linux-kernel - [PATCH][next] clone3: fix an unsigned args.cgroup comparison to less than zero

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Message-Id: <20200222001513.43099-1-colin.king@canonical.com>
Date:   Sat, 22 Feb 2020 00:15:13 +0000
From:   Colin King <colin.king@...onical.com>
To:     Christian Brauner <christian@...uner.io>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][next] clone3: fix an unsigned args.cgroup comparison to less than zero

From: Colin Ian King <colin.king@...onical.com>

The less than zero comparison of args.cgroup is aways false because
args.cgroup is a u64 and can never be less than zero.  I believe the
correct check is to cast args.cgroup to a s64 first to ensure an
invalid value is not copied to kargs->cgroup.

Addresses-Coverity: ("Unsigned compared against 0")
Fixes: ef2c41cf38a7 ("clone3: allow spawning processes into cgroups")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 kernel/fork.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 67a5d691ffa8..98513a122dd1 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2635,7 +2635,7 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 		     !valid_signal(args.exit_signal)))
 		return -EINVAL;
 
-	if ((args.flags & CLONE_INTO_CGROUP) && args.cgroup < 0)
+	if ((args.flags & CLONE_INTO_CGROUP) && (s64)args.cgroup < 0)
 		return -EINVAL;
 
 	*kargs = (struct kernel_clone_args){
-- 
2.25.0