From 32c231164b762dddefa13af5a0101032c70b50ef Mon Sep 17 00:00:00 2001 From: Guillaume Nault Date: Fri, 18 Nov 2016 22:13:00 +0100 Subject: [PATCH] l2tp: fix racy SOCK_ZAPPED flag check in l2tp_ip{,6}_bind() Lock socket before checking the SOCK_ZAPPED flag in l2tp_ip6_bind(). Without lock, a concurrent call could modify the socket flags between the sock_flag(sk, SOCK_ZAPPED) test and the lock_sock() call. This way, a socket could be inserted twice in l2tp_ip6_bind_table. Releasing it would then leave a stale pointer there, generating use-after-free errors when walking through the list or modifying adjacent entries. 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: [] dump_stack+0xb3/0x118 lib/dump_stack.c:15 [] kasan_object_err+0x1c/0x70 mm/kasan/report.c:156 [< inline >] print_address_description mm/kasan/report.c:194 [] kasan_report_error+0x1f6/0x4d0 mm/kasan/report.c:283 [< inline >] kasan_report mm/kasan/report.c:303 [] __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 [] l2tp_ip6_close+0x22e/0x290 net/l2tp/l2tp_ip6.c:239 [] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:415 [] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422 [] sock_release+0x8d/0x1d0 net/socket.c:570 [] sock_close+0x16/0x20 net/socket.c:1017 [] __fput+0x28c/0x780 fs/file_table.c:208 [] ____fput+0x15/0x20 fs/file_table.c:244 [] task_work_run+0xf9/0x170 [] do_exit+0x85e/0x2a00 [] do_group_exit+0x108/0x330 [] get_signal+0x617/0x17a0 kernel/signal.c:2307 [] do_signal+0x7f/0x18f0 [] exit_to_usermode_loop+0xbf/0x150 arch/x86/entry/common.c:156 [< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:190 [] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259 [] entry_SYSCALL_64_fastpath+0xc4/0xc6 Object at ffff8800081b0ec0, in cache L2TP/IPv6 size: 1448 Allocated: PID = 10987 [ 1116.897025] [] save_stack_trace+0x16/0x20 [ 1116.897025] [] save_stack+0x46/0xd0 [ 1116.897025] [] kasan_kmalloc+0xad/0xe0 [ 1116.897025] [] 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] [] kmem_cache_alloc+0xc8/0x2b0 mm/slub.c:2721 [ 1116.897025] [] sk_prot_alloc+0x69/0x2b0 net/core/sock.c:1326 [ 1116.897025] [] sk_alloc+0x38/0xae0 net/core/sock.c:1388 [ 1116.897025] [] inet6_create+0x2d7/0x1000 net/ipv6/af_inet6.c:182 [ 1116.897025] [] __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] [] SyS_socket+0xef/0x1b0 net/socket.c:1203 [ 1116.897025] [] entry_SYSCALL_64_fastpath+0x23/0xc6 Freed: PID = 10987 [ 1116.897025] [] save_stack_trace+0x16/0x20 [ 1116.897025] [] save_stack+0x46/0xd0 [ 1116.897025] [] 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] [] kmem_cache_free+0xc8/0x330 mm/slub.c:2973 [ 1116.897025] [< inline >] sk_prot_free net/core/sock.c:1369 [ 1116.897025] [] __sk_destruct+0x32b/0x4f0 net/core/sock.c:1444 [ 1116.897025] [] sk_destruct+0x44/0x80 net/core/sock.c:1452 [ 1116.897025] [] __sk_free+0x53/0x220 net/core/sock.c:1460 [ 1116.897025] [] sk_free+0x23/0x30 net/core/sock.c:1471 [ 1116.897025] [] sk_common_release+0x28c/0x3e0 ./include/net/sock.h:1589 [ 1116.897025] [] l2tp_ip6_close+0x1fe/0x290 net/l2tp/l2tp_ip6.c:243 [ 1116.897025] [] inet_release+0xed/0x1c0 net/ipv4/af_inet.c:415 [ 1116.897025] [] inet6_release+0x50/0x70 net/ipv6/af_inet6.c:422 [ 1116.897025] [] sock_release+0x8d/0x1d0 net/socket.c:570 [ 1116.897025] [] sock_close+0x16/0x20 net/socket.c:1017 [ 1116.897025] [] __fput+0x28c/0x780 fs/file_table.c:208 [ 1116.897025] [] ____fput+0x15/0x20 fs/file_table.c:244 [ 1116.897025] [] task_work_run+0xf9/0x170 [ 1116.897025] [] do_exit+0x85e/0x2a00 [ 1116.897025] [] do_group_exit+0x108/0x330 [ 1116.897025] [] get_signal+0x617/0x17a0 kernel/signal.c:2307 [ 1116.897025] [] do_signal+0x7f/0x18f0 [ 1116.897025] [] 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] [] syscall_return_slowpath+0x1a0/0x1e0 arch/x86/entry/common.c:259 [ 1116.897025] [] 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 ================================================================== The same issue exists with l2tp_ip_bind() and l2tp_ip_bind_table. Fixes: c51ce49735c1 ("l2tp: fix oops in L2TP IP sockets for connect() AF_UNSPEC case") Reported-by: Baozeng Ding Reported-by: Andrey Konovalov Tested-by: Baozeng Ding Signed-off-by: Guillaume Nault Signed-off-by: David S. Miller --- net/l2tp/l2tp_ip.c | 5 +++-- net/l2tp/l2tp_ip6.c | 5 +++-- 2 files changed, 6 insertions(+), 4 deletions(-) diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c index fce25afb652a..982f6c44ea01 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 ad3468c32b53..9978d01ba0ba 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; -- 2.20.1