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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D8F19C433EF for ; Fri, 22 Oct 2021 16:25:45 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 5C5C561183 for ; Fri, 22 Oct 2021 16:25:45 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 5C5C561183 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=pwning.systems Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 8EB65900003; Fri, 22 Oct 2021 12:25:44 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 87493900002; Fri, 22 Oct 2021 12:25:44 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 73C4D900003; Fri, 22 Oct 2021 12:25:44 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0226.hostedemail.com [216.40.44.226]) by kanga.kvack.org (Postfix) with ESMTP id 63430900002 for ; Fri, 22 Oct 2021 12:25:44 -0400 (EDT) Received: from smtpin32.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 2889F8249980 for ; Fri, 22 Oct 2021 16:25:44 +0000 (UTC) X-FDA: 78724599408.32.990C5F3 Received: from MTA-06-4.privateemail.com (mta-06-4.privateemail.com [198.54.122.56]) by imf21.hostedemail.com (Postfix) with ESMTP id 56D10D035190 for ; Fri, 22 Oct 2021 16:25:41 +0000 (UTC) Received: from mta-06.privateemail.com (localhost [127.0.0.1]) by mta-06.privateemail.com (Postfix) with ESMTP id 0130218000A0; Fri, 22 Oct 2021 12:25:42 -0400 (EDT) Received: from APP-03 (unknown [10.50.14.153]) by mta-06.privateemail.com (Postfix) with ESMTPA id B938318000A2; Fri, 22 Oct 2021 12:25:41 -0400 (EDT) Date: Fri, 22 Oct 2021 12:25:41 -0400 (EDT) From: Jordy Zomer To: Dmitry Vyukov , syzbot , Mike Rapoport Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzkaller-bugs@googlegroups.com Message-ID: <1491925661.1465925.1634919941738@privateemail.com> In-Reply-To: References: <00000000000062d0fc05cef24c57@google.com> Subject: Re: [syzbot] WARNING: refcount bug in sys_memfd_secret MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Priority: 3 Importance: Normal X-Mailer: Open-Xchange Mailer v7.10.5-Rev24 X-Originating-Client: open-xchange-appsuite X-Virus-Scanned: ClamAV using ClamSMTP X-Stat-Signature: 3x8wpgj1u9s3f6mf3w5ej7eq8zck5zxj X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 56D10D035190 Authentication-Results: imf21.hostedemail.com; dkim=none; dmarc=none; spf=none (imf21.hostedemail.com: domain of jordy@pwning.systems has no SPF policy when checking 198.54.122.56) smtp.mailfrom=jordy@pwning.systems X-HE-Tag: 1634919941-597849 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: After a quick scan, it appears to be a false-positive. This because nothing appears to be being freed. In any case, you probably don't want warnings everywhere. I believe we should probably do something along the lines of: if (refcount_read(&secretmem_users) == 0) { refcount_set(&secretmem_users, 1); } else { refcount_inc(&secretmem_users); } Does this appear to be a feasible patch? :) Best Regards, Jordy > On 10/22/2021 11:07 AM Dmitry Vyukov wrote: > > > On Fri, 22 Oct 2021 at 17:02, syzbot > wrote: > > > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 64222515138e Merge tag 'drm-fixes-2021-10-22' of git://ano.. > > git tree: upstream > > console output: https://syzkaller.appspot.com/x/log.txt?x=178e86c4b00000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=be398dd7862f4b36 > > dashboard link: https://syzkaller.appspot.com/bug?extid=b904a1de3ec43711eba5 > > compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2 > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > Reported-by: syzbot+b904a1de3ec43711eba5@syzkaller.appspotmail.com > > +Mike, Jordy for secretmem.c > > > ------------[ cut here ]------------ > > refcount_t: addition on 0; use-after-free. > > WARNING: CPU: 2 PID: 32193 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25 > > Modules linked in: > > CPU: 2 PID: 32193 Comm: syz-executor.0 Not tainted 5.15.0-rc6-syzkaller #0 > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014 > > RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25 > > Code: 09 31 ff 89 de e8 f7 b9 9b fd 84 db 0f 85 36 ff ff ff e8 3a b2 9b fd 48 c7 c7 c0 65 e3 89 c6 05 6f 6c 7f 09 01 e8 7e 4a 19 05 <0f> 0b e9 17 ff ff ff e8 1b b2 9b fd 0f b6 1d 54 6c 7f 09 31 ff 89 > > RSP: 0018:ffffc90009f9ff10 EFLAGS: 00010286 > > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > > RDX: 0000000000040000 RSI: ffffffff815dbf58 RDI: fffff520013f3fd4 > > RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000001 > > R10: ffffffff815d5cce R11: 0000000000000000 R12: 0000000000000000 > > R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 > > FS: 00007f476a1e7700(0000) GS:ffff88802cd00000(0000) knlGS:0000000000000000 > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > CR2: 0000001b32c24000 CR3: 00000000494c4000 CR4: 0000000000150ee0 > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > > Call Trace: > > __refcount_add include/linux/refcount.h:199 [inline] > > __refcount_inc include/linux/refcount.h:250 [inline] > > refcount_inc include/linux/refcount.h:267 [inline] > > __do_sys_memfd_secret mm/secretmem.c:221 [inline] > > __se_sys_memfd_secret mm/secretmem.c:194 [inline] > > __x64_sys_memfd_secret+0x182/0x1e0 mm/secretmem.c:194 > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80 > > entry_SYSCALL_64_after_hwframe+0x44/0xae > > RIP: 0033:0x7f476cc71a39 > > Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48 > > RSP: 002b:00007f476a1e7188 EFLAGS: 00000246 ORIG_RAX: 00000000000001bf > > RAX: ffffffffffffffda RBX: 00007f476cd74f60 RCX: 00007f476cc71a39 > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 > > RBP: 00007f476cccbe8f R08: 0000000000000000 R09: 0000000000000000 > > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 > > R13: 00007ffc5b5eb85f R14: 00007f476a1e7300 R15: 0000000000022000 > > > > > > --- > > This report is generated by a bot. It may contain errors. > > See https://goo.gl/tpsmEJ for more information about syzbot. > > syzbot engineers can be reached at syzkaller@googlegroups.com. > > > > syzbot will keep track of this issue. See: > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot. > > > > -- > > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group. > > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@googlegroups.com. > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/00000000000062d0fc05cef24c57%40google.com.