Re: [PATCH net] macsec: don't read an unset MAC header in macsec_encrypt()

[Sabrina Dubroca <sd@queasysnail.net>]

2026-07-03, 17:36:33 +0900, Daehyeon Ko wrote:
> macsec_encrypt() reads the Ethernet header via eth_hdr(skb)
> (skb->head + skb->mac_header) to memmove() the 12 source/destination MAC
> bytes forward and make room for the SecTAG.
> 
> On the AF_PACKET SOCK_RAW + PACKET_QDISC_BYPASS transmit path the skb
> reaches the macsec ndo_start_xmit() with the MAC header unset, so
> eth_hdr(skb) resolves to skb->head + (u16)~0 and the read is out of
> bounds: a 12-byte heap over-read that is also emitted on the wire as the
> frame's outer source/destination MAC. KASAN reports a slab-out-of-bounds
> read in macsec_start_xmit() on 6.0; on current mainline a CONFIG_DEBUG_NET
> build flags it as an unset mac header in skb_mac_header().
> 
> On the TX path the L2 header is at skb->data, so use skb_eth_hdr(), added
> by commit 96cc4b69581d ("macvlan: do not assume mac_header is set in
> macvlan_broadcast()") for exactly this purpose.
> 
> Fixes: c09440f7dcb3 ("macsec: introduce IEEE 802.1AE driver")
> Cc: stable@vger.kernel.org
> Signed-off-by: Daehyeon Ko <4ncienth@gmail.com>
> ---
>  drivers/net/macsec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>

-- 
Sabrina