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;
}
On 2016/10/17 3:50, Cong Wang wrote:
> On Sun, Oct 16, 2016 at 8:07 AM, Baozeng Ding <splovi...@gmail.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
>> ==================================================================
>>
>> Best Regards,
>> Baozeng Ding
