CVE-2026-52942

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

netfilter: nf_log: validate MAC header was set before dumping it

The fallback path of dump_mac_header() guards the MAC header access

only with "skb->mac_header != skb->network_header", without checking

skb_mac_header_was_set(). When the MAC header is unset, mac_header is

0xffff, so the test passes and skb_mac_header(skb) returns

skb->head + 0xffff, ~64 KiB past the buffer; the loop then reads

dev->hard_header_len bytes out of bounds into the kernel log.

This is reachable via the netdev logger: nf_log_unknown_packet() calls

dump_mac_header() unconditionally, and an skb sent through AF_PACKET

with PACKET_QDISC_BYPASS reaches the egress hook with mac_header still

unset (__dev_queue_xmit(), which would reset it, is bypassed).

Add the skb_mac_header_was_set() check the ARPHRD_ETHER path already

uses, and replace the open-coded MAC header length test with

skb_mac_header_len(). Only skbs with an unset MAC header are affected;

valid ones are dumped as before.

BUG: KASAN: slab-out-of-bounds in dump_mac_header (net/netfilter/nf_log_syslog.c:831)

Read of size 1 at addr ffff88800ea49d3f by task exploit/148

Call Trace:

kasan_report (mm/kasan/report.c:595)

dump_mac_header (net/netfilter/nf_log_syslog.c:831)

nf_log_netdev_packet (net/netfilter/nf_log_syslog.c:938 net/netfilter/nf_log_syslog.c:963)

nf_log_packet (net/netfilter/nf_log.c:260)

nft_log_eval (net/netfilter/nft_log.c:60)

nft_do_chain (net/netfilter/nf_tables_core.c:285)

nft_do_chain_netdev (net/netfilter/nft_chain_filter.c:307)

nf_hook_slow (net/netfilter/core.c:619)

nf_hook_direct_egress (net/packet/af_packet.c:257)

packet_xmit (net/packet/af_packet.c:280)

packet_sendmsg (net/packet/af_packet.c:3114)

__sys_sendto (net/socket.c:2265)