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SubjectRe: crypto: deadlock between crypto_alg_sem/rtnl_mutex/genl_mutex
On Sun, Mar 5, 2017 at 4:08 PM, Dmitry Vyukov <dvyukov@google.com> wrote:
> Hello,
>
> I am getting the following deadlock reports while running syzkaller
> fuzzer on net-next/8d70eeb84ab277377c017af6a21d0a337025dede:
>
> ======================================================
> [ INFO: possible circular locking dependency detected ]
> 4.10.0+ #5 Not tainted
> -------------------------------------------------------
> syz-executor6/6143 is trying to acquire lock:
> (nlk->cb_mutex){+.+.+.}, at: [<ffffffff837df634>]
> __netlink_dump_start+0xf4/0x760 net/netlink/af_netlink.c:2187
>
> but task is already holding lock:
> (crypto_alg_sem){+++++.}, at: [<ffffffff821cd1f6>]
> crypto_user_rcv_msg+0x136/0x4f0 crypto/crypto_user.c:507
>
> which lock already depends on the new lock.
>
>
> the existing dependency chain (in reverse order) is:
>
> -> #4 (crypto_alg_sem){+++++.}:
> validate_chain kernel/locking/lockdep.c:2267 [inline]
> __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> down_read+0x9b/0x150 kernel/locking/rwsem.c:23
> crypto_alg_lookup+0x23/0x50 crypto/api.c:199
> crypto_larval_lookup.part.10+0x9a/0x3b0 crypto/api.c:217
> crypto_larval_lookup crypto/api.c:211 [inline]
> crypto_alg_mod_lookup+0x77/0x1b0 crypto/api.c:270
> crypto_alloc_base+0x50/0x1e0 crypto/api.c:416
> crypto_alloc_cipher include/linux/crypto.h:1407 [inline]
> tcp_fastopen_reset_cipher+0xc2/0x2e0 net/ipv4/tcp_fastopen.c:48
> tcp_fastopen_init_key_once+0x114/0x120 net/ipv4/tcp_fastopen.c:29
> do_tcp_setsockopt.isra.36+0x140a/0x20a0 net/ipv4/tcp.c:2684
> tcp_setsockopt+0xb0/0xd0 net/ipv4/tcp.c:2733
> sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2731
> SYSC_setsockopt net/socket.c:1786 [inline]
> SyS_setsockopt+0x25c/0x390 net/socket.c:1765
> entry_SYSCALL_64_fastpath+0x1f/0xc2
>
> -> #3 (sk_lock-AF_INET){+.+.+.}:
> validate_chain kernel/locking/lockdep.c:2267 [inline]
> __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> lock_sock_nested+0xcb/0x120 net/core/sock.c:2536
> lock_sock include/net/sock.h:1460 [inline]
> rds_tcp_listen_stop+0x57/0x140 net/rds/tcp_listen.c:284
> rds_tcp_kill_sock net/rds/tcp.c:529 [inline]
> rds_tcp_dev_event+0x383/0xc50 net/rds/tcp.c:568
> notifier_call_chain+0x1b5/0x2b0 kernel/notifier.c:93
> __raw_notifier_call_chain kernel/notifier.c:394 [inline]
> raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
> call_netdevice_notifiers_info+0x51/0x90 net/core/dev.c:1646
> call_netdevice_notifiers net/core/dev.c:1662 [inline]
> netdev_run_todo+0x3b2/0xa30 net/core/dev.c:7530
> rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:104
> default_device_exit_batch+0x504/0x620 net/core/dev.c:8334
> ops_exit_list.isra.6+0x100/0x150 net/core/net_namespace.c:144
> cleanup_net+0x551/0xa90 net/core/net_namespace.c:463
> process_one_work+0xbd0/0x1c10 kernel/workqueue.c:2096
> worker_thread+0x223/0x1990 kernel/workqueue.c:2230
> kthread+0x326/0x3f0 kernel/kthread.c:229
> ret_from_fork+0x31/0x40 arch/x86/entry/entry_64.S:430
>
> -> #2 (rtnl_mutex){+.+.+.}:
> validate_chain kernel/locking/lockdep.c:2267 [inline]
> __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> __mutex_lock_common kernel/locking/mutex.c:756 [inline]
> __mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
> mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
> rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
> tipc_nl_bearer_dump+0x3ef/0x720 net/tipc/bearer.c:774
> genl_lock_dumpit+0x68/0x90 net/netlink/genetlink.c:479
> netlink_dump+0x54d/0xd40 net/netlink/af_netlink.c:2127
> __netlink_dump_start+0x4e5/0x760 net/netlink/af_netlink.c:2217
> genl_family_rcv_msg+0xd9d/0x1040 net/netlink/genetlink.c:546
> genl_rcv_msg+0xa6/0x140 net/netlink/genetlink.c:620
> netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
> genl_rcv+0x28/0x40 net/netlink/genetlink.c:631
> netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
> netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
> netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
> sock_sendmsg_nosec net/socket.c:633 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:643
> sock_write_iter+0x326/0x600 net/socket.c:846
> call_write_iter include/linux/fs.h:1733 [inline]
> new_sync_write fs/read_write.c:497 [inline]
> __vfs_write+0x483/0x740 fs/read_write.c:510
> vfs_write+0x187/0x530 fs/read_write.c:558
> SYSC_write fs/read_write.c:605 [inline]
> SyS_write+0xfb/0x230 fs/read_write.c:597
> entry_SYSCALL_64_fastpath+0x1f/0xc2
>
> -> #1 (genl_mutex){+.+.+.}:
> validate_chain kernel/locking/lockdep.c:2267 [inline]
> __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> __mutex_lock_common kernel/locking/mutex.c:756 [inline]
> __mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
> mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
> genl_lock net/netlink/genetlink.c:32 [inline]
> genl_lock_dumpit+0x41/0x90 net/netlink/genetlink.c:478
> netlink_dump+0x54d/0xd40 net/netlink/af_netlink.c:2127
> __netlink_dump_start+0x4e5/0x760 net/netlink/af_netlink.c:2217
> genl_family_rcv_msg+0xd9d/0x1040 net/netlink/genetlink.c:546
> genl_rcv_msg+0xa6/0x140 net/netlink/genetlink.c:620
> netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
> genl_rcv+0x28/0x40 net/netlink/genetlink.c:631
> netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
> netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
> netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
> sock_sendmsg_nosec net/socket.c:633 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:643
> sock_write_iter+0x326/0x600 net/socket.c:846
> call_write_iter include/linux/fs.h:1733 [inline]
> new_sync_write fs/read_write.c:497 [inline]
> __vfs_write+0x483/0x740 fs/read_write.c:510
> vfs_write+0x187/0x530 fs/read_write.c:558
> SYSC_write fs/read_write.c:605 [inline]
> SyS_write+0xfb/0x230 fs/read_write.c:597
> entry_SYSCALL_64_fastpath+0x1f/0xc2
>
> -> #0 (nlk->cb_mutex){+.+.+.}:
> check_prev_add kernel/locking/lockdep.c:1830 [inline]
> check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
> validate_chain kernel/locking/lockdep.c:2267 [inline]
> __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> __mutex_lock_common kernel/locking/mutex.c:756 [inline]
> __mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
> mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
> __netlink_dump_start+0xf4/0x760 net/netlink/af_netlink.c:2187
> netlink_dump_start include/linux/netlink.h:165 [inline]
> crypto_user_rcv_msg+0x2ad/0x4f0 crypto/crypto_user.c:517
> netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
> crypto_netlink_rcv+0x2a/0x40 crypto/crypto_user.c:538
> netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
> netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
> netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
> sock_sendmsg_nosec net/socket.c:633 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:643
> ___sys_sendmsg+0x8fa/0x9f0 net/socket.c:1985
> __sys_sendmsg+0x138/0x300 net/socket.c:2019
> SYSC_sendmsg net/socket.c:2030 [inline]
> SyS_sendmsg+0x2d/0x50 net/socket.c:2026
> entry_SYSCALL_64_fastpath+0x1f/0xc2
>
> other info that might help us debug this:
>
> Chain exists of:
> nlk->cb_mutex --> sk_lock-AF_INET --> crypto_alg_sem
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(crypto_alg_sem);
> lock(sk_lock-AF_INET);
> lock(crypto_alg_sem);
> lock(nlk->cb_mutex);
>
> *** DEADLOCK ***
>
> 2 locks held by syz-executor6/6143:
> #0: (crypto_cfg_mutex){+.+...}, at: [<ffffffff821cad9b>]
> crypto_netlink_rcv+0x1b/0x40 crypto/crypto_user.c:537
> #1: (crypto_alg_sem){+++++.}, at: [<ffffffff821cd1f6>]
> crypto_user_rcv_msg+0x136/0x4f0 crypto/crypto_user.c:507
>
> stack backtrace:
> CPU: 0 PID: 6143 Comm: syz-executor6 Not tainted 4.10.0+ #5
> Hardware name: Google Google Compute Engine/Google Compute Engine,
> BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:16 [inline]
> dump_stack+0x2ee/0x3ef lib/dump_stack.c:52
> print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1204
> check_prev_add kernel/locking/lockdep.c:1830 [inline]
> check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
> validate_chain kernel/locking/lockdep.c:2267 [inline]
> __lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
> lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
> __mutex_lock_common kernel/locking/mutex.c:756 [inline]
> __mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
> mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
> __netlink_dump_start+0xf4/0x760 net/netlink/af_netlink.c:2187
> netlink_dump_start include/linux/netlink.h:165 [inline]
> crypto_user_rcv_msg+0x2ad/0x4f0 crypto/crypto_user.c:517
> netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
> crypto_netlink_rcv+0x2a/0x40 crypto/crypto_user.c:538
> netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
> netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
> netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
> sock_sendmsg_nosec net/socket.c:633 [inline]
> sock_sendmsg+0xca/0x110 net/socket.c:643
> ___sys_sendmsg+0x8fa/0x9f0 net/socket.c:1985
> __sys_sendmsg+0x138/0x300 net/socket.c:2019
> SYSC_sendmsg net/socket.c:2030 [inline]
> SyS_sendmsg+0x2d/0x50 net/socket.c:2026
> entry_SYSCALL_64_fastpath+0x1f/0xc2



Another one involving tcp_md5sig_mutex:


======================================================
[ INFO: possible circular locking dependency detected ]
SELinux: unrecognized netlink message: protocol=9 nlmsg_type=2
sclass=netlink_audit_socket pig=4033 comm=syz-executor4
4.10.0+ #5 Not tainted
-------------------------------------------------------
syz-executor8/4018 is trying to acquire lock:
(crypto_alg_sem){++++++}, at: [<ffffffff82193473>]
crypto_alg_lookup+0x23/0x50 crypto/api.c:199

but task is already holding lock:
(tcp_md5sig_mutex){+.+...}, at: [<ffffffff838e4efa>]
tcp_alloc_md5sig_pool+0x4a/0x470 net/ipv4/tcp.c:3196

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #5 (tcp_md5sig_mutex){+.+...}:
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
tcp_alloc_md5sig_pool+0x4a/0x470 net/ipv4/tcp.c:3196
tcp_md5_do_add+0x1d8/0x5d0 net/ipv4/tcp_ipv4.c:969
tcp_v4_parse_md5_keys+0x1c7/0x2b0 net/ipv4/tcp_ipv4.c:1037
do_tcp_setsockopt.isra.36+0x657/0x20a0 net/ipv4/tcp.c:2668
tcp_setsockopt+0xb0/0xd0 net/ipv4/tcp.c:2733
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2731
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281
return_from_SYSCALL_64+0x0/0x7a

-> #4 (sk_lock-AF_INET){+.+.+.}:
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
lock_sock_nested+0xcb/0x120 net/core/sock.c:2536
lock_sock include/net/sock.h:1460 [inline]
do_ip_setsockopt.isra.12+0x301/0x3760 net/ipv4/ip_sockglue.c:653
ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1265
tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2731
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2731
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
entry_SYSCALL_64_fastpath+0x1f/0xc2

-> #3 (rtnl_mutex){+.+.+.}:
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
nl80211_prepare_wdev_dump.isra.37+0x2c/0x5d0 net/wireless/nl80211.c:548
nl80211_dump_station+0x178/0xd80 net/wireless/nl80211.c:4455
genl_lock_dumpit+0x68/0x90 net/netlink/genetlink.c:479
netlink_dump+0x54d/0xd40 net/netlink/af_netlink.c:2127
__netlink_dump_start+0x4e5/0x760 net/netlink/af_netlink.c:2217
genl_family_rcv_msg+0xd9d/0x1040 net/netlink/genetlink.c:546
genl_rcv_msg+0xa6/0x140 net/netlink/genetlink.c:620
netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
genl_rcv+0x28/0x40 net/netlink/genetlink.c:631
netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
sock_write_iter+0x326/0x600 net/socket.c:846
call_write_iter include/linux/fs.h:1733 [inline]
new_sync_write fs/read_write.c:497 [inline]
__vfs_write+0x483/0x740 fs/read_write.c:510
vfs_write+0x187/0x530 fs/read_write.c:558
SYSC_write fs/read_write.c:605 [inline]
SyS_write+0xfb/0x230 fs/read_write.c:597
entry_SYSCALL_64_fastpath+0x1f/0xc2

-> #2 (genl_mutex){+.+.+.}:
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
genl_lock net/netlink/genetlink.c:32 [inline]
genl_lock_dumpit+0x41/0x90 net/netlink/genetlink.c:478
netlink_dump+0x54d/0xd40 net/netlink/af_netlink.c:2127
__netlink_dump_start+0x4e5/0x760 net/netlink/af_netlink.c:2217
genl_family_rcv_msg+0xd9d/0x1040 net/netlink/genetlink.c:546
genl_rcv_msg+0xa6/0x140 net/netlink/genetlink.c:620
netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
genl_rcv+0x28/0x40 net/netlink/genetlink.c:631
netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
sock_write_iter+0x326/0x600 net/socket.c:846
call_write_iter include/linux/fs.h:1733 [inline]
new_sync_write fs/read_write.c:497 [inline]
__vfs_write+0x483/0x740 fs/read_write.c:510
vfs_write+0x187/0x530 fs/read_write.c:558
SYSC_write fs/read_write.c:605 [inline]
SyS_write+0xfb/0x230 fs/read_write.c:597
entry_SYSCALL_64_fastpath+0x1f/0xc2

-> #1 (nlk->cb_mutex){+.+.+.}:
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
__mutex_lock_common kernel/locking/mutex.c:756 [inline]
__mutex_lock+0x172/0x1730 kernel/locking/mutex.c:893
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
__netlink_dump_start+0xf4/0x760 net/netlink/af_netlink.c:2187
netlink_dump_start include/linux/netlink.h:165 [inline]
crypto_user_rcv_msg+0x2ad/0x4f0 crypto/crypto_user.c:517
netlink_rcv_skb+0x2ab/0x390 net/netlink/af_netlink.c:2298
crypto_netlink_rcv+0x2a/0x40 crypto/crypto_user.c:538
netlink_unicast_kernel net/netlink/af_netlink.c:1231 [inline]
netlink_unicast+0x514/0x730 net/netlink/af_netlink.c:1257
netlink_sendmsg+0xa9f/0xe50 net/netlink/af_netlink.c:1803
sock_sendmsg_nosec net/socket.c:633 [inline]
sock_sendmsg+0xca/0x110 net/socket.c:643
___sys_sendmsg+0x8fa/0x9f0 net/socket.c:1985
__sys_sendmsg+0x138/0x300 net/socket.c:2019
SYSC_sendmsg net/socket.c:2030 [inline]
SyS_sendmsg+0x2d/0x50 net/socket.c:2026
entry_SYSCALL_64_fastpath+0x1f/0xc2

-> #0 (crypto_alg_sem){++++++}:
check_prev_add kernel/locking/lockdep.c:1830 [inline]
check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
down_read+0x9b/0x150 kernel/locking/rwsem.c:23
crypto_alg_lookup+0x23/0x50 crypto/api.c:199
crypto_larval_lookup.part.10+0x9a/0x3b0 crypto/api.c:217
crypto_larval_lookup crypto/api.c:211 [inline]
crypto_alg_mod_lookup+0x77/0x1b0 crypto/api.c:270
crypto_find_alg crypto/api.c:500 [inline]
crypto_alloc_tfm+0x101/0x2e0 crypto/api.c:533
crypto_alloc_ahash+0x2c/0x40 crypto/ahash.c:525
__tcp_alloc_md5sig_pool net/ipv4/tcp.c:3158 [inline]
tcp_alloc_md5sig_pool+0x85/0x470 net/ipv4/tcp.c:3199
tcp_md5_do_add+0x1d8/0x5d0 net/ipv4/tcp_ipv4.c:969
tcp_v4_parse_md5_keys+0x1c7/0x2b0 net/ipv4/tcp_ipv4.c:1037
do_tcp_setsockopt.isra.36+0x657/0x20a0 net/ipv4/tcp.c:2668
tcp_setsockopt+0xb0/0xd0 net/ipv4/tcp.c:2733
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2731
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281
return_from_SYSCALL_64+0x0/0x7a

other info that might help us debug this:

Chain exists of:
crypto_alg_sem --> sk_lock-AF_INET --> tcp_md5sig_mutex

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(tcp_md5sig_mutex);
lock(sk_lock-AF_INET);
lock(tcp_md5sig_mutex);
lock(crypto_alg_sem);

*** DEADLOCK ***

2 locks held by syz-executor8/4018:
#0: (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff838e7a26>] lock_sock
include/net/sock.h:1460 [inline]
#0: (sk_lock-AF_INET){+.+.+.}, at: [<ffffffff838e7a26>]
do_tcp_setsockopt.isra.36+0x216/0x20a0 net/ipv4/tcp.c:2466
#1: (tcp_md5sig_mutex){+.+...}, at: [<ffffffff838e4efa>]
tcp_alloc_md5sig_pool+0x4a/0x470 net/ipv4/tcp.c:3196

stack backtrace:
CPU: 0 PID: 4018 Comm: syz-executor8 Not tainted 4.10.0+ #5
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x2ee/0x3ef lib/dump_stack.c:52
print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1204
check_prev_add kernel/locking/lockdep.c:1830 [inline]
check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1940
validate_chain kernel/locking/lockdep.c:2267 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3340
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3755
down_read+0x9b/0x150 kernel/locking/rwsem.c:23
crypto_alg_lookup+0x23/0x50 crypto/api.c:199
crypto_larval_lookup.part.10+0x9a/0x3b0 crypto/api.c:217
crypto_larval_lookup crypto/api.c:211 [inline]
crypto_alg_mod_lookup+0x77/0x1b0 crypto/api.c:270
crypto_find_alg crypto/api.c:500 [inline]
crypto_alloc_tfm+0x101/0x2e0 crypto/api.c:533
crypto_alloc_ahash+0x2c/0x40 crypto/ahash.c:525
__tcp_alloc_md5sig_pool net/ipv4/tcp.c:3158 [inline]
tcp_alloc_md5sig_pool+0x85/0x470 net/ipv4/tcp.c:3199
tcp_md5_do_add+0x1d8/0x5d0 net/ipv4/tcp_ipv4.c:969
tcp_v4_parse_md5_keys+0x1c7/0x2b0 net/ipv4/tcp_ipv4.c:1037
do_tcp_setsockopt.isra.36+0x657/0x20a0 net/ipv4/tcp.c:2668
tcp_setsockopt+0xb0/0xd0 net/ipv4/tcp.c:2733
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2731
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
do_syscall_64+0x2e8/0x930 arch/x86/entry/common.c:281

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