[PATCH] fs: drop peer group ids under namespace lock

[PATCH] fs: drop peer group ids under namespace lock

[Christian Brauner]

When cleaning up peer group ids in the failure path we need to make sure
to hold on to the namespace lock. Otherwise another thread might just
turn the mount from a shared into a non-shared mount concurrently.

Reported-by: syzbot+8ac3859139c685c4f597@syzkaller.appspotmail.com
Link: https://lore.kernel.org/lkml/00000000000088694505f8132d77@google.com
Fixes: 2a1867219c7b ("fs: add mount_setattr()")
Cc: stable@vger.kernel.org # 5.12+
Signed-off-by: Christian Brauner <brauner@kernel.org>
---
 fs/namespace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/namespace.c b/fs/namespace.c
index bc0f15257b49..6836e937ee61 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -4183,9 +4183,9 @@ static int do_mount_setattr(struct path *path, struct mount_kattr *kattr)
 	unlock_mount_hash();
 
 	if (kattr->propagation) {
-		namespace_unlock();
 		if (err)
 			cleanup_group_ids(mnt, NULL);
+		namespace_unlock();
 	}
 
 	return err;

---
base-commit: 197b6b60ae7bc51dd0814953c562833143b292aa
change-id: 20230330-vfs-mount_setattr-propagation-fix-363b7c59d7fb

Re: [PATCH] fs: drop peer group ids under namespace lock

[Christian Brauner]

On Thu, 30 Mar 2023 09:13:16 +0200, Christian Brauner wrote:
> When cleaning up peer group ids in the failure path we need to make sure
> to hold on to the namespace lock. Otherwise another thread might just
> turn the mount from a shared into a non-shared mount concurrently.
> 
> 

Ok, syzbot is happy with this as well so let's get this fixed and backported,

tree: git://git.kernel.org/pub/scm/linux/kernel/git/vfs/idmapping.git
branch: vfs.misc.fixes
[1/1] fs: drop peer group ids under namespace lock
      commit: cb2239c198ad9fbd5aced22cf93e45562da781eb