6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jann Horn <jannh@xxxxxxxxxx>
commit 21d1b618b6b9da46c5116c640ac4b1cc8d40d63a upstream.
Ensure the superblock is kept alive until we're done with iput().
Holding a reference to an inode is not allowed unless we ensure the
superblock stays alive, which fsnotify does by keeping the
watched_objects count elevated, so iput() must happen before the
watched_objects decrement.
This can lead to a UAF of something like sb->s_fs_info in tmpfs, but the
UAF is hard to hit because race orderings that oops are more likely, thanks
to the CHECK_DATA_CORRUPTION() block in generic_shutdown_super().
Also, ensure that fsnotify_put_sb_watched_objects() doesn't call
fsnotify_sb_watched_objects() on a superblock that may have already been
freed, which would cause a UAF read of sb->s_fsnotify_info.
Cc: stable@xxxxxxxxxx
Fixes: d2f277e26f52 ("fsnotify: rename fsnotify_{get,put}_sb_connectors()")
Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/notify/mark.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -138,8 +138,11 @@ static void fsnotify_get_sb_watched_obje
static void fsnotify_put_sb_watched_objects(struct super_block *sb)
{
- if (atomic_long_dec_and_test(fsnotify_sb_watched_objects(sb)))
- wake_up_var(fsnotify_sb_watched_objects(sb));
+ atomic_long_t *watched_objects = fsnotify_sb_watched_objects(sb);
+
+ /* the superblock can go away after this decrement */
+ if (atomic_long_dec_and_test(watched_objects))
+ wake_up_var(watched_objects);
}
static void fsnotify_get_inode_ref(struct inode *inode)
@@ -150,8 +153,11 @@ static void fsnotify_get_inode_ref(struc
static void fsnotify_put_inode_ref(struct inode *inode)
{
- fsnotify_put_sb_watched_objects(inode->i_sb);
+ /* read ->i_sb before the inode can go away */
+ struct super_block *sb = inode->i_sb;
+
iput(inode);
+ fsnotify_put_sb_watched_objects(sb);
}
/*
