[RFC PATCH 1/6] set_user: Perform RLIMIT_NPROC capability check against new user credentials

[Michal Koutný]

The check is currently against the current->cred but since those are
going to change and we want to check RLIMIT_NPROC condition after the
switch, supply the capability check with the new cred.
But since we're checking new_user being INIT_USER any new cred's
capability-based allowance may be redundant when the check fails and the
alternative solution would be revert of the commit 2863643fb8b9
("set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds")

Fixes: 2863643fb8b9 ("set_user: add capability check when rlimit(RLIMIT_NPROC) exceeds")

Cc: Solar Designer <solar@xxxxxxxxxxxx>
Cc: Christian Brauner <christian.brauner@xxxxxxxxxx>
Signed-off-by: Michal Koutný <mkoutny@xxxxxxxx>
---
 kernel/sys.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 8ea20912103a..48c90dcceff3 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -481,7 +481,8 @@ static int set_user(struct cred *new)
 	 */
 	if (ucounts_limit_cmp(new->ucounts, UCOUNT_RLIMIT_NPROC, rlimit(RLIMIT_NPROC)) >= 0 &&
 			new_user != INIT_USER &&
-			!capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN))
+			!security_capable(new, &init_user_ns, CAP_SYS_RESOURCE, CAP_OPT_NONE) &&
+			!security_capable(new, &init_user_ns, CAP_SYS_ADMIN, CAP_OPT_NONE))
 		current->flags |= PF_NPROC_EXCEEDED;
 	else
 		current->flags &= ~PF_NPROC_EXCEEDED;
-- 
2.34.1