On Mon, Jun 29, 2026 at 11:24:49AM -0700, Alexei Starovoitov wrote:
On Mon Jun 29, 2026 at 10:27 AM PDT, Sechang Lim wrote:
sock_map_update_common() and __sock_map_delete() hold stab->lock and call
sock_map_unref() -> sock_map_del_link(), which takes sk_callback_lock for
write. That gives the order stab->lock -> sk_callback_lock.
The reverse order comes from the SK_SKB stream parser.
sk_psock_strp_data_ready() holds sk_callback_lock for read, and after the
verdict tcp_bpf_strp_read_sock() acks the consumed data inline via
__tcp_cleanup_rbuf(). The ACK goes out egress, where a sched_cls program
deletes from the sockmap and takes stab->lock:
WARNING: possible circular locking dependency detected
------------------------------------------------------
syz.9.8824 is trying to acquire lock:
(&stab->lock){+.-.}-{3:3}, at: __sock_map_delete net/core/sock_map.c:421
but task is already holding lock:
(clock-AF_INET){++.-}-{3:3}, at: sk_psock_strp_data_ready
net/core/skmsg.c:1173
-> #1 (clock-AF_INET){++.-}-{3:3}:
_raw_write_lock_bh
sock_map_del_link net/core/sock_map.c:167
sock_map_unref net/core/sock_map.c:184
sock_map_update_common net/core/sock_map.c:509
sock_map_update_elem_sys net/core/sock_map.c:588
map_update_elem kernel/bpf/syscall.c:1805
-> #0 (&stab->lock){+.-.}-{3:3}:
_raw_spin_lock_bh
__sock_map_delete net/core/sock_map.c:421
sock_map_delete_elem net/core/sock_map.c:452
bpf_prog_06044d24140080b6
tcx_run net/core/dev.c:4451
sch_handle_egress net/core/dev.c:4541
__dev_queue_xmit net/core/dev.c:4808
...
tcp_bpf_strp_read_sock net/ipv4/tcp_bpf.c:701
strp_data_ready net/strparser/strparser.c:402
sk_psock_strp_data_ready net/core/skmsg.c:1174
tcp_data_queue net/ipv4/tcp_input.c:5661
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
rlock(clock-AF_INET);
lock(&stab->lock);
lock(clock-AF_INET);
lock(&stab->lock);
*** DEADLOCK ***
A tc, xdp or flow_dissector program has no reason to update or delete a
sockmap, and redirect does not go through here. Drop them from
may_update_sockmap() so the verifier rejects it. It also closes the
matching sockhash inversion.
Suggested-by: John Fastabend <[email protected]>
Signed-off-by: Sechang Lim <[email protected]>
John,
please ack.
Hi Sechang,
I think we additionally need to also block BPF_PROG_TYPE_SOCKET_FILTER?
Did you check this case I guess the same case is possible there?
Then another patch needs to restrict BPF_SOCK_OPS users. For that
we need to block BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_*.
Let me know if you want to do those as well. Let me know if you want
to do both patches or just the prog blocking above with the possible
addition of SOCKET_FILTER. I didn't search very hard so probably need
to check all the BPF_SOCK_OPS_* to find the valid cases.
Thanks,
John
