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 <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 > >> ================================================================== > >> 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;
