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 CE81F17723 for ; Thu, 20 Jul 2023 14:39:53 +0000 (UTC) Received: from mail-pg1-x532.google.com (mail-pg1-x532.google.com [IPv6:2607:f8b0:4864:20::532]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF04910FC for ; Thu, 20 Jul 2023 07:39:50 -0700 (PDT) Received: by mail-pg1-x532.google.com with SMTP id 41be03b00d2f7-54290603887so450384a12.1 for ; Thu, 20 Jul 2023 07:39:50 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; t=1689863990; x=1690468790; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=v70j74SNN6clF4fKRQ8qeEGthR3IYR+KXBl2pFd5Ol0=; b=TJZlEZzpGYz/DZ4/wPynNqyBo86TApSLBZnm/FHB5ycsF5NNdHA3qoyYTCn3izuLlf SGQBUx0/KdiYApSVXDPnTAh7IafW7yyNGmsGZ9fl0TtdKY1unl139uU7/SgT9wwmnwc7 4v4EakF2fbxg5+cDhYU9xLPYZGWdnxd6yU/H8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689863990; x=1690468790; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=v70j74SNN6clF4fKRQ8qeEGthR3IYR+KXBl2pFd5Ol0=; b=Bh05YvmiwjVRlj+1CiGjPJdBpyWiKmmksfTIosHOvXS1huKT3EQ2jm1g4BAyVbbw6c kkj1V8+0DNNHSTpMzIDE1cxxtydh4EPU/M7vSz+45XxLqqvlG4ruy+ytE0/MPtj3HZ4C h6RE2dDVQVRuYjD0DC6/5XAHCz2gxGuzzVhaiJrsUeF53egKjMkJyySIBc2S0CFmYebC VZcbnMri1O0GkcptHRajsNaFfNK65LZ2UR0Q/K9OHfrDPnX7/3Tw+QR3lX41tPaREd/L dZYM1MsCtnDuIMcmCyQoigwElAD12CQAACEU05IQmRdtixNEnG8c3UalTyJZSp4PJAgO DSEQ== X-Gm-Message-State: ABy/qLbt8a4B5Fl5jyn41rq+eA/XjTXJzlfiDPCndkv3oNKNQuVjS0P9 wSu1+6pqee0rArFE5AkIkvUQhA== X-Google-Smtp-Source: APBJJlEsFPLOmquoVflCipzXDkkPXHs8xB37uQgz6nXSQFrFOYBgjcw9m1jvGtgmOa1sEJsQMWHDBQ== X-Received: by 2002:a17:90a:4109:b0:262:cb1c:a782 with SMTP id u9-20020a17090a410900b00262cb1ca782mr17479495pjf.37.1689863990316; Thu, 20 Jul 2023 07:39:50 -0700 (PDT) Received: from www.outflux.net (198-0-35-241-static.hfc.comcastbusiness.net. [198.0.35.241]) by smtp.gmail.com with ESMTPSA id 13-20020a17090a030d00b0025bbe90d3cbsm1146168pje.44.2023.07.20.07.39.49 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Jul 2023 07:39:49 -0700 (PDT) Date: Thu, 20 Jul 2023 07:39:48 -0700 From: Kees Cook To: Kuniyuki Iwashima Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Willem de Bruijn , "Gustavo A. R. Silva" , Breno Leitao , Kuniyuki Iwashima , netdev@vger.kernel.org, syzkaller , Willem de Bruijn Subject: Re: [PATCH v2 net 1/2] af_unix: Fix fortify_panic() in unix_bind_bsd(). Message-ID: <202307200726.DBC8EAD9D@keescook> References: <20230720004410.87588-1-kuniyu@amazon.com> <20230720004410.87588-2-kuniyu@amazon.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230720004410.87588-2-kuniyu@amazon.com> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, RCVD_IN_DNSWL_BLOCKED,SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net 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 ...) 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. > 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