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;