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Message-ID: <20161116163021.tblhptv37r6byjvp@alphalink.fr>
Date: Wed, 16 Nov 2016 17:30:21 +0100
From: Guillaume Nault <g.nault@...halink.fr>
To: Baozeng Ding <sploving1@...il.com>
Cc: Cong Wang <xiyou.wangcong@...il.com>,
Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: net/l2tp:BUG: KASAN: use-after-free in l2tp_ip6_close
On Wed, Oct 19, 2016 at 10:52:03PM +0800, Baozeng Ding wrote:
> This use-after-free seems to be triggered by some race. I use stress tool for this:
> https://github.com/golang/tools/blob/master/cmd/stress/stress.go
> If you have Go toolchain installed, then the following will do:
> $ go get golang.org/x/tools/cmd/stress
> $ stress ./a.out
>
> =========================================================================
> #include <unistd.h>
> #include <stdint.h>
> #include <pthread.h>
> #include <stdio.h>
> #include <sys/socket.h>
> #include <linux/l2tp.h>
>
> int fd;
> struct sockaddr_l2tpip sock_addr = {
> .l2tp_family = AF_INET,
> .l2tp_unused = 0,
> .l2tp_addr = 0,
> .l2tp_conn_id = 8,
> .__pad = 0
>
> };
>
> void *thr(void *arg)
> {
> switch ((long)arg) {
> case 0:
> fd = socket(AF_INET, SOCK_DGRAM, IPPROTO_L2TP);
> break;
> case 1:
> bind(fd, (struct sockaddr*) &sock_addr, 0x10ul);
> break;
> case 2:
> bind(fd, (struct sockaddr*)&sock_addr, 0x10ul);
> break;
> case 3:
> connect(fd, (struct sockaddr*)&sock_addr, 0x10ul);
> break;
> }
> return 0;
> }
>
> int main()
> {
> long i;
> pthread_t th[4];
> int n;
> for (i = 0; i < 4; i++) {
> pthread_create(&th[i], 0, thr, (void*)i);
> usleep(10000);
> }
> for (i = 0; i < 4; i++) {
> pthread_create(&th[i], 0, thr, (void*)i);
> if (i%2==0)
> usleep(10000);
> }
> usleep(100000);
> return 0;
> }
>
This program targets l2tp_ip while the call trace is about l2tp_ip6. But it
looks like we have the same issue in both modules anyway.
> On 2016/10/17 3:50, Cong Wang wrote:
> > On Sun, Oct 16, 2016 at 8:07 AM, Baozeng Ding <sploving1@...il.com> wrote:
> >> Hello,
> >> While running syzkaller fuzzer I have got the following use-after-free
> >> bug in l2tp_ip6_close. The kernel version is 4.8.0+ (on Oct 7 commit d1f5323370fceaed43a7ee38f4c7bfc7e70f28d0).
> >>
> >> BUG: KASAN: use-after-free in l2tp_ip6_close+0x22e/0x290 at addr ffff8800081b0ed8
> >> Write of size 8 by task syz-executor/10987
> >> CPU: 0 PID: 10987 Comm: syz-executor Not tainted 4.8.0+ #39
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
> >> ffff880031d97838 ffffffff829f835b ffff88001b5a1640 ffff8800081b0ec0
> >> ffff8800081b15a0 ffff8800081b6d20 ffff880031d97860 ffffffff8174d3cc
> >> ffff880031d978f0 ffff8800081b0e80 ffff88001b5a1640 ffff880031d978e0
> >> Call Trace:
> >> [<ffffffff829f835b>] dump_stack+0xb3/0x118 lib/dump_stack.c:15
> >> [<ffffffff8174d3cc>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:156
> >> [< inline >] print_address_description mm/kasan/report.c:194
> >> [<ffffffff8174d666>] kasan_report_error+0x1f6/0x4d0 mm/kasan/report.c:283
> >> [< inline >] kasan_report mm/kasan/report.c:303
> >> [<ffffffff8174db7e>] __asan_report_store8_noabort+0x3e/0x40 mm/kasan/report.c:329
> >> [< inline >] __write_once_size ./include/linux/compiler.h:249
> >> [< inline >] __hlist_del ./include/linux/list.h:622
> >> [< inline >] hlist_del_init ./include/linux/list.h:637
> >> [<ffffffff8579047e>] l2tp_ip6_close+0x22e/0x290 net/l2tp/l2tp_ip6.c:239
> >
> >
> > This one looks pretty interesting, how the hell could we call ____fput() twice
> > on the same fd...
> >
> >
> >> [<ffffffff850b2dfd>] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:415
> >> [<ffffffff851dc5a0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422
> >> [<ffffffff84c4581d>] sock_release+0x8d/0x1d0 net/socket.c:570
> >> [<ffffffff84c45976>] sock_close+0x16/0x20 net/socket.c:1017
> >> [<ffffffff817a108c>] __fput+0x28c/0x780 fs/file_table.c:208
> >> [<ffffffff817a1605>] ____fput+0x15/0x20 fs/file_table.c:244
> >> [<ffffffff813774f9>] task_work_run+0xf9/0x170
> >> [<ffffffff81324aae>] do_exit+0x85e/0x2a00
> >> [<ffffffff81326dc8>] do_group_exit+0x108/0x330
> >> [<ffffffff81348cf7>] get_signal+0x617/0x17a0 kernel/signal.c:2307
> >> [<ffffffff811b49af>] do_signal+0x7f/0x18f0
> >> [<ffffffff810039bf>] exit_to_usermode_loop+0xbf/0x150 arch/x86/entry/common.c:156
> >> [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:190
> >> [<ffffffff81006060>] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259
> >> [<ffffffff85e4d726>] entry_SYSCALL_64_fastpath+0xc4/0xc6
> >> Object at ffff8800081b0ec0, in cache L2TP/IPv6 size: 1448
> >> Allocated:
> >> PID = 10987
> >> [ 1116.897025] [<ffffffff811ddcb6>] save_stack_trace+0x16/0x20
> >> [ 1116.897025] [<ffffffff8174c736>] save_stack+0x46/0xd0
> >> [ 1116.897025] [<ffffffff8174c9ad>] kasan_kmalloc+0xad/0xe0
> >> [ 1116.897025] [<ffffffff8174cee2>] kasan_slab_alloc+0x12/0x20
> >> [ 1116.897025] [< inline >] slab_post_alloc_hook mm/slab.h:417
> >> [ 1116.897025] [< inline >] slab_alloc_node mm/slub.c:2708
> >> [ 1116.897025] [< inline >] slab_alloc mm/slub.c:2716
> >> [ 1116.897025] [<ffffffff817476a8>] kmem_cache_alloc+0xc8/0x2b0 mm/slub.c:2721
> >> [ 1116.897025] [<ffffffff84c4f6a9>] sk_prot_alloc+0x69/0x2b0 net/core/sock.c:1326
> >> [ 1116.897025] [<ffffffff84c58ac8>] sk_alloc+0x38/0xae0 net/core/sock.c:1388
> >> [ 1116.897025] [<ffffffff851ddf67>] inet6_create+0x2d7/0x1000 net/ipv6/af_inet6.c:182
> >> [ 1116.897025] [<ffffffff84c4af7b>] __sock_create+0x37b/0x640 net/socket.c:1153
> >> [ 1116.897025] [< inline >] sock_create net/socket.c:1193
> >> [ 1116.897025] [< inline >] SYSC_socket net/socket.c:1223
> >> [ 1116.897025] [<ffffffff84c4b46f>] SyS_socket+0xef/0x1b0 net/socket.c:1203
> >> [ 1116.897025] [<ffffffff85e4d685>] entry_SYSCALL_64_fastpath+0x23/0xc6
> >> Freed:
> >> PID = 10987
> >> [ 1116.897025] [<ffffffff811ddcb6>] save_stack_trace+0x16/0x20
> >> [ 1116.897025] [<ffffffff8174c736>] save_stack+0x46/0xd0
> >> [ 1116.897025] [<ffffffff8174cf61>] kasan_slab_free+0x71/0xb0
> >> [ 1116.897025] [< inline >] slab_free_hook mm/slub.c:1352
> >> [ 1116.897025] [< inline >] slab_free_freelist_hook mm/slub.c:1374
> >> [ 1116.897025] [< inline >] slab_free mm/slub.c:2951
> >> [ 1116.897025] [<ffffffff81748b28>] kmem_cache_free+0xc8/0x330 mm/slub.c:2973
> >> [ 1116.897025] [< inline >] sk_prot_free net/core/sock.c:1369
> >> [ 1116.897025] [<ffffffff84c541eb>] __sk_destruct+0x32b/0x4f0 net/core/sock.c:1444
> >> [ 1116.897025] [<ffffffff84c5aca4>] sk_destruct+0x44/0x80 net/core/sock.c:1452
> >> [ 1116.897025] [<ffffffff84c5ad33>] __sk_free+0x53/0x220 net/core/sock.c:1460
> >> [ 1116.897025] [<ffffffff84c5af23>] sk_free+0x23/0x30 net/core/sock.c:1471
> >> [ 1116.897025] [<ffffffff84c5cb6c>] sk_common_release+0x28c/0x3e0 ./include/net/sock.h:1589
> >> [ 1116.897025] [<ffffffff8579044e>] l2tp_ip6_close+0x1fe/0x290 net/l2tp/l2tp_ip6.c:243
> >> [ 1116.897025] [<ffffffff850b2dfd>] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:415
> >> [ 1116.897025] [<ffffffff851dc5a0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422
> >> [ 1116.897025] [<ffffffff84c4581d>] sock_release+0x8d/0x1d0 net/socket.c:570
> >> [ 1116.897025] [<ffffffff84c45976>] sock_close+0x16/0x20 net/socket.c:1017
> >> [ 1116.897025] [<ffffffff817a108c>] __fput+0x28c/0x780 fs/file_table.c:208
> >> [ 1116.897025] [<ffffffff817a1605>] ____fput+0x15/0x20 fs/file_table.c:244
> >> [ 1116.897025] [<ffffffff813774f9>] task_work_run+0xf9/0x170
> >> [ 1116.897025] [<ffffffff81324aae>] do_exit+0x85e/0x2a00
> >> [ 1116.897025] [<ffffffff81326dc8>] do_group_exit+0x108/0x330
> >> [ 1116.897025] [<ffffffff81348cf7>] get_signal+0x617/0x17a0 kernel/signal.c:2307
> >> [ 1116.897025] [<ffffffff811b49af>] do_signal+0x7f/0x18f0
> >> [ 1116.897025] [<ffffffff810039bf>] exit_to_usermode_loop+0xbf/0x150 arch/x86/entry/common.c:156
> >> [ 1116.897025] [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:190
> >> [ 1116.897025] [<ffffffff81006060>] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259
> >> [ 1116.897025] [<ffffffff85e4d726>] entry_SYSCALL_64_fastpath+0xc4/0xc6
> >> Memory state around the buggy address:
> >> ffff8800081b0d80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >> ffff8800081b0e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >>> ffff8800081b0e80: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> >> ^
> >> ffff8800081b0f00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >> ffff8800081b0f80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >> ==================================================================
> >>
This looks very much like the one reported by Andrey a few days ago:
https://marc.info/?l=linux-netdev&m=147855869227527&w=2
The following patch should fix both l2tp_ip and l2tp_ip6:
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index fce25af..982f6c4 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -251,8 +251,6 @@ static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
int ret;
int chk_addr_ret;
- if (!sock_flag(sk, SOCK_ZAPPED))
- return -EINVAL;
if (addr_len < sizeof(struct sockaddr_l2tpip))
return -EINVAL;
if (addr->l2tp_family != AF_INET)
@@ -267,6 +265,9 @@ static int l2tp_ip_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
read_unlock_bh(&l2tp_ip_lock);
lock_sock(sk);
+ if (!sock_flag(sk, SOCK_ZAPPED))
+ goto out;
+
if (sk->sk_state != TCP_CLOSE || addr_len < sizeof(struct sockaddr_l2tpip))
goto out;
diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index ad3468c..9978d01 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -269,8 +269,6 @@ static int l2tp_ip6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
int addr_type;
int err;
- if (!sock_flag(sk, SOCK_ZAPPED))
- return -EINVAL;
if (addr->l2tp_family != AF_INET6)
return -EINVAL;
if (addr_len < sizeof(*addr))
@@ -296,6 +294,9 @@ static int l2tp_ip6_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len)
lock_sock(sk);
err = -EINVAL;
+ if (!sock_flag(sk, SOCK_ZAPPED))
+ goto out_unlock;
+
if (sk->sk_state != TCP_CLOSE)
goto out_unlock;
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