From 0014edaedfd804dbf35b009808789325ca615716 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Wed, 20 Apr 2022 15:19:25 +0200 Subject: fs: unset MNT_WRITE_HOLD on failure After mnt_hold_writers() has been called we will always have set MNT_WRITE_HOLD and consequently we always need to pair mnt_hold_writers() with mnt_unhold_writers(). After the recent cleanup in [1] where Al switched from a do-while to a for loop the cleanup currently fails to unset MNT_WRITE_HOLD for the first mount that was changed. Fix this and make sure that the first mount will be cleaned up and add some comments to make it more obvious. Link: https://lore.kernel.org/lkml/0000000000007cc21d05dd0432b8@google.com Link: https://lore.kernel.org/lkml/00000000000080e10e05dd043247@google.com Link: https://lore.kernel.org/r/20220420131925.2464685-1-brauner@kernel.org Fixes: e257039f0fc7 ("mount_setattr(): clean the control flow and calling conventions") [1] Cc: Hillf Danton Cc: Christoph Hellwig Cc: Al Viro Reported-by: syzbot+10a16d1c43580983f6a2@syzkaller.appspotmail.com Reported-by: syzbot+306090cfa3294f0bbfb3@syzkaller.appspotmail.com Reviewed-by: Christoph Hellwig Signed-off-by: Christian Brauner (Microsoft) --- fs/namespace.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/namespace.c b/fs/namespace.c index a0a36bfa3aa0..afe2b64b14f1 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -4058,10 +4058,22 @@ static int mount_setattr_prepare(struct mount_kattr *kattr, struct mount *mnt) if (err) { struct mount *p; - for (p = mnt; p != m; p = next_mnt(p, mnt)) { + /* + * If we had to call mnt_hold_writers() MNT_WRITE_HOLD will + * be set in @mnt_flags. The loop unsets MNT_WRITE_HOLD for all + * mounts and needs to take care to include the first mount. + */ + for (p = mnt; p; p = next_mnt(p, mnt)) { /* If we had to hold writers unblock them. */ if (p->mnt.mnt_flags & MNT_WRITE_HOLD) mnt_unhold_writers(p); + + /* + * We're done once the first mount we changed got + * MNT_WRITE_HOLD unset. + */ + if (p == m) + break; } } return err; -- cgit v1.2.3