Re: [PATCH 2/2] ntfs3: remove warning

Christian Brauner
2024-04-16T10:39:03Z

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On Mon, Apr 15, 2024 at 06:06:03PM +0200, Johan Hovold wrote:
> On Mon, Apr 15, 2024 at 08:51:13AM -0700, Linus Torvalds wrote:
> > On Mon, 15 Apr 2024 at 08:47, Johan Hovold <johan@kernel.org> wrote:
> > >
> > > I think the "ntfs" alias must always be mounted read-only because you
> > > can currently have an fstab entry which does not specify "ro" and this
> > > mount would suddenly become writeable when updating to 6.9 (possibly by
> > > a non-privileged user, etc).
> >
> > Well, it would be fairly easy to do particularly if we just do it for
> > the old legacy case.
> >
> > Of course, even the legacy case had that CONFIG_NTFS_RW option, so
> > people who depended on _that_ would want to be able to remount...
>
> Ah, right, I forgot about CONFIG_NTFS_RW as I've never enabled it.
>
> Judging from the now removed Kconfig entry perhaps not that many people
> did:
>
> The only supported operation is overwriting existing files,
> without changing the file length. No file or directory
> creation, deletion or renaming is possible.
>
> but I guess it still makes my argument above mostly moot.
>
> At least if we disable write support in ntfs3 by default for now...

I think we can disable write support in ntfs3 for now. I've picked up
the patch to make ntfs3 serve I sent some time ago that Johan tested
now.

The only thing left is to disable write support for ntfs3 as legacy ntfs
driver for now. I took a stab at this. The following two patches
I'm appending _should_ be enough iiuc. Johan, please take a look and
please test.

This is also available on:

https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git vfs.fixes

So feel free to pull from there and look there as well.

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From 1a2af5ca9b66bd3d4040f9987c78faff128e552f Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Tue, 16 Apr 2024 12:08:51 +0200
Subject: [PATCH 1/2] ntfs3: enforce read-only when used as legacy ntfs driver

Ensure that ntfs3 is mounted read-only when it is used to provide the
legacy ntfs driver.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/ntfs3/ntfs_fs.h | 2 ++
fs/ntfs3/super.c | 34 ++++++++++++++++++++++++++++++----
2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/fs/ntfs3/ntfs_fs.h b/fs/ntfs3/ntfs_fs.h
index 79356fd29a14..184c8bc76b92 100644
--- a/fs/ntfs3/ntfs_fs.h
+++ b/fs/ntfs3/ntfs_fs.h
@@ -1154,4 +1154,6 @@ static inline void le64_sub_cpu(__le64 *var, u64 val)
*var = cpu_to_le64(le64_to_cpu(*var) - val);
}

+bool is_legacy_ntfs(struct super_block *sb);
+
#endif /* _LINUX_NTFS3_NTFS_FS_H */
diff --git a/fs/ntfs3/super.c b/fs/ntfs3/super.c
index 8d2e51bae2cb..d7f3e03a4010 100644
--- a/fs/ntfs3/super.c
+++ b/fs/ntfs3/super.c
@@ -408,6 +408,12 @@ static int ntfs_fs_reconfigure(struct fs_context *fc)
struct ntfs_mount_options *new_opts = fc->fs_private;
int ro_rw;

+ /* If ntfs3 is used as legacy ntfs enforce read-only mode. */
+ if (is_legacy_ntfs(sb)) {
+ fc->sb_flags |= SB_RDONLY;
+ goto out;
+ }
+
ro_rw = sb_rdonly(sb) && !(fc->sb_flags & SB_RDONLY);
if (ro_rw && (sbi->flags & NTFS_FLAGS_NEED_REPLAY)) {
errorf(fc,
@@ -427,8 +433,6 @@ static int ntfs_fs_reconfigure(struct fs_context *fc)
fc,
"ntfs3: Cannot use different iocharset when remounting!");

- sync_filesystem(sb);
-
if (ro_rw && (sbi->volume.flags & VOLUME_FLAG_DIRTY) &&
!new_opts->force) {
errorf(fc,
@@ -436,6 +440,8 @@ static int ntfs_fs_reconfigure(struct fs_context *fc)
return -EINVAL;
}

+out:
+ sync_filesystem(sb);
swap(sbi->options, fc->fs_private);

return 0;
@@ -1730,7 +1736,7 @@ static const struct fs_context_operations ntfs_context_ops = {
* This will called when mount/remount. We will first initialize
* options so that if remount we can use just that.
*/
-static int ntfs_init_fs_context(struct fs_context *fc)
+static int __ntfs_init_fs_context(struct fs_context *fc)
{
struct ntfs_mount_options *opts;
struct ntfs_sb_info *sbi;
@@ -1778,6 +1784,11 @@ static int ntfs_init_fs_context(struct fs_context *fc)
return -ENOMEM;
}

+static int ntfs_init_fs_context(struct fs_context *fc)
+{
+ return __ntfs_init_fs_context(fc);
+}
+
static void ntfs3_kill_sb(struct super_block *sb)
{
struct ntfs_sb_info *sbi = sb->s_fs_info;
@@ -1800,10 +1811,20 @@ static struct file_system_type ntfs_fs_type = {
};

#if IS_ENABLED(CONFIG_NTFS_FS)
+static int ntfs_legacy_init_fs_context(struct fs_context *fc)
+{
+ int ret;
+
+ ret = __ntfs_init_fs_context(fc);
+ /* If ntfs3 is used as legacy ntfs enforce read-only mode. */
+ fc->sb_flags |= SB_RDONLY;
+ return ret;
+}
+
static struct file_system_type ntfs_legacy_fs_type = {
.owner = THIS_MODULE,
.name = "ntfs",
- .init_fs_context = ntfs_init_fs_context,
+ .init_fs_context = ntfs_legacy_init_fs_context,
.parameters = ntfs_fs_parameters,
.kill_sb = ntfs3_kill_sb,
.fs_flags = FS_REQUIRES_DEV | FS_ALLOW_IDMAP,
@@ -1821,9 +1842,14 @@ static inline void unregister_as_ntfs_legacy(void)
{
unregister_filesystem(&ntfs_legacy_fs_type);
}
+bool is_legacy_ntfs(struct super_block *sb)
+{
+ return sb->s_type == &ntfs_legacy_fs_type;
+}
#else
static inline void register_as_ntfs_legacy(void) {}
static inline void unregister_as_ntfs_legacy(void) {}
+bool is_legacy_ntfs(struct super_block *sb) { return false; }
#endif

--
2.43.0

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From 5e646f22f0e9d5268d902dfd33a39154c0b5f578 Mon Sep 17 00:00:00 2001
From: Christian Brauner <brauner@kernel.org>
Date: Tue, 16 Apr 2024 12:20:50 +0200
Subject: [PATCH 2/2] ntfs3: add legacy ntfs file operations

To ensure that ioctl()s can't be used to circumvent write restrictions.

Signed-off-by: Christian Brauner <brauner@kernel.org>
---
fs/ntfs3/dir.c | 7 +++++++
fs/ntfs3/file.c | 8 ++++++++
fs/ntfs3/inode.c | 20 ++++++++++++++++----
fs/ntfs3/ntfs_fs.h | 2 ++
4 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/fs/ntfs3/dir.c b/fs/ntfs3/dir.c
index 5cf3d9decf64..263635199b60 100644
--- a/fs/ntfs3/dir.c
+++ b/fs/ntfs3/dir.c
@@ -616,4 +616,11 @@ const struct file_operations ntfs_dir_operations = {
.compat_ioctl = ntfs_compat_ioctl,
#endif
};
+
+const struct file_operations ntfs_legacy_dir_operations = {
+ .llseek = generic_file_llseek,
+ .read = generic_read_dir,
+ .iterate_shared = ntfs_readdir,
+ .open = ntfs_file_open,
+};
// clang-format on
diff --git a/fs/ntfs3/file.c b/fs/ntfs3/file.c
index 5418662c80d8..b73969e05052 100644
--- a/fs/ntfs3/file.c
+++ b/fs/ntfs3/file.c
@@ -1236,4 +1236,12 @@ const struct file_operations ntfs_file_operations = {
.fallocate = ntfs_fallocate,
.release = ntfs_file_release,
};
+
+const struct file_operations ntfs_legacy_file_operations = {
+ .llseek = generic_file_llseek,
+ .read_iter = ntfs_file_read_iter,
+ .splice_read = ntfs_file_splice_read,
+ .open = ntfs_file_open,
+ .release = ntfs_file_release,
+};
// clang-format on
diff --git a/fs/ntfs3/inode.c b/fs/ntfs3/inode.c
index eb7a8c9fba01..d273eda1cf45 100644
--- a/fs/ntfs3/inode.c
+++ b/fs/ntfs3/inode.c
@@ -440,7 +440,10 @@ static struct inode *ntfs_read_mft(struct inode *inode,
* Usually a hard links to directories are disabled.
*/
inode->i_op = &ntfs_dir_inode_operations;
- inode->i_fop = &ntfs_dir_operations;
+ if (is_legacy_ntfs(inode->i_sb))
+ inode->i_fop = &ntfs_legacy_dir_operations;
+ else
+ inode->i_fop = &ntfs_dir_operations;
ni->i_valid = 0;
} else if (S_ISLNK(mode)) {
ni->std_fa &= ~FILE_ATTRIBUTE_DIRECTORY;
@@ -450,7 +453,10 @@ static struct inode *ntfs_read_mft(struct inode *inode,
} else if (S_ISREG(mode)) {
ni->std_fa &= ~FILE_ATTRIBUTE_DIRECTORY;
inode->i_op = &ntfs_file_inode_operations;
- inode->i_fop = &ntfs_file_operations;
+ if (is_legacy_ntfs(inode->i_sb))
+ inode->i_fop = &ntfs_legacy_file_operations;
+ else
+ inode->i_fop = &ntfs_file_operations;
inode->i_mapping->a_ops = is_compressed(ni) ? &ntfs_aops_cmpr :
&ntfs_aops;
if (ino != MFT_REC_MFT)
@@ -1614,7 +1620,10 @@ struct inode *ntfs_create_inode(struct mnt_idmap *idmap, struct inode *dir,

if (S_ISDIR(mode)) {
inode->i_op = &ntfs_dir_inode_operations;
- inode->i_fop = &ntfs_dir_operations;
+ if (is_legacy_ntfs(inode->i_sb))
+ inode->i_fop = &ntfs_legacy_dir_operations;
+ else
+ inode->i_fop = &ntfs_dir_operations;
} else if (S_ISLNK(mode)) {
inode->i_op = &ntfs_link_inode_operations;
inode->i_fop = NULL;
@@ -1623,7 +1632,10 @@ struct inode *ntfs_create_inode(struct mnt_idmap *idmap, struct inode *dir,
inode_nohighmem(inode);
} else if (S_ISREG(mode)) {
inode->i_op = &ntfs_file_inode_operations;
- inode->i_fop = &ntfs_file_operations;
+ if (is_legacy_ntfs(inode->i_sb))
+ inode->i_fop = &ntfs_legacy_file_operations;
+ else
+ inode->i_fop = &ntfs_file_operations;
inode->i_mapping->a_ops = is_compressed(ni) ? &ntfs_aops_cmpr :
&ntfs_aops;
init_rwsem(&ni->file.run_lock);
diff --git a/fs/ntfs3/ntfs_fs.h b/fs/ntfs3/ntfs_fs.h
index 184c8bc76b92..5f4d288c6adf 100644
--- a/fs/ntfs3/ntfs_fs.h
+++ b/fs/ntfs3/ntfs_fs.h
@@ -493,6 +493,7 @@ struct inode *dir_search_u(struct inode *dir, const struct cpu_str *uni,
struct ntfs_fnd *fnd);
bool dir_is_empty(struct inode *dir);
extern const struct file_operations ntfs_dir_operations;
+extern const struct file_operations ntfs_legacy_dir_operations;

/* Globals from file.c */
int ntfs_getattr(struct mnt_idmap *idmap, const struct path *path,
@@ -507,6 +508,7 @@ long ntfs_compat_ioctl(struct file *filp, u32 cmd, unsigned long arg);
extern const struct inode_operations ntfs_special_inode_operations;
extern const struct inode_operations ntfs_file_inode_operations;
extern const struct file_operations ntfs_file_operations;
+extern const struct file_operations ntfs_legacy_file_operations;

/* Globals from frecord.c */
void ni_remove_mi(struct ntfs_inode *ni, struct mft_inode *mi);
--
2.43.0