On 31/08/2026 15:25, Ido Schimmel wrote:
On Mon, Aug 31, 2026 at 07:30:51PM +0800, Zhao ShiRong wrote:
Packets locally delivered by the bridge are re-injected into the
receive path via br_pass_frame_up() -> br_netif_receive_skb() ->
netif_receive_skb() with skb->dev set to the bridge device. If the
bridge device has an XDP program attached, __netif_receive_skb_core()
runs do_xdp_generic() a second time on such packets.
A locally-delivered packet that was allocated on the TX path (e.g. an
MLD packet built by mld_newpack()) does not carry the
XDP_PACKET_HEADROOM that generic XDP requires, so
netif_skb_check_for_xdp() calls pskb_expand_head() and reallocates the
skb head buffer. This frees the head that the bridge rx path
(br_handle_frame() / br_handle_frame_finish()) is still using, leading
to a use-after-free read in br_handle_frame():
BUG: KASAN: slab-use-after-free in is_multicast_ether_addr [inline]
BUG: KASAN: slab-use-after-free in is_valid_ether_addr [inline]
BUG: KASAN: slab-use-after-free in br_handle_frame+0xcfb/0x1510
net/bridge/br_input.c:349
netif_receive_generic_xdp() already refuses to run generic XDP on
reinjected packets by checking skb_is_redirected(). Reuse that marker:
set it right before the bridge re-injects the packet, so generic XDP is
skipped and the head buffer is left intact.
Reported-by: [email protected]
Link:
https://lore.kernel.org/all/[email protected]/T/
Signed-off-by: Zhao ShiRong <[email protected]>
Eric sent a fix for this issue earlier today:
https://lore.kernel.org/netdev/[email protected]/
Oh I missed that patch, it fixes the root cause and we don't have to do
anything in
the bridge. Good thing :)
Thanks,
Nik
