From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bn3nam01on0128.outbound.protection.outlook.com ([104.47.33.128]:55858 "EHLO NAM01-BN3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753523AbeA1W1s (ORCPT ); Sun, 28 Jan 2018 17:27:48 -0500 From: Sasha Levin To: "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" CC: Jann Horn , Pablo Neira Ayuso , Sasha Levin Subject: [PATCH AUTOSEL for 4.14 079/100] netfilter: xt_bpf: add overflow checks Date: Sun, 28 Jan 2018 22:26:50 +0000 Message-ID: <20180128222547.7398-79-alexander.levin@microsoft.com> References: <20180128222547.7398-1-alexander.levin@microsoft.com> In-Reply-To: <20180128222547.7398-1-alexander.levin@microsoft.com> Content-Language: en-US Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: stable-owner@vger.kernel.org List-ID: From: Jann Horn [ Upstream commit 6ab405114b0b229151ef06f4e31c7834dd09d0c0 ] Check whether inputs from userspace are too long (explicit length field too big or string not null-terminated) to avoid out-of-bounds reads. As far as I can tell, this can at worst lead to very limited kernel heap memory disclosure or oopses. This bug can be triggered by an unprivileged user even if the xt_bpf module is not loaded: iptables is available in network namespaces, and the xt_bpf module can be autoloaded. Triggering the bug with a classic BPF filter with fake length 0x1000 causes the following KASAN report: =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D BUG: KASAN: slab-out-of-bounds in bpf_prog_create+0x84/0xf0 Read of size 32768 at addr ffff8801eff2c494 by task test/4627 CPU: 0 PID: 4627 Comm: test Not tainted 4.15.0-rc1+ #1 [...] Call Trace: dump_stack+0x5c/0x85 print_address_description+0x6a/0x260 kasan_report+0x254/0x370 ? bpf_prog_create+0x84/0xf0 memcpy+0x1f/0x50 bpf_prog_create+0x84/0xf0 bpf_mt_check+0x90/0xd6 [xt_bpf] [...] Allocated by task 4627: kasan_kmalloc+0xa0/0xd0 __kmalloc_node+0x47/0x60 xt_alloc_table_info+0x41/0x70 [x_tables] [...] The buggy address belongs to the object at ffff8801eff2c3c0 which belongs to the cache kmalloc-2048 of size 2048 The buggy address is located 212 bytes inside of 2048-byte region [ffff8801eff2c3c0, ffff8801eff2cbc0) [...] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Fixes: e6f30c731718 ("netfilter: x_tables: add xt_bpf match") Signed-off-by: Jann Horn Signed-off-by: Pablo Neira Ayuso Signed-off-by: Sasha Levin --- net/netfilter/xt_bpf.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/netfilter/xt_bpf.c b/net/netfilter/xt_bpf.c index 29123934887b..5185ff0f8f58 100644 --- a/net/netfilter/xt_bpf.c +++ b/net/netfilter/xt_bpf.c @@ -27,6 +27,9 @@ static int __bpf_mt_check_bytecode(struct sock_filter *in= sns, __u16 len, { struct sock_fprog_kern program; =20 + if (len > XT_BPF_MAX_NUM_INSTR) + return -EINVAL; + program.len =3D len; program.filter =3D insns; =20 @@ -55,6 +58,9 @@ static int __bpf_mt_check_path(const char *path, struct b= pf_prog **ret) mm_segment_t oldfs =3D get_fs(); int retval, fd; =20 + if (strnlen(path, XT_BPF_PATH_MAX) =3D=3D XT_BPF_PATH_MAX) + return -EINVAL; + set_fs(KERNEL_DS); fd =3D bpf_obj_get_user(path); set_fs(oldfs); --=20 2.11.0