linux-kernel - [PATCH] clone3: add build-time CLONE_ARGS_SIZE

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Date:   Sun, 12 Apr 2020 22:26:58 +0200
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>, Tejun Heo <tj@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: [PATCH] clone3: add build-time CLONE_ARGS_SIZE_VER* validity checks

CLONE_ARGS_SIZE_VER* macros are defined explicitly and not via
the offsets of the relevant struct clone_args fields, which makes
it rather error-prone, so it probably makes sense to add some
compile-time checks for them (including the one that breaks
on struct clone_args extension as a reminder to add a relevant
size macro and a similar check).  Function copy_clone_args_from_user
seems to be a good place for such checks.

Signed-off-by: Eugene Syromiatnikov <esyr@...hat.com>
---
 kernel/fork.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/fork.c b/kernel/fork.c
index b4f7775..11bcc7e 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2605,6 +2605,14 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
 	struct clone_args args;
 	pid_t *kset_tid = kargs->set_tid;
 
+	BUILD_BUG_ON(offsetofend(struct clone_args, tls) !=
+		     CLONE_ARGS_SIZE_VER0);
+	BUILD_BUG_ON(offsetofend(struct clone_args, set_tid_size) !=
+		     CLONE_ARGS_SIZE_VER1);
+	BUILD_BUG_ON(offsetofend(struct clone_args, cgroup) !=
+		     CLONE_ARGS_SIZE_VER2);
+	BUILD_BUG_ON(sizeof(struct clone_args) != CLONE_ARGS_SIZE_VER2);
+
 	if (unlikely(usize > PAGE_SIZE))
 		return -E2BIG;
 	if (unlikely(usize < CLONE_ARGS_SIZE_VER0))
-- 
2.1.4