opts, params->mount_opts);
  1326		if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
  1327			es->s_feature_compat |=
  1328				cpu_to_le32(params->set_feature_compat_mask);
  1329			es->s_feature_incompat |=
  1330				cpu_to_le32(params->set_feature_incompat_mask);
  1331			es->s_feature_ro_compat |=
  1332				cpu_to_le32(params->set_feature_ro_compat_mask);
  1333			es->s_feature_compat &=
  1334				~cpu_to_le32(params->clear_feature_compat_mask);
  1335			es->s_feature_incompat &=
  1336				~cpu_to_le32(params->clear_feature_incompat_mask);
  1337			es->s_feature_ro_compat &=
  1338				~cpu_to_le32(params->clear_feature_ro_compat_mask);
  1339			if (params->set_feature_compat_mask &
  1340			    EXT4_FEATURE_COMPAT_DIR_INDEX)
  1341				es->s_def_hash_version = sbi->s_def_hash_version;
  1342			if (params->set_feature_incompat_mask &
  1343			    EXT4_FEATURE_INCOMPAT_CSUM_SEED)
  1344				es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
  1345		}
  1346		if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
  1347			es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
  1348	}
  1349	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 3/3] ext4: implemet new ioctls to set and get superblock parameters

[Darrick J. Wong]

On Mon, Sep 08, 2025 at 11:15:50PM -0400, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@mit.edu>
> 
> Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
> EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
> parameters to be set while the file system is mounted, without needing
> write access to the block device.
> 
> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
> ---
>  fs/ext4/ioctl.c           | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  include/uapi/linux/ext4.h |  75 ++++++++++++++++++++++
>  2 files changed, 324 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..569c98c962af63130c0119f60788a26a2807bd86 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -27,14 +27,16 @@
>  #include "fsmap.h"
>  #include <trace/events/ext4.h>
>  
> -typedef void ext4_update_sb_callback(struct ext4_super_block *es,
> -				       const void *arg);
> +typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
> +				     struct ext4_super_block *es,
> +				     const void *arg);
>  
>  /*
>   * Superblock modification callback function for changing file system
>   * label
>   */
> -static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
> +			     struct ext4_super_block *es, const void *arg)
>  {
>  	/* Sanity check, this should never happen */
>  	BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
> @@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
>   * Superblock modification callback function for changing file system
>   * UUID.
>   */
> -static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
> +			    struct ext4_super_block *es, const void *arg)
>  {
>  	memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
>  }
> @@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
>  		goto out_err;
>  
>  	lock_buffer(bh);
> -	func(es, arg);
> +	func(sbi, es, arg);
>  	ext4_superblock_csum_set(sb);
>  	unlock_buffer(bh);
>  
> @@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
>  		unlock_buffer(bh);
>  		goto out_bh;
>  	}
> -	func(es, arg);
> +	func(EXT4_SB(sb), es, arg);
>  	if (ext4_has_feature_metadata_csum(sb))
>  		es->s_checksum = ext4_superblock_csum(es);
>  	set_buffer_uptodate(bh);
> @@ -1230,6 +1233,239 @@ static int ext4_ioctl_setuuid(struct file *filp,
>  	return ret;
>  }
>  
> +
> +#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR |    \
> +	EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
> +	EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
> +	EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
> +	EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
> +	EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
> +	EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
> +	EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
> +	EXT4_TUNE_FL_FORCE_FSCK)
> +
> +static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
> +				  struct ext4_tune_sb_params __user *params)
> +{
> +	struct ext4_tune_sb_params ret;
> +	struct ext4_super_block *es = sbi->s_es;
> +
> +	memset(&ret, 0, sizeof(ret));
> +	ret.set_flags = TUNE_OPS_SUPPORTED;
> +	ret.errors_behavior = es->s_errors;
> +	ret.mnt_count = le16_to_cpu(es->s_mnt_count);
> +	ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
> +	ret.checkinterval = le32_to_cpu(es->s_checkinterval);
> +	ret.last_check_time = le32_to_cpu(es->s_lastcheck);
> +	ret.reserved_blocks = ext4_r_blocks_count(es);
> +	ret.blocks_count = ext4_blocks_count(es);
> +	ret.reserved_uid = ext4_get_resuid(es);
> +	ret.reserved_gid = ext4_get_resgid(es);
> +	ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
> +	ret.def_hash_alg = es->s_def_hash_version;
> +	ret.raid_stride = le16_to_cpu(es->s_raid_stride);
> +	ret.raid_stripe_width = le16_to_cpu(es->s_raid_stripe_width);
> +	strscpy_pad(ret.mount_opts, es->s_mount_opts);
> +	ret.feature_compat = le32_to_cpu(es->s_feature_compat);
> +	ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
> +	ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
> +	ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
> +	ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
> +	ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
> +	ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
> +	ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
> +	ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
> +	if (copy_to_user(params, &ret, sizeof(ret)))
> +		return -EFAULT;
> +	return 0;
> +}
> +
> +static void ext4_sb_setparams(struct ext4_sb_info *sbi,
> +			      struct ext4_super_block *es, const void *arg)
> +{
> +	const struct ext4_tune_sb_params *params = arg;
> +
> +	if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
> +		es->s_errors = cpu_to_le16(params->errors_behavior);
> +	if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
> +		es->s_mnt_count = cpu_to_le16(params->mnt_count);
> +	if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
> +		es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
> +	if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
> +		es->s_checkinterval = cpu_to_le32(params->checkinterval);
> +	if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
> +		es->s_lastcheck = cpu_to_le32(params->last_check_time);
> +	if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
> +		ext4_fsblk_t blk = params->reserved_blocks;
> +
> +		es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
> +		es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
> +	}
> +	if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
> +		int uid = params->reserved_uid;
> +
> +		es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
> +		es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
> +	}
> +	if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
> +		int gid = params->reserved_gid;
> +
> +		es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
> +		es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
> +	}
> +	if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
> +		es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
> +	if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> +		es->s_def_hash_version = params->def_hash_alg;
> +	if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
> +		es->s_raid_stride = cpu_to_le16(params->raid_stride);
> +	if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
> +		es->s_raid_stripe_width =
> +			cpu_to_le16(params->raid_stripe_width);
> +	strscpy_pad(es->s_mount_opts, params->mount_opts);
> +	if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> +		es->s_feature_compat |=
> +			cpu_to_le32(params->set_feature_compat_mask);
> +		es->s_feature_incompat |=
> +			cpu_to_le32(params->set_feature_incompat_mask);
> +		es->s_feature_ro_compat |=
> +			cpu_to_le32(params->set_feature_ro_compat_mask);
> +		es->s_feature_compat &=
> +			~cpu_to_le32(params->clear_feature_compat_mask);
> +		es->s_feature_incompat &=
> +			~cpu_to_le32(params->clear_feature_incompat_mask);
> +		es->s_feature_ro_compat &=
> +			~cpu_to_le32(params->clear_feature_ro_compat_mask);
> +		if (params->set_feature_compat_mask &
> +		    EXT4_FEATURE_COMPAT_DIR_INDEX)
> +			es->s_def_hash_version = sbi->s_def_hash_version;
> +		if (params->set_feature_incompat_mask &
> +		    EXT4_FEATURE_INCOMPAT_CSUM_SEED)
> +			es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
> +	}
> +	if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
> +		es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
> +}
> +
> +static int ext4_ioctl_set_tune_sb(struct file *filp,
> +				  struct ext4_tune_sb_params __user *in)
> +{
> +	struct ext4_tune_sb_params params;
> +	struct super_block *sb = file_inode(filp)->i_sb;
> +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> +	struct ext4_super_block *es = sbi->s_es;
> +	int ret;
> +
> +	if (!capable(CAP_SYS_ADMIN))
> +		return -EPERM;
> +
> +	if (copy_from_user(&params, in, sizeof(params)))
> +		return -EFAULT;
> +
> +	if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
> +		return -EOPNOTSUPP;
> +
> +	if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
> +	    (params.errors_behavior > EXT4_ERRORS_PANIC))
> +		return -EINVAL;
> +
> +	if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
> +	    (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
> +		return -EINVAL;
> +	if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
> +	    ((params.def_hash_alg > DX_HASH_LAST) ||
> +	     (params.def_hash_alg == DX_HASH_SIPHASH)))
> +		return -EINVAL;
> +	if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
> +	    (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
> +		return -EINVAL;

What's the difference between _FL_FEATURES and _FL_EDIT_FEATURES?

> +
> +	if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
> +		params.set_feature_compat_mask =
> +			params.feature_compat &
> +			~le32_to_cpu(es->s_feature_compat);
> +		params.set_feature_incompat_mask =
> +			params.feature_incompat &
> +			~le32_to_cpu(es->s_feature_incompat);
> +		params.set_feature_ro_compat_mask =
> +			params.feature_ro_compat &
> +			~le32_to_cpu(es->s_feature_ro_compat);
> +		params.clear_feature_compat_mask =
> +			~params.feature_compat &
> +			le32_to_cpu(es->s_feature_compat);
> +		params.clear_feature_incompat_mask =
> +			~params.feature_incompat &
> +			le32_to_cpu(es->s_feature_incompat);
> +		params.clear_feature_ro_compat_mask =
> +			~params.feature_ro_compat &
> +			le32_to_cpu(es->s_feature_ro_compat);
> +		params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
> +	}
> +	if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> +		if ((params.set_feature_compat_mask &
> +		     ~EXT4_TUNE_SET_COMPAT_SUPP) ||
> +		    (params.set_feature_incompat_mask &
> +		     ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
> +		    (params.set_feature_ro_compat_mask &
> +		     ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
> +		    (params.clear_feature_compat_mask &
> +		     ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
> +		    (params.clear_feature_incompat_mask &
> +		     ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
> +		    (params.clear_feature_ro_compat_mask &
> +		     ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
> +			return -EOPNOTSUPP;
> +
> +		/*
> +		 * Filter out the features that are already set from
> +		 * the set_mask.
> +		 */
> +		params.set_feature_compat_mask &=
> +			~le32_to_cpu(es->s_feature_compat);
> +		params.set_feature_incompat_mask &=
> +			~le32_to_cpu(es->s_feature_incompat);
> +		params.set_feature_ro_compat_mask &=
> +			~le32_to_cpu(es->s_feature_ro_compat);
> +		if ((params.set_feature_compat_mask &
> +		     EXT4_FEATURE_COMPAT_DIR_INDEX) &&
> +		    !ext4_has_feature_dir_index(sb)) {
> +			uuid_t	uu;
> +
> +			memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
> +			if (uuid_is_null(&uu))
> +				generate_random_uuid((char *)
> +						     &sbi->s_hash_seed);
> +			if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> +				sbi->s_def_hash_version = params.def_hash_alg;
> +			else if (sbi->s_def_hash_version == 0)
> +				sbi->s_def_hash_version = DX_HASH_HALF_MD4;
> +			if (!(es->s_flags &
> +			      cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
> +			    !(es->s_flags &
> +			      cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
> +#ifdef __CHAR_UNSIGNED__
> +				sbi->s_hash_unsigned = 3;
> +#else
> +				sbi->s_hash_unsigned = 0;
> +#endif
> +			}
> +		}
> +	}
> +
> +
> +	ret = mnt_want_write_file(filp);
> +	if (ret)
> +		return ret;
> +
> +	ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, &params);
> +	mnt_drop_write_file(filp);
> +
> +	if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> +		sbi->s_def_hash_version = params.def_hash_alg;
> +
> +	return ret;
> +}
> +
>  static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  {
>  	struct inode *inode = file_inode(filp);
> @@ -1616,6 +1852,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>  		return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
>  	case EXT4_IOC_SETFSUUID:
>  		return ext4_ioctl_setuuid(filp, (const void __user *)arg);
> +	case EXT4_IOC_GET_TUNE_SB_PARAM:
> +		return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
> +					      (void __user *)arg);
> +	case EXT4_IOC_SET_TUNE_SB_PARAM:
> +		return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
>  	default:
>  		return -ENOTTY;
>  	}
> @@ -1703,7 +1944,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>  }
>  #endif
>  
> -static void set_overhead(struct ext4_super_block *es, const void *arg)
> +static void set_overhead(struct ext4_sb_info *sbi,
> +			 struct ext4_super_block *es, const void *arg)
>  {
>  	es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
>  }
> diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
> index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..145875fd633772e76ce7fd8bc0fef136ff620d2d 100644
> --- a/include/uapi/linux/ext4.h
> +++ b/include/uapi/linux/ext4.h
> @@ -33,6 +33,8 @@
>  #define EXT4_IOC_CHECKPOINT		_IOW('f', 43, __u32)
>  #define EXT4_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
>  #define EXT4_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GET_TUNE_SB_PARAM	_IOR('f', 45, struct ext4_tune_sb_params)
> +#define EXT4_IOC_SET_TUNE_SB_PARAM	_IOW('f', 46, struct ext4_tune_sb_params)
>  
>  #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
>  
> @@ -108,6 +110,79 @@ struct ext4_new_group_input {
>  	__u16 unused;
>  };
>  
> +struct ext4_tune_sb_params {
> +	__u32 set_flags;
> +	__u32 checkinterval;
> +	__u16 errors_behavior;
> +	__u16 mnt_count;
> +	__u16 max_mnt_count;
> +	__u16 raid_stride;
> +	__u64 last_check_time;
> +	__u64 reserved_blocks;
> +	__u64 blocks_count;
> +	__u32 default_mnt_opts;
> +	__u32 reserved_uid;
> +	__u32 reserved_gid;
> +	__u32 raid_stripe_width;
> +	__u8  def_hash_alg;
> +	__u8  pad_1;
> +	__u16 pad_2;
> +	__u32 feature_compat;
> +	__u32 feature_incompat;
> +	__u32 feature_ro_compat;
> +	__u32 set_feature_compat_mask;
> +	__u32 set_feature_incompat_mask;
> +	__u32 set_feature_ro_compat_mask;
> +	__u32 clear_feature_compat_mask;
> +	__u32 clear_feature_incompat_mask;
> +	__u32 clear_feature_ro_compat_mask;
> +	__u8  mount_opts[64];
> +	__u8  pad[64];
> +};
> +
> +#define EXT4_TUNE_FL_ERRORS_BEHAVIOR	0x00000001
> +#define EXT4_TUNE_FL_MNT_COUNT		0x00000002
> +#define EXT4_TUNE_FL_MAX_MNT_COUNT	0x00000004
> +#define EXT4_TUNE_FL_CHECKINTRVAL	0x00000008
> +#define EXT4_TUNE_FL_LAST_CHECK_TIME	0x00000010
> +#define EXT4_TUNE_FL_RESERVED_BLOCKS	0x00000020
> +#define EXT4_TUNE_FL_RESERVED_UID	0x00000040
> +#define EXT4_TUNE_FL_RESERVED_GID	0x00000080
> +#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS	0x00000100
> +#define EXT4_TUNE_FL_DEF_HASH_ALG	0x00000200
> +#define EXT4_TUNE_FL_RAID_STRIDE	0x00000400
> +#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH	0x00000800
> +#define EXT4_TUNE_FL_MOUNT_OPTS		0x00001000
> +#define EXT4_TUNE_FL_FEATURES		0x00002000
> +#define EXT4_TUNE_FL_EDIT_FEATURES	0x00004000
> +#define EXT4_TUNE_FL_FORCE_FSCK		0x00008000
> +
> +#define EXT4_TUNE_SET_COMPAT_SUPP \
> +		(EXT4_FEATURE_COMPAT_DIR_INDEX |	\
> +		 EXT4_FEATURE_COMPAT_STABLE_INODES)
> +#define EXT4_TUNE_SET_INCOMPAT_SUPP \
> +		(EXT4_FEATURE_INCOMPAT_EXTENTS |	\
> +		 EXT4_FEATURE_INCOMPAT_EA_INODE |	\
> +		 EXT4_FEATURE_INCOMPAT_ENCRYPT |	\
> +		 EXT4_FEATURE_INCOMPAT_CSUM_SEED |	\
> +		 EXT4_FEATURE_INCOMPAT_LARGEDIR |	\
> +		 EXT4_FEATURE_INCOMPAT_CASEFOLD)
> +#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
> +		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
> +		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
> +		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
> +		 EXT4_FEATURE_RO_COMPAT_READONLY |	\
> +		 EXT4_FEATURE_RO_COMPAT_PROJECT |	\
> +		 EXT4_FEATURE_RO_COMPAT_VERITY)
> +
> +#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP \
> +		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
> +		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
> +		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
> +		 EXT4_FEATURE_RO_COMPAT_PROJECT)

Is it actually safe to clear these without scanning the filesystem to
make sure nobody's using these features?

--D

> +
>  /*
>   * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
>   * It indicates that the entry in extent status cache is for a hole.
> 
> -- 
> 2.51.0
> 
> 
> 

Re: [PATCH 3/3] ext4: implemet new ioctls to set and get superblock parameters

[Theodore Ts'o]

On Thu, Sep 11, 2025 at 03:40:19PM -0700, Darrick J. Wong wrote:
>
> What's the difference between _FL_FEATURES and _FL_EDIT_FEATURES?

We have three sets of 

_FL_FEATURES allows the user to set the features via:

	__u32 feature_compat;
	__u32 feature_incompat;
	__u32 feature_ro_compat;

... while _FS_EDIT_FEATURES allows the user to set or clear specific
feature or feature(s) using these fields:

	__u32 set_feature_compat_mask;
	__u32 set_feature_incompat_mask;
	__u32 set_feature_ro_compat_mask;
	__u32 clear_feature_compat_mask;
	__u32 clear_feature_incompat_mask;
	__u32 clear_feature_ro_compat_mask;

I originally only implemented _FS_EDIT_EFATURES but it turns out that
given how tune2fs() and e2p_edit_feateurs2() was implemented,
_FS_FEATURES was a lot more convenient.  But I kept _FS_EDIT_FEATURES
in case some other users wanted an easy way to, say, "just enable
feature X" using a single ioctl.

> > +#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
> > +#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
> > +#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP \
> > +		(EXT4_FEATURE_RO_COMPAT_LARGE_FILE |	\
> > +		 EXT4_FEATURE_RO_COMPAT_DIR_NLINK |	\
> > +		 EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE |	\
> > +		 EXT4_FEATURE_RO_COMPAT_PROJECT)
> 
> Is it actually safe to clear these without scanning the filesystem to
> make sure nobody's using these features?

Hmm.... probably not.  For some of these features, tune2fs will issue
a "pleas run e2fsck -f" before mounting the file system.  All of these
featrues tune2fs will allow being cleared on a mounted file system,
but looking at this more closely, I probably *shouldn't* have allowed
tune2fs to remove the feature wile the file system is mounted.  (For
example, tune2fs -O ^project" will try to clear they project quota
inode even if the file system is mounted, hilarity would soon
follow...)

						- Ted