From: Eugene Syromiatnikov <esyr@redhat.com>
To: linux-kernel@vger.kernel.org,
Christian Brauner <christian@brauner.io>,
Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
"Dmitry V. Levin" <ldv@altlinux.org>,
Eric Biederman <ebiederm@xmission.com>
Subject: [PATCH v3] fork: check exit_signal passed in clone3() call
Date: Wed, 11 Sep 2019 18:45:40 +0100
Message-ID: <4b38fa4ce420b119a4c6345f42fe3cec2de9b0b5.1568223594.git.esyr@redhat.com> (raw)
In-Reply-To: <cover.1568223594.git.esyr@redhat.com>
Previously, higher 32 bits of exit_signal fields were lost when
copied to the kernel args structure (that uses int as a type for the
respective field). Moreover, as Oleg has noted[1], exit_signal is used
unchecked, so it has to be checked for sanity before use; for the legacy
syscalls, applying CSIGNAL mask guarantees that it is at least non-negative;
however, there's no such thing is done in clone3() code path, and that can
break at least thread_group_leader.
Adding checks that user-passed exit_signal fits into int and passes
valid_signal() check solves both of these problems.
[1] https://lkml.org/lkml/2019/9/10/467
* kernel/fork.c (copy_clone_args_from_user): Fail with -EINVAL if
args.exit_signal is greater than UINT_MAX or is not a valid signal.
(_do_fork): Note that exit_signal is expected to be checked for the
sanity by the caller.
Fixes: 7f192e3cd316 ("fork: add clone3")
Reported-by: Oleg Nesterov <oleg@redhat.com>
Co-authored-by: Oleg Nesterov <oleg@redhat.com>
Co-authored-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
---
kernel/fork.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/kernel/fork.c b/kernel/fork.c
index 2852d0e..f98314b 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2338,6 +2338,8 @@ struct mm_struct *copy_init_mm(void)
*
* It copies the process, and if successful kick-starts
* it and waits for it to finish using the VM if required.
+ *
+ * args->exit_signal is expected to be checked for sanity by the caller.
*/
long _do_fork(struct kernel_clone_args *args)
{
@@ -2562,6 +2564,15 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
if (copy_from_user(&args, uargs, size))
return -EFAULT;
+ /*
+ * Two separate checks are needed, as valid_signal() takes unsigned long
+ * as an argument, and struct kernel_clone_args uses int type
+ * for the exit_signal field.
+ */
+ if (unlikely((args.exit_signal > UINT_MAX) ||
+ !valid_signal(args.exit_signal)))
+ return -EINVAL;
+
*kargs = (struct kernel_clone_args){
.flags = args.flags,
.pidfd = u64_to_user_ptr(args.pidfd),
--
2.1.4
next prev parent reply index
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-11 17:45 Eugene Syromiatnikov
2019-09-11 17:45 ` Eugene Syromiatnikov [this message]
2019-09-12 16:51 ` Oleg Nesterov
2019-09-13 11:40 ` Christian Brauner
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