=============================
WARNING: suspicious RCU usage
4.15.0-rc1+ #203 Not tainted
-----------------------------
./include/trace/events/kmem.h:142 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syzkaller938817/3084:
 #0:  (sk_lock-AF_ALG){+.+.}, at: [<000000007fde27e4>] lock_sock include/net/sock.h:1465 [inline]
 #0:  (sk_lock-AF_ALG){+.+.}, at: [<000000007fde27e4>] af_alg_wait_for_data+0x2f2/0x650 crypto/af_alg.c:768

stack backtrace:
CPU: 0 PID: 3084 Comm: syzkaller938817 Not tainted 4.15.0-rc1+ #203
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4675
 trace_kfree include/trace/events/kmem.h:137 [inline]
 kfree+0x20a/0x250 mm/slab.c:3796
 blkcipher_walk_done+0x72b/0xde0 crypto/blkcipher.c:139
 encrypt+0x50a/0xaf0 crypto/salsa20_generic.c:208
 skcipher_crypt_blkcipher crypto/skcipher.c:622 [inline]
 skcipher_decrypt_blkcipher+0x213/0x310 crypto/skcipher.c:640
 crypto_skcipher_decrypt include/crypto/skcipher.h:463 [inline]
 _skcipher_recvmsg crypto/algif_skcipher.c:144 [inline]
 skcipher_recvmsg+0xa54/0xf20 crypto/algif_skcipher.c:165
 sock_recvmsg_nosec net/socket.c:805 [inline]
 sock_recvmsg+0xc9/0x110 net/socket.c:812
 ___sys_recvmsg+0x29b/0x630 net/socket.c:2207
 __sys_recvmsg+0xe2/0x210 net/socket.c:2252
 SYSC_recvmsg net/socket.c:2264 [inline]
 SyS_recvmsg+0x2d/0x50 net/socket.c:2259
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x43fe99
RSP: 002b:00007ffc46416548 EFLAGS: 00000207 ORIG_RAX: 000000000000002f
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fe99
RDX: 0000000000000000 RSI: 0000000020d63fc8 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000207 R12: 0000000000401800
R13: 0000000000401890 R14: 0000000000000000 R15: 0000000000000000
BUG: unable to handle kernel NULL pointer dereference at 0000000084b9663a
IP: virt_to_cache mm/slab.c:400 [inline]
IP: kfree+0xb2/0x250 mm/slab.c:3802
PGD 1cb57d067 P4D 1cb57d067 PUD 1cb57c067 PMD 0 
Oops: 0000 [#1] SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 0 PID: 3084 Comm: syzkaller938817 Not tainted 4.15.0-rc1+ #203
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: 000000003b250d90 task.stack: 000000005c2057e6
RIP: 0010:virt_to_cache mm/slab.c:400 [inline]
RIP: 0010:kfree+0xb2/0x250 mm/slab.c:3802
RSP: 0018:ffff8801cb587780 EFLAGS: 00010046
RAX: 0000000000000000 RBX: ffff8801cb587948 RCX: ffffffffffffffff
RDX: ffffea00072d61c0 RSI: 0000000000000000 RDI: ffff8801cb587948
RBP: ffff8801cb5877a0 R08: 1ffff100396b0ea2 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000286
R13: 0000000000000000 R14: ffff8801cb587948 R15: ffff8801cb5878b0
FS:  000000000091a880(0000) GS:ffff8801db400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000074 CR3: 00000001cb564000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 blkcipher_walk_done+0x72b/0xde0 crypto/blkcipher.c:139
 encrypt+0x50a/0xaf0 crypto/salsa20_generic.c:208
 skcipher_crypt_blkcipher crypto/skcipher.c:622 [inline]
 skcipher_decrypt_blkcipher+0x213/0x310 crypto/skcipher.c:640
 crypto_skcipher_decrypt include/crypto/skcipher.h:463 [inline]
 _skcipher_recvmsg crypto/algif_skcipher.c:144 [inline]
 skcipher_recvmsg+0xa54/0xf20 crypto/algif_skcipher.c:165
 sock_recvmsg_nosec net/socket.c:805 [inline]
 sock_recvmsg+0xc9/0x110 net/socket.c:812
 ___sys_recvmsg+0x29b/0x630 net/socket.c:2207
 __sys_recvmsg+0xe2/0x210 net/socket.c:2252
 SYSC_recvmsg net/socket.c:2264 [inline]
 SyS_recvmsg+0x2d/0x50 net/socket.c:2259
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x43fe99
RSP: 002b:00007ffc46416548 EFLAGS: 00000207 ORIG_RAX: 000000000000002f
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fe99
RDX: 0000000000000000 RSI: 0000000020d63fc8 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000207 R12: 0000000000401800
R13: 0000000000401890 R14: 0000000000000000 R15: 0000000000000000
Code: c2 48 b8 00 00 00 00 00 ea ff ff 48 89 df 48 c1 ea 0c 48 c1 e2 06 48 01 c2 48 8b 42 20 48 8d 48 ff a8 01 48 0f 45 d1 4c 8b 6a 30 <49> 63 75 74 e8 f5 76 af ff 48 89 de 4c 89 ef 4c 8b 75 08 e8 06 
RIP: virt_to_cache mm/slab.c:400 [inline] RSP: ffff8801cb587780
RIP: kfree+0xb2/0x250 mm/slab.c:3802 RSP: ffff8801cb587780
CR2: 0000000000000074
---[ end trace 52b07bdff7be1a6e ]---