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Date:   Sun, 12 Apr 2020 22:25:33 +0200
From:   Eugene Syromiatnikov <>
        Christian Brauner <>
Cc:     Andrew Morton <>,
        Ingo Molnar <>, Tejun Heo <>,
        Oleg Nesterov <>,
        Johannes Weiner <>,
        Li Zefan <>,
        Peter Zijlstra <>,,
        "Dmitry V. Levin" <>
Subject: [PATCH] clone3: fix cgroup argument sanity check

Checking that cgroup field value of struct clone_args is less than 0
is useless, as it is defined as unsigned 64-bit integer.  Moreover,
it doesn't catch the situations where its higher bits are lost during
the assignment to the cgroup field of the cgroup field of the internal
struct kernel_clone_args (where it is declared as signed 32-bit
integer), so it is still possible to pass garbage there.  A check
against INT_MAX solves both these issues.

Fixes: ef2c41cf38a7559b ("clone3: allow spawning processes into cgroups")
Signed-off-by: Eugene Syromiatnikov <>
 kernel/fork.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 4385f3d..b4f7775 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2631,7 +2631,7 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 		return -EINVAL;
-	if ((args.flags & CLONE_INTO_CGROUP) && args.cgroup < 0)
+	if ((args.flags & CLONE_INTO_CGROUP) && args.cgroup > INT_MAX)
 		return -EINVAL;
 	*kargs = (struct kernel_clone_args){

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