[PATCH] clone3: fix cgroup argument sanity check

[PATCH] clone3: fix cgroup argument sanity check

[Eugene Syromiatnikov]

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 <esyr@redhat.com>
---
 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,
 		     !valid_signal(args.exit_signal)))
 		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){
-- 
2.1.4

Re: [PATCH] clone3: fix cgroup argument sanity check

[Christian Brauner]

On Sun, Apr 12, 2020 at 10:25:33PM +0200, Eugene Syromiatnikov wrote:
> 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 <esyr@redhat.com>

Thanks, will queue for rc2 unless I hear objections.
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Re: [PATCH] clone3: fix cgroup argument sanity check

[Christian Brauner]

On Sun, Apr 12, 2020 at 10:25:33PM +0200, Eugene Syromiatnikov wrote:
> 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 <esyr@redhat.com>
> Acked-by: Christian Brauner <christian.brauner@ubuntu.com>

Applied, thanks!
Christian