From nobody Wed Apr 8 06:03:34 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 24124C28D13 for ; Tue, 23 Aug 2022 00:49:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237759AbiHWAtS (ORCPT ); Mon, 22 Aug 2022 20:49:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46748 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239189AbiHWAss (ORCPT ); Mon, 22 Aug 2022 20:48:48 -0400 Received: from smtp-fw-80006.amazon.com (smtp-fw-80006.amazon.com [99.78.197.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B573B49B74 for ; Mon, 22 Aug 2022 17:48:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1661215723; x=1692751723; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=s3kBGZYJKBSjf+d5HPTRJJuTKSq36UjTQpNEdBAnad8=; b=p0iJdjMQsfSx5WZ9R9PGLtMYgkM9AZPj7cCugQeo+i7arnGmWDSfm5+G XKGBijbRLe7zLcMgY2cv6R1Tk0RgNbz0DVXr8TPn3msHkuW4z8aB2L6YL vJ79BqDsHhnHo/dPhghw1Fja7qpLIdk7ORZfSQd+lKD8mtm2CxVTWYvFI U=; X-IronPort-AV: E=Sophos;i="5.93,256,1654560000"; d="scan'208";a="122262419" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1d-f20e0c8b.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-80006.pdx80.corp.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 23 Aug 2022 00:48:26 +0000 Received: from EX13MTAUWB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1d-f20e0c8b.us-east-1.amazon.com (Postfix) with ESMTPS id 4E28D81875; Tue, 23 Aug 2022 00:48:24 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX13MTAUWB001.ant.amazon.com (10.43.161.249) with Microsoft SMTP Server (TLS) id 15.0.1497.38; Tue, 23 Aug 2022 00:48:22 +0000 Received: from 88665a182662.ant.amazon.com (10.43.160.191) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.1118.12; Tue, 23 Aug 2022 00:48:20 +0000 From: Kuniyuki Iwashima To: Kees Cook , Andy Lutomirski , Will Drewry CC: Christian Brauner , Kuniyuki Iwashima , Kuniyuki Iwashima , , , Ayushman Dutta Subject: [PATCH v2] seccomp: Move copy_seccomp() to no failure path. Date: Mon, 22 Aug 2022 17:48:06 -0700 Message-ID: <20220823004806.38681-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.43.160.191] X-ClientProxiedBy: EX13D34UWA004.ant.amazon.com (10.43.160.177) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Our syzbot instance reported memory leaks in do_seccomp() [0], similar to the report [1]. It shows that we miss freeing struct seccomp_filter and some objects included in it. We can reproduce the issue with the program below [2] which calls one seccomp() and two clone() syscalls. The first clone()d child exits earlier than its parent and sends a signal to kill it during the second clone(), more precisely before the fatal_signal_pending() test in copy_process(). When the parent receives the signal, it has to destroy the embryonic process and return -EINTR to user space. In the failure path, we have to call seccomp_filter_release() to decrement the filter's refcount. Initially, we called it in free_task() called from the failure path, but the commit 3a15fb6ed92c ("seccomp: release filter after task is fully dead") moved it to release_task() to notify user space as early as possible that the filter is no longer used. To keep the change and current seccomp refcount semantics, let's move copy_seccomp() just after the signal check and add a WARN_ON_ONCE() in free_task() for future debugging. [0]: unreferenced object 0xffff8880063add00 (size 256): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.914s) hex dump (first 32 bytes): 01 00 00 00 01 00 00 00 00 00 00 00 00 00 00 00 ................ ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................ backtrace: do_seccomp (./include/linux/slab.h:600 ./include/linux/slab.h:733 kerne= l/seccomp.c:666 kernel/seccomp.c:708 kernel/seccomp.c:1871 kernel/seccomp.c= :1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffffc90000035000 (size 4096): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 32 bytes): 01 00 00 00 00 00 00 00 00 00 00 00 05 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: __vmalloc_node_range (mm/vmalloc.c:3226) __vmalloc_node (mm/vmalloc.c:3261 (discriminator 4)) bpf_prog_alloc_no_stats (kernel/bpf/core.c:91) bpf_prog_alloc (kernel/bpf/core.c:129) bpf_prog_create_from_user (net/core/filter.c:1414) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:= 1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffff888003fa1000 (size 1024): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ backtrace: bpf_prog_alloc_no_stats (./include/linux/slab.h:600 ./include/linux/sla= b.h:733 kernel/bpf/core.c:95) bpf_prog_alloc (kernel/bpf/core.c:129) bpf_prog_create_from_user (net/core/filter.c:1414) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:= 1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffff888006360240 (size 16): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 16 bytes): 01 00 37 00 76 65 72 6c e0 83 01 06 80 88 ff ff ..7.verl........ backtrace: bpf_prog_store_orig_filter (net/core/filter.c:1137) bpf_prog_create_from_user (net/core/filter.c:1428) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:= 1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) unreferenced object 0xffff8880060183e0 (size 8): comm "repro_seccomp", pid 230, jiffies 4294687090 (age 9.915s) hex dump (first 8 bytes): 06 00 00 00 00 00 ff 7f ........ backtrace: kmemdup (mm/util.c:129) bpf_prog_store_orig_filter (net/core/filter.c:1144) bpf_prog_create_from_user (net/core/filter.c:1428) do_seccomp (kernel/seccomp.c:671 kernel/seccomp.c:708 kernel/seccomp.c:= 1871 kernel/seccomp.c:1991) do_syscall_64 (arch/x86/entry/common.c:50 arch/x86/entry/common.c:80) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) [1]: https://syzkaller.appspot.com/bug?id=3D2809bb0ac77ad9aa3f4afe42d6a610a= ba594a987 [2]: #define _GNU_SOURCE #include #include #include #include #include #include void main(void) { struct sock_filter filter[] =3D { BPF_STMT(BPF_RET | BPF_K, SECCOMP_RET_ALLOW), }; struct sock_fprog fprog =3D { .len =3D sizeof(filter) / sizeof(filter[0]), .filter =3D filter, }; long i, pid; syscall(__NR_seccomp, SECCOMP_SET_MODE_FILTER, 0, &fprog); for (i =3D 0; i < 2; i++) { pid =3D syscall(__NR_clone, CLONE_NEWNET | SIGKILL, NULL, NULL, 0); if (pid =3D=3D 0) return; } } Fixes: 3a15fb6ed92c ("seccomp: release filter after task is fully dead") Reported-by: syzbot+ab17848fe269b573eb71@syzkaller.appspotmail.com Reported-by: Ayushman Dutta Suggested-by: Kees Cook Signed-off-by: Kuniyuki Iwashima Reported-by: kernel test robot Reviewed-by: Christian Brauner (Microsoft) --- v2: * Move copy_seccomp() after no failure path instead of adding seccomp_filter_release() in the failure path. v1: https://lore.kernel.org/lkml/20220822204436.26631-1-kuniyu@amazon.com/ --- kernel/fork.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 90c85b17bf69..21c7365c8322 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -537,6 +537,7 @@ void put_task_stack(struct task_struct *tsk) =20 void free_task(struct task_struct *tsk) { + WARN_ON_ONCE(tsk->seccomp.filter); release_user_cpus_ptr(tsk); scs_release(tsk); =20 @@ -2409,12 +2410,6 @@ static __latent_entropy struct task_struct *copy_pro= cess( =20 spin_lock(¤t->sighand->siglock); =20 - /* - * Copy seccomp details explicitly here, in case they were changed - * before holding sighand lock. - */ - copy_seccomp(p); - rv_task_fork(p); =20 rseq_fork(p, clone_flags); @@ -2431,6 +2426,14 @@ static __latent_entropy struct task_struct *copy_pro= cess( goto bad_fork_cancel_cgroup; } =20 + /* No more failure paths after this point. */ + + /* + * Copy seccomp details explicitly here, in case they were changed + * before holding sighand lock. + */ + copy_seccomp(p); + init_task_pid_links(p); if (likely(p->pid)) { ptrace_init_task(p, (clone_flags & CLONE_PTRACE) || trace); --=20 2.30.2