CVE-2026-53184

In the Linux kernel, the following vulnerability has been resolved:

udp: clear skb->dev before running a sockmap verdict

On the UDP receive path skb->dev is repurposed as devscratch (the truesize/state cache set by udpsetdevscratch()), through the union { struct netdevice *dev; unsigned long devscratch; } in sk_buff.

When a UDP socket is in a sockmap, skdataready is skpsockverdictdataready(), which calls udpreadskb() -> recvactor() (skpsockverdictrecv) to run the attached SKSKB verdict program in softirq. If that program calls a socket-lookup helper (bpfsklookuptcp/udp, bpfskclookuptcp), bpfskc_lookup() does:

if (skb->dev)
    caller_net = dev_net(skb->dev);

skb->dev still holds the devscratch value (a non-NULL integer), so devnet() 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:bpfskclookup net/core/filter.c:7033 [inline] RIP: 0010:bpfsklookup+0x45/0x160 net/core/filter.c:7047 Call Trace: <IRQ> bpfprog4675cb904b7071f8+0x12e/0x14e bpfprogrunpinoncpu+0xc6/0x1f0 skpsockverdictrecv+0x1ba/0x350 udpreadskb+0x31a/0x370 skpsockverdictdataready+0x2e3/0x600 __udpenqueuescheduleskb+0x4c8/0x650 udpv6queuercvoneskb+0x3ec/0x740 udp6unicastrcvskb+0x11d/0x140 ip6protocoldeliverrcu+0x61e/0x950 ip6inputfinish+0xa9/0x150 NFHOOK+0x286/0x2f0 ip6input+0x117/0x220 NFHOOK+0x286/0x2f0 __netifreceiveskb+0x85/0x200 process_backlog+0x374/0x9a0 _napipoll+0x4f/0x1c0 netrxaction+0x3b0/0x770 handlesoftirqs+0x15a/0x460 dosoftirq+0x57/0x80 </IRQ>

The rmem charge that devscratch accounted for is released by skbrecvudp() on dequeue, just above, so the scratch is dead by the time recvactor() runs. Clear skb->dev so bpfskclookup() falls back to socknet(skb->sk), which skbsetownersk_safe() set just above.