gtp: Fix use-after-free in __gtp_encap_destroy().

syzkaller reported use-after-free in __gtp_encap_destroy(). [0]

It shows the same process freed sk and touched it illegally.

Commit e198987e7d ("gtp: fix suspicious RCU usage") added lock_sock()
and release_sock() in __gtp_encap_destroy() to protect sk->sk_user_data,
but release_sock() is called after sock_put() releases the last refcnt.

[0]:
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: slab-use-after-free in atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:541 [inline]
BUG: KASAN: slab-use-after-free in queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
BUG: KASAN: slab-use-after-free in do_raw_spin_lock include/linux/spinlock.h:186 [inline]
BUG: KASAN: slab-use-after-free in __raw_spin_lock_bh include/linux/spinlock_api_smp.h:127 [inline]
BUG: KASAN: slab-use-after-free in _raw_spin_lock_bh+0x75/0xe0 kernel/locking/spinlock.c:178
Write of size 4 at addr ffff88800dbef398 by task syz-executor.2/2401

CPU: 1 PID: 2401 Comm: syz-executor.2 Not tainted 6.4.0-rc5-01219-gfa0e21fa4443 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x72/0xa0 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:351 [inline]
 print_report+0xcc/0x620 mm/kasan/report.c:462
 kasan_report+0xb2/0xe0 mm/kasan/report.c:572
 check_region_inline mm/kasan/generic.c:181 [inline]
 kasan_check_range+0x39/0x1c0 mm/kasan/generic.c:187
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:541 [inline]
 queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
 do_raw_spin_lock include/linux/spinlock.h:186 [inline]
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:127 [inline]
 _raw_spin_lock_bh+0x75/0xe0 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:355 [inline]
 release_sock+0x1f/0x1a0 net/core/sock.c:3526
 gtp_encap_disable_sock drivers/net/gtp.c:651 [inline]
 gtp_encap_disable+0xb9/0x220 drivers/net/gtp.c:664
 gtp_dev_uninit+0x19/0x50 drivers/net/gtp.c:728
 unregister_netdevice_many_notify+0x97e/0x1520 net/core/dev.c:10841
 rtnl_delete_link net/core/rtnetlink.c:3216 [inline]
 rtnl_dellink+0x3c0/0xb30 net/core/rtnetlink.c:3268
 rtnetlink_rcv_msg+0x450/0xb10 net/core/rtnetlink.c:6423
 netlink_rcv_skb+0x15d/0x450 net/netlink/af_netlink.c:2548
 netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
 netlink_unicast+0x700/0x930 net/netlink/af_netlink.c:1365
 netlink_sendmsg+0x91c/0xe30 net/netlink/af_netlink.c:1913
 sock_sendmsg_nosec net/socket.c:724 [inline]
 sock_sendmsg+0x1b7/0x200 net/socket.c:747
 ____sys_sendmsg+0x75a/0x990 net/socket.c:2493
 ___sys_sendmsg+0x11d/0x1c0 net/socket.c:2547
 __sys_sendmsg+0xfe/0x1d0 net/socket.c:2576
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3f/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc
RIP: 0033:0x7f1168b1fe5d
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 73 9f 1b 00 f7 d8 64 89 01 48
RSP: 002b:00007f1167edccc8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004bbf80 RCX: 00007f1168b1fe5d
RDX: 0000000000000000 RSI: 00000000200002c0 RDI: 0000000000000003
RBP: 00000000004bbf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f1168b80530 R15: 0000000000000000
 </TASK>

Allocated by task 1483:
 kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 __kasan_slab_alloc+0x59/0x70 mm/kasan/common.c:328
 kasan_slab_alloc include/linux/kasan.h:186 [inline]
 slab_post_alloc_hook mm/slab.h:711 [inline]
 slab_alloc_node mm/slub.c:3451 [inline]
 slab_alloc mm/slub.c:3459 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3466 [inline]
 kmem_cache_alloc+0x16d/0x340 mm/slub.c:3475
 sk_prot_alloc+0x5f/0x280 net/core/sock.c:2073
 sk_alloc+0x34/0x6c0 net/core/sock.c:2132
 inet6_create net/ipv6/af_inet6.c:192 [inline]
 inet6_create+0x2c7/0xf20 net/ipv6/af_inet6.c:119
 __sock_create+0x2a1/0x530 net/socket.c:1535
 sock_create net/socket.c:1586 [inline]
 __sys_socket_create net/socket.c:1623 [inline]
 __sys_socket_create net/socket.c:1608 [inline]
 __sys_socket+0x137/0x250 net/socket.c:1651
 __do_sys_socket net/socket.c:1664 [inline]
 __se_sys_socket net/socket.c:1662 [inline]
 __x64_sys_socket+0x72/0xb0 net/socket.c:1662
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3f/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Freed by task 2401:
 kasan_save_stack+0x22/0x50 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:521
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free mm/kasan/common.c:200 [inline]
 __kasan_slab_free+0x10c/0x1b0 mm/kasan/common.c:244
 kasan_slab_free include/linux/kasan.h:162 [inline]
 slab_free_hook mm/slub.c:1781 [inline]
 slab_free_freelist_hook mm/slub.c:1807 [inline]
 slab_free mm/slub.c:3786 [inline]
 kmem_cache_free+0xb4/0x490 mm/slub.c:3808
 sk_prot_free net/core/sock.c:2113 [inline]
 __sk_destruct+0x500/0x720 net/core/sock.c:2207
 sk_destruct+0xc1/0xe0 net/core/sock.c:2222
 __sk_free+0xed/0x3d0 net/core/sock.c:2233
 sk_free+0x7c/0xa0 net/core/sock.c:2244
 sock_put include/net/sock.h:1981 [inline]
 __gtp_encap_destroy+0x165/0x1b0 drivers/net/gtp.c:634
 gtp_encap_disable_sock drivers/net/gtp.c:651 [inline]
 gtp_encap_disable+0xb9/0x220 drivers/net/gtp.c:664
 gtp_dev_uninit+0x19/0x50 drivers/net/gtp.c:728
 unregister_netdevice_many_notify+0x97e/0x1520 net/core/dev.c:10841
 rtnl_delete_link net/core/rtnetlink.c:3216 [inline]
 rtnl_dellink+0x3c0/0xb30 net/core/rtnetlink.c:3268
 rtnetlink_rcv_msg+0x450/0xb10 net/core/rtnetlink.c:6423
 netlink_rcv_skb+0x15d/0x450 net/netlink/af_netlink.c:2548
 netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
 netlink_unicast+0x700/0x930 net/netlink/af_netlink.c:1365
 netlink_sendmsg+0x91c/0xe30 net/netlink/af_netlink.c:1913
 sock_sendmsg_nosec net/socket.c:724 [inline]
 sock_sendmsg+0x1b7/0x200 net/socket.c:747
 ____sys_sendmsg+0x75a/0x990 net/socket.c:2493
 ___sys_sendmsg+0x11d/0x1c0 net/socket.c:2547
 __sys_sendmsg+0xfe/0x1d0 net/socket.c:2576
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3f/0x90 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

The buggy address belongs to the object at ffff88800dbef300
 which belongs to the cache UDPv6 of size 1344
The buggy address is located 152 bytes inside of
 freed 1344-byte region [ffff88800dbef300, ffff88800dbef840)

The buggy address belongs to the physical page:
page:00000000d31bfed5 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88800dbeed40 pfn:0xdbe8
head:00000000d31bfed5 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888008ee0801
flags: 0x100000000010200(slab|head|node=0|zone=1)
page_type: 0xffffffff()
raw: 0100000000010200 ffff88800c7a3000 dead000000000122 0000000000000000
raw: ffff88800dbeed40 0000000080160015 00000001ffffffff ffff888008ee0801
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88800dbef280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88800dbef300: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88800dbef380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                            ^
 ffff88800dbef400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88800dbef480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb

Fixes: e198987e7d ("gtp: fix suspicious RCU usage")
Reported-by: syzkaller <syzkaller@googlegroups.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>
Link: https://lore.kernel.org/r/20230622213231.24651-1-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/gtp.c

@@ -631,7 +631,9 @@ static void __gtp_encap_destroy(struct sock *sk)
 			gtp->sk1u = NULL;
 		udp_sk(sk)->encap_type = 0;
 		rcu_assign_sk_user_data(sk, NULL);
+		release_sock(sk);
 		sock_put(sk);
+		return;
 	}
 	release_sock(sk);
 }