Commit 795bb82d authored by Amir Goldstein's avatar Amir Goldstein Committed by Jan Kara
Browse files

fsnotify: fix UAF from FS_ERROR event on a shutting down filesystem 



Protect against use after free when filesystem calls fsnotify_sb_error()
during fs shutdown.

Move freeing of sb->s_fsnotify_info to destroy_super_work(), because it
may be accessed from fs shutdown context.

Reported-by: default avatar <syzbot+5e3f9b2a67b45f16d4e6@syzkaller.appspotmail.com>
Suggested-by: default avatarJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/linux-fsdevel/20240416173211.4lnmgctyo4jn5fha@quack3/


Fixes: 07a3b8d0 ("fsnotify: lazy attach fsnotify_sb_info state to sb")
Reviewed-by: default avatarChristian Brauner <brauner@kernel.org>
Signed-off-by: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Message-Id: <20240416181452.567070-1-amir73il@gmail.com>
parent a5e57b4d

fs/notify/fsnotify.c

+5 −1
Original line number Diff line number Diff line
@@ -103,7 +103,11 @@ void fsnotify_sb_delete(struct super_block *sb) 
	WARN_ON(fsnotify_sb_has_priority_watchers(sb, FSNOTIFY_PRIO_CONTENT));

	WARN_ON(fsnotify_sb_has_priority_watchers(sb,

						  FSNOTIFY_PRIO_PRE_CONTENT));

	kfree(sbinfo);

}



void fsnotify_sb_free(struct super_block *sb)

{

	kfree(sb->s_fsnotify_info);

}



/*

fs/super.c

+1 −0
Original line number Diff line number Diff line
@@ -274,6 +274,7 @@ static void destroy_super_work(struct work_struct *work) 
{

	struct super_block *s = container_of(work, struct super_block,

							destroy_work);

	fsnotify_sb_free(s);

	security_sb_free(s);

	put_user_ns(s->s_user_ns);

	kfree(s->s_subtype);

include/linux/fsnotify_backend.h

+4 −0
Original line number Diff line number Diff line
@@ -576,6 +576,7 @@ extern int __fsnotify_parent(struct dentry *dentry, __u32 mask, const void *data 
extern void __fsnotify_inode_delete(struct inode *inode);

extern void __fsnotify_vfsmount_delete(struct vfsmount *mnt);

extern void fsnotify_sb_delete(struct super_block *sb);

extern void fsnotify_sb_free(struct super_block *sb);

extern u32 fsnotify_get_cookie(void);



static inline __u32 fsnotify_parent_needed_mask(__u32 mask)
@@ -880,6 +881,9 @@ static inline void __fsnotify_vfsmount_delete(struct vfsmount *mnt) 
static inline void fsnotify_sb_delete(struct super_block *sb)

{}



static inline void fsnotify_sb_free(struct super_block *sb)

{}



static inline void fsnotify_update_flags(struct dentry *dentry)

{}