[PATCH v2] fs: add a new SB_NOUMASK flag

[Jeff Layton <jlayton@kernel.org>]

SB_POSIXACL must be set when a filesystem supports POSIX ACLs, but NFSv4
also sets this flag to prevent the VFS from applying the umask on
newly-created files. NFSv4 doesn't support POSIX ACLs however, which
causes confusion when other subsystems try to test for them.

Split the umask-stripping opt-out into a separate SB_NOUMASK flag, and
have NFSv4 set that instead of SB_POSIXACL. Fix the appropriate places
in the VFS to check for that flag (in addition to SB_POSIXACL) when
stripping the umask.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
Yet another approach to fixing this issue. I think this way is probably
the best, since makes the purpose of these flags clearer, and stops NFS
from relying on SB_POSIXACL to avoid umask stripping.
---
Changes in v2:
- new approach: add a new SB_NOUMASK flag that NFSv4 can use instead of
  SB_POSIXACL
- Link to v1: https://lore.kernel.org/r/20230908-acl-fix-v1-1-1e6b76c8dcc8@kernel.org
---
 fs/init.c          | 4 ++--
 fs/namei.c         | 2 +-
 fs/nfs/super.c     | 2 +-
 include/linux/fs.h | 4 +++-
 4 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/init.c b/fs/init.c
index 9684406a8416..157404bb7d19 100644
--- a/fs/init.c
+++ b/fs/init.c
@@ -153,7 +153,7 @@ int __init init_mknod(const char *filename, umode_t mode, unsigned int dev)
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 
-	if (!IS_POSIXACL(path.dentry->d_inode))
+	if (!IS_NOUMASK(path.dentry->d_inode))
 		mode &= ~current_umask();
 	error = security_path_mknod(&path, dentry, mode, dev);
 	if (!error)
@@ -229,7 +229,7 @@ int __init init_mkdir(const char *pathname, umode_t mode)
 	dentry = kern_path_create(AT_FDCWD, pathname, &path, LOOKUP_DIRECTORY);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
-	if (!IS_POSIXACL(path.dentry->d_inode))
+	if (!IS_NOUMASK(path.dentry->d_inode))
 		mode &= ~current_umask();
 	error = security_path_mkdir(&path, dentry, mode);
 	if (!error)
diff --git a/fs/namei.c b/fs/namei.c
index 567ee547492b..905fdfec5d26 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3117,7 +3117,7 @@ EXPORT_SYMBOL(unlock_rename);
  */
 static inline umode_t mode_strip_umask(const struct inode *dir, umode_t mode)
 {
-	if (!IS_POSIXACL(dir))
+	if (!IS_NOUMASK(dir))
 		mode &= ~current_umask();
 	return mode;
 }
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 0d6473cb00cb..81cd11c4db3d 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -1071,7 +1071,7 @@ static void nfs_fill_super(struct super_block *sb, struct nfs_fs_context *ctx)
 		sb->s_export_op = &nfs_export_ops;
 		break;
 	case 4:
-		sb->s_flags |= SB_POSIXACL;
+		sb->s_flags |= SB_NOUMASK;
 		sb->s_time_gran = 1;
 		sb->s_time_min = S64_MIN;
 		sb->s_time_max = S64_MAX;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4aeb3fa11927..51ad013ca716 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1119,13 +1119,14 @@ extern int send_sigurg(struct fown_struct *fown);
 #define SB_NOATIME      BIT(10)	/* Do not update access times. */
 #define SB_NODIRATIME   BIT(11)	/* Do not update directory access times */
 #define SB_SILENT       BIT(15)
-#define SB_POSIXACL     BIT(16)	/* VFS does not apply the umask */
+#define SB_POSIXACL     BIT(16)	/* POSIX ACLs are supported (implies NOUMASK) */
 #define SB_INLINECRYPT  BIT(17)	/* Use blk-crypto for encrypted files */
 #define SB_KERNMOUNT    BIT(22)	/* this is a kern_mount call */
 #define SB_I_VERSION    BIT(23)	/* Update inode I_version field */
 #define SB_LAZYTIME     BIT(25)	/* Update the on-disk [acm]times lazily */
 
 /* These sb flags are internal to the kernel */
+#define SB_NOUMASK	BIT(20)	/* VFS does not apply the umask */
 #define SB_DEAD         BIT(21)
 #define SB_DYING        BIT(24)
 #define SB_SUBMOUNT     BIT(26)
@@ -2111,6 +2112,7 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
 #define IS_APPEND(inode)	((inode)->i_flags & S_APPEND)
 #define IS_IMMUTABLE(inode)	((inode)->i_flags & S_IMMUTABLE)
 #define IS_POSIXACL(inode)	__IS_FLG(inode, SB_POSIXACL)
+#define IS_NOUMASK(inode)	__IS_FLG(inode, SB_POSIXACL|SB_NOUMASK)
 
 #define IS_DEADDIR(inode)	((inode)->i_flags & S_DEAD)
 #define IS_NOCMTIME(inode)	((inode)->i_flags & S_NOCMTIME)

---
base-commit: a48fa7efaf1161c1c898931fe4c7f0070964233a
change-id: 20230908-acl-fix-6f8f86930f32

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>