[PATCH 5.15 20/21] mm/mlock: fix potential imbalanced rlimit ucounts adjustment

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Miaohe Lin <linmiaohe@huawei.com>

commit 5c2a956c3eea173b2bc89f632507c0eeaebf6c4a upstream.

user_shm_lock forgets to set allowed to 0 when get_ucounts fails.  So
the later user_shm_unlock might do the extra dec_rlimit_ucounts.  Fix
this by resetting allowed to 0.

Link: https://lkml.kernel.org/r/20220310132417.41189-1-linmiaohe@huawei.com
Fixes: d7c9e99aee48 ("Reimplement RLIMIT_MEMLOCK on top of ucounts")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Herbert van den Bergh <herbert.van.den.bergh@oracle.com>
Cc: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/mlock.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -837,6 +837,7 @@ int user_shm_lock(size_t size, struct uc
 	}
 	if (!get_ucounts(ucounts)) {
 		dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
+		allowed = 0;
 		goto out;
 	}
 	allowed = 1;