[PATCH] fs/super: fix s_fs_info leak when setup_bdev_super() fails

[Shardul Bankar <shardulsb08@gmail.com>]

In get_tree_bdev_flags(), sget_dev() calls sget_fc(), which transfers
ownership of fc->s_fs_info to the new superblock (s->s_fs_info) and
clears fc->s_fs_info. If setup_bdev_super() then fails, the superblock
is torn down via deactivate_locked_super(). However,
generic_shutdown_super() only calls the filesystem's ->put_super()
when sb->s_root is non-NULL. Since setup_bdev_super() fails before
fill_super() runs, sb->s_root is never set, so ->put_super() is never
called and the allocated s_fs_info is leaked.

Return ownership of s_fs_info to fc when setup_bdev_super() fails so
put_fs_context() can free it via the filesystem's ->free() callback.
Clear s->s_fs_info to avoid a stale reference. Do this only when
setup_bdev_super() fails; when fill_super() fails, it already frees
s_fs_info in its own error path.

Reported-by: syzbot+99f6ed51479b86ac4c41@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=99f6ed51479b86ac4c41
Signed-off-by: Shardul Bankar <shardul.b@mpiricsoftware.com>
---
 fs/super.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index 3d85265d1400..1aa8dbd19bb6 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1687,6 +1687,11 @@ int get_tree_bdev_flags(struct fs_context *fc,
 		}
 	} else {
 		error = setup_bdev_super(s, fc->sb_flags, fc);
+		if (error) {
+			fc->s_fs_info = s->s_fs_info;
+			s->s_fs_info = NULL;
+		}
+
 		if (!error)
 			error = fill_super(s, fc);
 		if (error) {
-- 
2.34.1