[PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts_overlimit

From: "Eric W. Biederman" <ebiederm@xmission.com>
To: linux-kernel@vger.kernel.org
Cc: "Alexey Gladkov" <legion@kernel.org>,
	"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>,
	containers@lists.linux-foundation.org,
	"Michal Koutný" <mkoutny@suse.com>,
	linux-api@vger.kernel.org,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	stable@vger.kernel.org
Subject: [PATCH v2 5/5] ucounts: Handle wrapping in is_ucounts_overlimit
Date: Wed, 16 Feb 2022 09:58:32 -0600	[thread overview]
Message-ID: <20220216155832.680775-5-ebiederm@xmission.com> (raw)
In-Reply-To: <87ilteiz4a.fsf_-_@email.froward.int.ebiederm.org>

While examining is_ucounts_overlimit and reading the various messages
I realized that is_ucounts_overlimit fails to deal with counts that
may have wrapped.

Being wrapped should be a transitory state for counts and they should
never be wrapped for long, but it can happen so handle it.

Cc: stable@vger.kernel.org
Fixes: 21d1c5e386bc ("Reimplement RLIMIT_NPROC on top of ucounts")
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 kernel/ucount.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 65b597431c86..06ea04d44685 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -350,7 +350,8 @@ bool is_ucounts_overlimit(struct ucounts *ucounts, enum ucount_type type, unsign
 	if (rlimit > LONG_MAX)
 		max = LONG_MAX;
 	for (iter = ucounts; iter; iter = iter->ns->ucounts) {
-		if (get_ucounts_value(iter, type) > max)
+		long val = get_ucounts_value(iter, type);
+		if (val < 0 || val > max)
 			return true;
 		max = READ_ONCE(iter->ns->ucount_max[type]);
 	}
-- 
2.29.2

