From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E0555C43331 for ; Mon, 11 Nov 2019 04:19:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B305120818 for ; Mon, 11 Nov 2019 04:19:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726756AbfKKET1 convert rfc822-to-8bit (ORCPT ); Sun, 10 Nov 2019 23:19:27 -0500 Received: from smtpbgsg2.qq.com ([54.254.200.128]:54395 "EHLO smtpbgsg2.qq.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726754AbfKKET1 (ORCPT ); Sun, 10 Nov 2019 23:19:27 -0500 X-QQ-mid: bizesmtp17t1573445961tabenr2u Received: from [192.168.142.168] (unknown [218.76.23.26]) by esmtp6.qq.com (ESMTP) with id ; Mon, 11 Nov 2019 12:19:20 +0800 (CST) X-QQ-SSF: 00400000002000T0ZU90000A0000000 X-QQ-FEAT: 8EH74LRXnGwJzwqDgsyfOqBPv3P3CAci3xmrrqnBF3su//jSAMhEwHWT26yQc p3h2HVX/itw2/exXsMqDreZ5oqqP6CYc+otEWFIwbaNfKygofZO5ww2htDFFMRiObiHh5Q7 JK+L9qj5Innb9w0PqmHMIxrp7GxFiMiVd/wsZHP7odTZ7ulOyDvgxwYh5AYofZbmWnT5tZN Jm+lqHfYRViVQ0o/xCNODRWVKv35K9Vi20o9LcffwJAfnm47/i3zkbUP4NzA8XUL+578umZ KCBSf7pQWrYjUIWtYJzb66frUc0nT8ORgof2qEsOJ4qQttsgzDhJXcciQoTYhC3taNJwQX2 VCw6E2NboleX9EJCwlqEmct7z0Vfg== X-QQ-GoodBg: 2 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.0 \(3601.0.10\)) Subject: Re: [PATCH] io_uring: fix error clear of ->file_table in io_sqe_files_register() From: Jackie Liu In-Reply-To: <834e83ff-e03c-24a0-0f50-1995d944056a@kernel.dk> Date: Mon, 11 Nov 2019 12:19:19 +0800 Cc: Bob Liu , io-uring@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: <5F7B4358-5805-4D83-AE99-5222A109B68D@kylinos.cn> References: <9851837d-47f3-abfe-8c19-f518e0935b22@kernel.dk> <834e83ff-e03c-24a0-0f50-1995d944056a@kernel.dk> To: Jens Axboe X-Mailer: Apple Mail (2.3601.0.10) X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:kylinos.cn:qybgforeign:qybgforeign7 X-QQ-Bgrelay: 1 Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org > 2019年11月11日 12:09，Jens Axboe 写道： > > On 11/10/19 9:02 PM, Jackie Liu wrote: >> >> >>> 2019年11月11日 11:54，Jens Axboe 写道： >>> >>> On 11/10/19 4:44 PM, Bob Liu wrote: >>>> On 11/10/19 11:46 PM, Jens Axboe wrote: >>>>> syzbot reports that when using failslab and friends, we can get a double >>>>> free in io_sqe_files_unregister(): >>>>> >>>>> BUG: KASAN: double-free or invalid-free in >>>>> io_sqe_files_unregister+0x20b/0x300 fs/io_uring.c:3185 >>>>> >>>>> CPU: 1 PID: 8819 Comm: syz-executor452 Not tainted 5.4.0-rc6-next-20191108 >>>>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS >>>>> Google 01/01/2011 >>>>> Call Trace: >>>>> __dump_stack lib/dump_stack.c:77 [inline] >>>>> dump_stack+0x197/0x210 lib/dump_stack.c:118 >>>>> print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374 >>>>> kasan_report_invalid_free+0x65/0xa0 mm/kasan/report.c:468 >>>>> __kasan_slab_free+0x13a/0x150 mm/kasan/common.c:450 >>>>> kasan_slab_free+0xe/0x10 mm/kasan/common.c:480 >>>>> __cache_free mm/slab.c:3426 [inline] >>>>> kfree+0x10a/0x2c0 mm/slab.c:3757 >>>>> io_sqe_files_unregister+0x20b/0x300 fs/io_uring.c:3185 >>>>> io_ring_ctx_free fs/io_uring.c:3998 [inline] >>>>> io_ring_ctx_wait_and_kill+0x348/0x700 fs/io_uring.c:4060 >>>>> io_uring_release+0x42/0x50 fs/io_uring.c:4068 >>>>> __fput+0x2ff/0x890 fs/file_table.c:280 >>>>> ____fput+0x16/0x20 fs/file_table.c:313 >>>>> task_work_run+0x145/0x1c0 kernel/task_work.c:113 >>>>> exit_task_work include/linux/task_work.h:22 [inline] >>>>> do_exit+0x904/0x2e60 kernel/exit.c:817 >>>>> do_group_exit+0x135/0x360 kernel/exit.c:921 >>>>> __do_sys_exit_group kernel/exit.c:932 [inline] >>>>> __se_sys_exit_group kernel/exit.c:930 [inline] >>>>> __x64_sys_exit_group+0x44/0x50 kernel/exit.c:930 >>>>> do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290 >>>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe >>>>> RIP: 0033:0x43f2c8 >>>>> Code: 31 b8 c5 f7 ff ff 48 8b 5c 24 28 48 8b 6c 24 30 4c 8b 64 24 38 4c 8b >>>>> 6c 24 40 4c 8b 74 24 48 4c 8b 7c 24 50 48 83 c4 58 c3 66 <0f> 1f 84 00 00 >>>>> 00 00 00 48 8d 35 59 ca 00 00 0f b6 d2 48 89 fb 48 >>>>> RSP: 002b:00007ffd5b976008 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 >>>>> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000043f2c8 >>>>> RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000 >>>>> RBP: 00000000004bf0a8 R08: 00000000000000e7 R09: ffffffffffffffd0 >>>>> R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000001 >>>>> R13: 00000000006d1180 R14: 0000000000000000 R15: 0000000000000000 >>>>> >>>>> This happens if we fail allocating the file tables. For that case we do >>>>> free the file table correctly, but we forget to set it to NULL. This >>>>> means that ring teardown will see it as being non-NULL, and attempt to >>>>> free it again. >>>>> >>>>> Fix this by clearing the file_table pointer if we free the table. >>>>> >>>>> Reported-by: syzbot+3254bc44113ae1e331ee@syzkaller.appspotmail.com >>>>> Fixes: 65e19f54d29c ("io_uring: support for larger fixed file sets") >>>>> Signed-off-by: Jens Axboe >>>>> >>>> >>>> Reviewed-by: Bob Liu >>> >>> Thanks, added. >>> >>>> By the way, there are many place(besides io_uring.c) which need to set >>>> pointer to NULL after free. I saw similar fix from time to time. >>>> >>>> Do you think a safe_free() is worth? e.g >>>> #define SAFE_FREE(p) { if (p) { free(p); (p)=NULL; } } >>> >>> Hmm not sure, and would probably be better as: >>> >>> kfree_safe(&ptr); >>> >>> or something instead. I seem to recall discussions about that ages ago, >>> probably worth while to try and search and see if you can find those. I >>> suspect Linus hates it, reasons not remembered ;-) >>> >> >> I think this may be a worthwhile solution, but kfree can handle NULL, we can >> set it to NULL directly after free is finished. >> >> void kfree_safe(const void *ptr) >> { >> kfree(ptr); >> ptr = NULL; >> } > > Sure, but that doesn't change the ptr in the caller, which was my point. > You need to pass in a pointer to the pointer for that, otherwise > clearing it in kfree_safe() is pointless: > > void kfree_safe(const void **ptr) > { > kfree(*ptr); > *ptr = NULL; > } Yes, you are right. If it is set to NULL directly, if it is wrong, it can be panic immediately, which is convenient for debugging. > > and then you run into all sorts of fun, since void ** isn't the same as > 'struct foo **'. > -- BR, Jackie Liu