Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   =?UTF-8?q?Michal=20Koutn=C3=BD?= <mkoutny@suse.com>
To:     Eric Biederman <ebiederm@xmission.com>,
        Alexey Gladkov <legion@kernel.org>
Cc:     Kees Cook <keescook@chromium.org>, Shuah Khan <shuah@kernel.org>,
        Christian Brauner <brauner@kernel.org>,
        Solar Designer <solar@openwall.com>,
        Ran Xiaokai <ran.xiaokai@zte.com.cn>,
        linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        Linux Containers <containers@lists.linux-foundation.org>
Subject: [RFC PATCH 1/6] set_user: Perform RLIMIT_NPROC capability check against new user credentials
Date:   Mon,  7 Feb 2022 13:17:55 +0100
Message-Id: <20220207121800.5079-2-mkoutny@suse.com>
In-Reply-To: <20220207121800.5079-1-mkoutny@suse.com>
References: <20220207121800.5079-1-mkoutny@suse.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Precedence: bulk

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@openwall.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Michal Koutný <mkoutny@suse.com>
---
 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