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 D11F8C43331 for ; Mon, 11 Nov 2019 04:02:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A6FB220869 for ; Mon, 11 Nov 2019 04:02:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726765AbfKKECZ convert rfc822-to-8bit (ORCPT ); Sun, 10 Nov 2019 23:02:25 -0500 Received: from smtpbgeu1.qq.com ([52.59.177.22]:39660 "EHLO smtpbgeu1.qq.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726754AbfKKECZ (ORCPT ); Sun, 10 Nov 2019 23:02:25 -0500 X-QQ-mid: bizesmtp28t1573444937t9vxn0zl Received: from [192.168.142.168] (unknown [218.76.23.26]) by esmtp10.qq.com (ESMTP) with id ; Mon, 11 Nov 2019 12:02:17 +0800 (CST) X-QQ-SSF: 00400000002000T0ZU90000A0000000 X-QQ-FEAT: CBgi6aaeY4evjhUV7XE6oyTYxynq5/24tfZ9Tpvnd2brX7nuwWuCOlg0MZNz3 nO2Xt7RKFjEHHc0TMPMxhFOx/AgbElTMj/CKFZGcoM8MOoC4YH3axGemx8BeVLRq4r2mxmi 1zhufdCJ329KCvDScLZzSAmf/rVmBgLEv0YZ9kPPCXCGcAoMPyzJatfe1w7d3wB1eOMOf/I mmY0hXYF/JZwBIwwqT2r4XlMcfb8bo8/qcjEL3bcloyIOkeAKt40TUt7MHNtcuWySow9yYZ 7E2rZAE2R22TrCi2Y9Huzo0nxRuVqylJMgei+FXIL8UcPLQfXbjHYvTnEMAvEPm0cVrASWz CcfGs2eSBhNgZ1WUiLDeSKxvTqtjQ== 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: Date: Mon, 11 Nov 2019 12:02:16 +0800 Cc: Bob Liu , io-uring@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: References: <9851837d-47f3-abfe-8c19-f518e0935b22@kernel.dk> To: Jens Axboe X-Mailer: Apple Mail (2.3601.0.10) X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:kylinos.cn:qybgforeign:qybgforeign5 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 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; } -- BR, Jackie Liu