Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754096AbdLDNr7 (ORCPT ); Mon, 4 Dec 2017 08:47:59 -0500 Received: from mail-pf0-f170.google.com ([209.85.192.170]:37352 "EHLO mail-pf0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752209AbdLDNr4 (ORCPT ); Mon, 4 Dec 2017 08:47:56 -0500 X-Google-Smtp-Source: AGs4zMbphNNLXap7c2yobJAEetciM7R3khev+ROg1nPnVZbVxwBIz2A40FOkiknYgBD1xXLDipZNSKdtO8HjtwMcp9c= MIME-Version: 1.0 In-Reply-To: <1512395025.20988.3.camel@tycho.nsa.gov> References: <001a113f711a721c58055f052200@google.com> <089e08259d282c063e055f4bddbd@google.com> <97d6bab0-d278-9945-5d82-a0a76b8b78c5@I-love.SAKURA.ne.jp> <1512395025.20988.3.camel@tycho.nsa.gov> From: Dmitry Vyukov Date: Mon, 4 Dec 2017 14:47:34 +0100 Message-ID: Subject: Re: KASAN: slab-out-of-bounds Read in strcmp To: Stephen Smalley Cc: Tetsuo Handa , syzbot , linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, syzkaller-bugs@googlegroups.com, LKML , dledford@redhat.com, Matthias Kaehlcke , junil0814.lee@lge.com, kyeongdon kim , Paul Moore Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2711 Lines: 70 On Mon, Dec 4, 2017 at 2:43 PM, Stephen Smalley wrote: > On Sun, 2017-12-03 at 20:33 +0900, Tetsuo Handa wrote: >> On 2017/12/02 3:52, syzbot wrote: >> > ================================================================== >> > BUG: KASAN: slab-out-of-bounds in strcmp+0x96/0xb0 lib/string.c:328 >> > Read of size 1 at addr ffff8801cd99d2c1 by task >> > syzkaller242593/3087 >> > >> > CPU: 0 PID: 3087 Comm: syzkaller242593 Not tainted 4.15.0-rc1-next- >> > 20171201+ #57 >> > Hardware name: Google Google Compute Engine/Google Compute Engine, >> > BIOS Google 01/01/2011 >> > Call Trace: >> > __dump_stack lib/dump_stack.c:17 [inline] >> > dump_stack+0x194/0x257 lib/dump_stack.c:53 >> > print_address_description+0x73/0x250 mm/kasan/report.c:252 >> > kasan_report_error mm/kasan/report.c:351 [inline] >> > kasan_report+0x25b/0x340 mm/kasan/report.c:409 >> > __asan_report_load1_noabort+0x14/0x20 mm/kasan/report.c:427 >> > strcmp+0x96/0xb0 lib/string.c:328 >> >> This seems to be out of bound read for "scontext" at >> >> for (i = 1; i < SECINITSID_NUM; i++) { >> if (!strcmp(initial_sid_to_string[i], scontext)) { >> *sid = i; >> return 0; >> } >> } >> >> because "initial_sid_to_string[i]" is "const char *". >> >> > security_context_to_sid_core+0x437/0x620 >> > security/selinux/ss/services.c:1420 >> > security_context_to_sid+0x32/0x40 >> > security/selinux/ss/services.c:1479 >> > selinux_setprocattr+0x51c/0xb50 security/selinux/hooks.c:5986 >> > security_setprocattr+0x85/0xc0 security/security.c:1264 >> >> If "value" does not terminate with '\0' or '\n', "value" and >> "size" are as-is passed to "scontext" and "scontext_len" above >> >> /* Obtain a SID for the context, if one was specified. */ >> if (size && str[0] && str[0] != '\n') { >> if (str[size-1] == '\n') { >> str[size-1] = 0; >> size--; >> } >> error = security_context_to_sid(value, size, &sid, >> GFP_KERNEL); >> >> which will allow strcmp() to trigger out of bound read when "size" is >> larger than strlen(initial_sid_to_string[i]). >> >> Thus, I guess the simplest fix is to use strncmp() instead of >> strcmp(). > > Already fixed by > https://www.spinics.net/lists/selinux/msg23589.html Paul, please also follow this part: > syzbot will keep track of this bug report. > Once a fix for this bug is committed, please reply to this email with: > #syz fix: exact-commit-title > Note: all commands must start from beginning of the line in the email body. This will greatly help to keep overall process running. Thanks.