From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 130D32FA28 for ; Thu, 20 Jul 2023 17:09:46 +0000 (UTC) Received: from smtp-fw-52004.amazon.com (smtp-fw-52004.amazon.com [52.119.213.154]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 14E8C1995 for ; Thu, 20 Jul 2023 10:09:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1689872984; x=1721408984; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=+uq2OtB8q9syx6TUPSFkYRlI9ZR8D9FvAPqVL5EwPMA=; b=rEQbXf/aOXNuetRoMA3apZ48uFUIrFW1Tr+OvrzDNzv3sUMwDF7jRaBG gOaLmbB9q+WdH84AsZkWObr6nIJL11luLlho7yeWBUqsTfkJ+hUYYSsyM hN6q25ivDxKLjbYsgvAkSI8WPYLv8T83rJZGDWlrKnzv0w45049OHL92R M=; X-IronPort-AV: E=Sophos;i="6.01,219,1684800000"; d="scan'208";a="143836634" Received: from iad12-co-svc-p1-lb1-vlan2.amazon.com (HELO email-inbound-relay-iad-1e-m6i4x-a65ebc6e.us-east-1.amazon.com) ([10.43.8.2]) by smtp-border-fw-52004.iad7.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Jul 2023 17:09:41 +0000 Received: from EX19MTAUWB002.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1e-m6i4x-a65ebc6e.us-east-1.amazon.com (Postfix) with ESMTPS id 6C7B9667A0; Thu, 20 Jul 2023 17:09:37 +0000 (UTC) Received: from EX19D004ANA001.ant.amazon.com (10.37.240.138) by EX19MTAUWB002.ant.amazon.com (10.250.64.231) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.30; Thu, 20 Jul 2023 17:09:36 +0000 Received: from 88665a182662.ant.amazon.com (10.106.101.12) by EX19D004ANA001.ant.amazon.com (10.37.240.138) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.30; Thu, 20 Jul 2023 17:09:33 +0000 From: Kuniyuki Iwashima To: CC: , , , , , , , , , , , Subject: Re: [PATCH v2 net 1/2] af_unix: Fix fortify_panic() in unix_bind_bsd(). Date: Thu, 20 Jul 2023 10:09:25 -0700 Message-ID: <20230720170925.4798-1-kuniyu@amazon.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <202307200726.DBC8EAD9D@keescook> References: <202307200726.DBC8EAD9D@keescook> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.106.101.12] X-ClientProxiedBy: EX19D032UWB004.ant.amazon.com (10.13.139.136) To EX19D004ANA001.ant.amazon.com (10.37.240.138) Precedence: Bulk X-Spam-Status: No, score=-4.0 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H5,RCVD_IN_MSPIKE_WL,SPF_HELO_NONE, T_SCC_BODY_TEXT_LINE,T_SPF_PERMERROR autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net From: Kees Cook Date: Thu, 20 Jul 2023 07:39:48 -0700 > On Wed, Jul 19, 2023 at 05:44:09PM -0700, Kuniyuki Iwashima wrote: > > syzkaller found a bug in unix_bind_bsd() [0]. We can reproduce it > > by bind()ing a socket on a path with length 108. > > > > 108 is the size of sun_addr of struct sockaddr_un and is the maximum > > valid length for the pathname socket. When calling bind(), we use > > struct sockaddr_storage as the actual buffer size, so terminating > > sun_addr[108] with null is legitimate. > > > > However, strlen(sunaddr) for such a case causes fortify_panic() if > > CONFIG_FORTIFY_SOURCE=y. __fortify_strlen() has no idea about the > > actual buffer size and takes 108 as overflow, although 108 still > > fits in struct sockaddr_storage. > > Oh, the max size is 108, but it's allowed to be unterminated? This seems > to contradict the comment for unix_validate_addr() (which then doesn't > validate this ...) Because we call it for the abstract socket too which starts with \0 and does not handle it specially. > Reading "max 7 unix" seems to clear this up and > confirm that it doesn't need to be terminated. Bleh. > > Regardless, see below for a simpler solution, since this doesn't need to > be arbitrarily long, just potentially unterminated. unix_mkname_bsd() terminates it. Technically, we need not call strlen() if we don't optimise the allocated string length. connect() does not need strlen() and just calls unix_mkname_bsd() in unix_find_bsd(). > > > Let's make __fortify_strlen() recognise the actual buffer size. > > > > [0]: > > detected buffer overflow in __fortify_strlen > > kernel BUG at lib/string_helpers.c:1031! > > Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP > > Modules linked in: > > CPU: 0 PID: 255 Comm: syz-executor296 Not tainted 6.5.0-rc1-00330-g60cc1f7d0605 #4 > > Hardware name: linux,dummy-virt (DT) > > pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > > pc : fortify_panic+0x1c/0x20 lib/string_helpers.c:1030 > > lr : fortify_panic+0x1c/0x20 lib/string_helpers.c:1030 > > sp : ffff800089817af0 > > x29: ffff800089817af0 x28: ffff800089817b40 x27: 1ffff00011302f68 > > x26: 000000000000006e x25: 0000000000000012 x24: ffff800087e60140 > > x23: dfff800000000000 x22: ffff800089817c20 x21: ffff800089817c8e > > x20: 000000000000006c x19: ffff00000c323900 x18: ffff800086ab1630 > > x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000001 > > x14: 1ffff00011302eb8 x13: 0000000000000000 x12: 0000000000000000 > > x11: 0000000000000000 x10: 0000000000000000 x9 : 64a26b65474d2a00 > > x8 : 64a26b65474d2a00 x7 : 0000000000000001 x6 : 0000000000000001 > > x5 : ffff800089817438 x4 : ffff800086ac99e0 x3 : ffff800080f19e8c > > x2 : 0000000000000001 x1 : 0000000100000000 x0 : 000000000000002c > > Call trace: > > fortify_panic+0x1c/0x20 lib/string_helpers.c:1030 > > _Z16__fortify_strlenPKcU25pass_dynamic_object_size1 include/linux/fortify-string.h:217 [inline] > > unix_bind_bsd net/unix/af_unix.c:1212 [inline] > > unix_bind+0xba8/0xc58 net/unix/af_unix.c:1326 > > __sys_bind+0x1ac/0x248 net/socket.c:1792 > > __do_sys_bind net/socket.c:1803 [inline] > > __se_sys_bind net/socket.c:1801 [inline] > > __arm64_sys_bind+0x7c/0x94 net/socket.c:1801 > > __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline] > > invoke_syscall+0x98/0x2c0 arch/arm64/kernel/syscall.c:52 > > el0_svc_common+0x134/0x240 arch/arm64/kernel/syscall.c:139 > > do_el0_svc+0x64/0x198 arch/arm64/kernel/syscall.c:188 > > el0_svc+0x2c/0x7c arch/arm64/kernel/entry-common.c:647 > > el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:665 > > el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:591 > > Code: aa0003e1 d0000e80 91030000 97ffc91a (d4210000) > > > > Fixes: df8fc4e934c1 ("kbuild: Enable -fstrict-flex-arrays=3") > > Reported-by: syzkaller > > Signed-off-by: Kuniyuki Iwashima > > Reviewed-by: Willem de Bruijn > > --- > > net/unix/af_unix.c | 16 +++++++++++++--- > > 1 file changed, 13 insertions(+), 3 deletions(-) > > > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c > > index 123b35ddfd71..e1b1819b96d1 100644 > > --- a/net/unix/af_unix.c > > +++ b/net/unix/af_unix.c > > @@ -302,6 +302,18 @@ static void unix_mkname_bsd(struct sockaddr_un *sunaddr, int addr_len) > > ((char *)sunaddr)[addr_len] = 0; > > } > > > > +static int unix_strlen_bsd(struct sockaddr_un *sunaddr) > > +{ > > + /* Don't pass sunaddr->sun_path to strlen(). Otherwise, the > > + * max valid length UNIX_PATH_MAX (108) will cause panic if > > + * CONFIG_FORTIFY_SOURCE=y. Let __fortify_strlen() know that > > + * the actual buffer is struct sockaddr_storage and that 108 > > + * is within __data[]. See also: unix_mkname_bsd(). > > + */ > > + return strlen(((struct sockaddr_storage *)sunaddr)->__data) + > > + offsetof(struct sockaddr_un, sun_path) + 1; > > +} > > + > > static void __unix_remove_socket(struct sock *sk) > > { > > sk_del_node_init(sk); > > @@ -1209,9 +1221,7 @@ static int unix_bind_bsd(struct sock *sk, struct sockaddr_un *sunaddr, > > int err; > > > > unix_mkname_bsd(sunaddr, addr_len); > > - addr_len = strlen(sunaddr->sun_path) + > > Instead of a whole new function, I think this can just be: > > strnlen(sunaddr->sun_path, sizeof(sunaddr->sun_path)) + > > > - offsetof(struct sockaddr_un, sun_path) + 1; > > - > > + addr_len = unix_strlen_bsd(sunaddr); > > addr = unix_create_addr(sunaddr, addr_len); > > if (!addr) > > return -ENOMEM; > > -- > > 2.30.2 > > > > -- > Kees Cook