Re: net/l2tp: use-after-free write in l2tp_ip6_close
From: Guillaume Nault
Date: Thu Nov 10 2016 - 12:50:09 EST
On Mon, Nov 07, 2016 at 11:35:26PM +0100, Andrey Konovalov wrote:
> Hi,
>
> I've got the following error report while running the syzkaller fuzzer:
>
> ==================================================================
> BUG: KASAN: use-after-free in l2tp_ip6_close+0x239/0x2a0 at addr
> ffff8800677276d8
> Write of size 8 by task a.out/8668
> CPU: 0 PID: 8668 Comm: a.out Not tainted 4.9.0-rc4+ #354
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> ffff8800694d7b00 ffffffff81b46a64 ffff88006adb5780 ffff8800677276c0
> ffff880067727c68 ffff8800677276c0 ffff8800694d7b28 ffffffff8150a86c
> ffff8800694d7bb8 ffff88006adb5780 ffff8800e77276d8 ffff8800694d7ba8
> Call Trace:
> [< inline >] __dump_stack lib/dump_stack.c:15
> [<ffffffff81b46a64>] dump_stack+0xb3/0x10f lib/dump_stack.c:51
> [<ffffffff8150a86c>] kasan_object_err+0x1c/0x70 mm/kasan/report.c:156
> [< inline >] print_address_description mm/kasan/report.c:194
> [<ffffffff8150ab07>] kasan_report_error+0x1f7/0x4d0 mm/kasan/report.c:283
> [< inline >] kasan_report mm/kasan/report.c:303
> [<ffffffff8150b01e>] __asan_report_store8_noabort+0x3e/0x40
> mm/kasan/report.c:329
> [< inline >] __write_once_size ./include/linux/compiler.h:272
> [< inline >] __hlist_del ./include/linux/list.h:622
> [< inline >] hlist_del_init ./include/linux/list.h:637
> [<ffffffff83825f49>] l2tp_ip6_close+0x239/0x2a0 net/l2tp/l2tp_ip6.c:239
> [<ffffffff8316b31f>] inet_release+0xef/0x1c0 net/ipv4/af_inet.c:415
> [<ffffffff832cd4d0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422
> [<ffffffff82b6d89e>] sock_release+0x8e/0x1d0 net/socket.c:570
> [<ffffffff82b6d9f6>] sock_close+0x16/0x20 net/socket.c:1017
> [<ffffffff81524bdd>] __fput+0x29d/0x720 fs/file_table.c:208
> [<ffffffff815250e5>] ____fput+0x15/0x20 fs/file_table.c:244
> [<ffffffff81172928>] task_work_run+0xf8/0x170 kernel/task_work.c:116
> [< inline >] exit_task_work ./include/linux/task_work.h:21
> [<ffffffff8111bda3>] do_exit+0x883/0x2ac0 kernel/exit.c:828
> [<ffffffff8112234e>] do_group_exit+0x10e/0x340 kernel/exit.c:931
> [< inline >] SYSC_exit_group kernel/exit.c:942
> [<ffffffff8112259d>] SyS_exit_group+0x1d/0x20 kernel/exit.c:940
> [<ffffffff83fc1501>] entry_SYSCALL_64_fastpath+0x1f/0xc2
> arch/x86/entry/entry_64.S:209
> Object at ffff8800677276c0, in cache L2TP/IPv6 size: 1448
> Allocated:
> PID = 8692
> [<ffffffff8107e236>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
> [<ffffffff81509bd6>] save_stack+0x46/0xd0 mm/kasan/kasan.c:495
> [< inline >] set_track mm/kasan/kasan.c:507
> [<ffffffff81509e4b>] kasan_kmalloc+0xab/0xe0 mm/kasan/kasan.c:598
> [<ffffffff8150a3b2>] kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:537
> [< inline >] slab_post_alloc_hook mm/slab.h:417
> [< inline >] slab_alloc_node mm/slub.c:2708
> [< inline >] slab_alloc mm/slub.c:2716
> [<ffffffff81505064>] kmem_cache_alloc+0xb4/0x270 mm/slub.c:2721
> [<ffffffff82b77ca9>] sk_prot_alloc+0x69/0x2b0 net/core/sock.c:1327
> [<ffffffff82b80898>] sk_alloc+0x38/0xaf0 net/core/sock.c:1389
> [<ffffffff832cef05>] inet6_create+0x2e5/0xf60 net/ipv6/af_inet6.c:182
> [<ffffffff82b7301f>] __sock_create+0x37f/0x640 net/socket.c:1153
> [< inline >] sock_create net/socket.c:1193
> [< inline >] SYSC_socket net/socket.c:1223
> [<ffffffff82b73510>] SyS_socket+0xf0/0x1b0 net/socket.c:1203
> [<ffffffff83fc1501>] entry_SYSCALL_64_fastpath+0x1f/0xc2
> arch/x86/entry/entry_64.S:209
> Freed:
> PID = 8668
> [<ffffffff8107e236>] save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
> [<ffffffff81509bd6>] save_stack+0x46/0xd0 mm/kasan/kasan.c:495
> [< inline >] set_track mm/kasan/kasan.c:507
> [<ffffffff8150a433>] kasan_slab_free+0x73/0xc0 mm/kasan/kasan.c:571
> [< inline >] slab_free_hook mm/slub.c:1352
> [< inline >] slab_free_freelist_hook mm/slub.c:1374
> [< inline >] slab_free mm/slub.c:2951
> [<ffffffff81506263>] kmem_cache_free+0xb3/0x2c0 mm/slub.c:2973
> [< inline >] sk_prot_free net/core/sock.c:1370
> [<ffffffff82b7c669>] __sk_destruct+0x319/0x480 net/core/sock.c:1445
> [<ffffffff82b82b94>] sk_destruct+0x44/0x80 net/core/sock.c:1453
> [<ffffffff82b82c24>] __sk_free+0x54/0x230 net/core/sock.c:1461
> [<ffffffff82b82e23>] sk_free+0x23/0x30 net/core/sock.c:1472
> [< inline >] sock_put ./include/net/sock.h:1591
> [<ffffffff82b84b04>] sk_common_release+0x294/0x3e0 net/core/sock.c:2745
> [<ffffffff83825f19>] l2tp_ip6_close+0x209/0x2a0 net/l2tp/l2tp_ip6.c:243
> [<ffffffff8316b31f>] inet_release+0xef/0x1c0 net/ipv4/af_inet.c:415
> [<ffffffff832cd4d0>] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422
> [<ffffffff82b6d89e>] sock_release+0x8e/0x1d0 net/socket.c:570
> [<ffffffff82b6d9f6>] sock_close+0x16/0x20 net/socket.c:1017
> [<ffffffff81524bdd>] __fput+0x29d/0x720 fs/file_table.c:208
> [<ffffffff815250e5>] ____fput+0x15/0x20 fs/file_table.c:244
> [<ffffffff81172928>] task_work_run+0xf8/0x170 kernel/task_work.c:116
> [< inline >] exit_task_work ./include/linux/task_work.h:21
> [<ffffffff8111bda3>] do_exit+0x883/0x2ac0 kernel/exit.c:828
> [<ffffffff8112234e>] do_group_exit+0x10e/0x340 kernel/exit.c:931
> [< inline >] SYSC_exit_group kernel/exit.c:942
> [<ffffffff8112259d>] SyS_exit_group+0x1d/0x20 kernel/exit.c:940
> [<ffffffff83fc1501>] entry_SYSCALL_64_fastpath+0x1f/0xc2
> arch/x86/entry/entry_64.S:209
> Memory state around the buggy address:
> ffff880067727580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff880067727600: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc
> >ffff880067727680: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
> ^
> ffff880067727700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff880067727780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
> To reproduce run the attached program in a tight parallel loop using
> stress (https://godoc.org/golang.org/x/tools/cmd/stress):
> $ gcc -lpthread tmp.c
> $ ./stress ./a.out
>
> On commit bc33b0ca11e3df467777a4fa7639ba488c9d4911 (Nov 5).
>
Thanks for the report. It looks like l2tp_ip6_bind() is racy.
Can you try the following patch?
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;