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On the UDP receive path skb->dev is repurposed as dev_scratch (the
truesize/state cache set by udp_set_dev_scratch()), through the
union { struct net_device *dev; unsigned long dev_scratch; } in sk_buff.
When a UDP socket is in a sockmap, sk_data_ready is
sk_psock_verdict_data_ready(), which calls udp_read_skb() -> recv_actor()
(sk_psock_verdict_recv) to run the attached SK_SKB verdict program in softirq.
If that program calls a socket-lookup helper (bpf_sk_lookup_tcp/udp,
bpf_skc_lookup_tcp), bpf_skc_lookup() does:
if (skb->dev)
caller_net = dev_net(skb->dev);
skb->dev still holds the dev_scratch value (a non-NULL integer), so dev_net()
dereferences it as a struct net_device * and the kernel takes a general
protection fault on a non-canonical address in softirq:
Oops: general protection fault, probably for non-canonical address 0x1010000800004a0
CPU: 1 UID: 0 PID: 1406 Comm: syz.2.19 Not tainted 7.1.0-rc6 #1 PREEMPT(full)
RIP: 0010:bpf_skc_lookup net/core/filter.c:7033 [inline]
RIP: 0010:bpf_sk_lookup+0x45/0x160 net/core/filter.c:7047
Call Trace:
<IRQ>
bpf_prog_4675cb904b7071f8+0x12e/0x14e
bpf_prog_run_pin_on_cpu+0xc6/0x1f0
sk_psock_verdict_recv+0x1ba/0x350
udp_read_skb+0x31a/0x370
sk_psock_verdict_data_ready+0x2e3/0x600
__udp_enqueue_schedule_skb+0x4c8/0x650
udpv6_queue_rcv_one_skb+0x3ec/0x740
udp6_unicast_rcv_skb+0x11d/0x140
ip6_protocol_deliver_rcu+0x61e/0x950
ip6_input_finish+0xa9/0x150
NF_HOOK+0x286/0x2f0
ip6_input+0x117/0x220
NF_HOOK+0x286/0x2f0
__netif_receive_skb+0x85/0x200
process_backlog+0x374/0x9a0
__napi_poll+0x4f/0x1c0
net_rx_action+0x3b0/0x770
handle_softirqs+0x15a/0x460
do_softirq+0x57/0x80
</IRQ>
The rmem charge that dev_scratch accounted for is released by skb_recv_udp() on
dequeue, just above, so the scratch is dead by the time recv_actor() runs. Clear
skb->dev so bpf_skc_lookup() falls back to sock_net(skb->sk), which
skb_set_owner_sk_safe() set just above.
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| io_uring | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| rust | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .clippy.toml | ||
| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
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