From: Eric Dumazet Date: Mon, 10 Aug 2026 15:04:47 +0000 (+0000) Subject: af_packet: Don't send zero-byte data in tpacket_snd(). X-Git-Tag: v7.2~27^2~11 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6bcd76c134c55c697148acb5c0194e9666abdf84;p=thirdparty%2Fkernel%2Flinux.git af_packet: Don't send zero-byte data in tpacket_snd(). syzbot reported a WARNING in __dev_queue_xmit() triggered via tpacket_snd(): skb_assert_len WARNING: at include/linux/skbuff.h:2753 skb_assert_len WARNING: at __dev_queue_xmit+0x21bc/0x4970 net/core/dev.c:4781 Call Trace: dev_queue_xmit include/linux/netdevice.h:3448 [inline] packet_xmit+0x243/0x310 net/packet/af_packet.c:276 tpacket_snd net/packet/af_packet.c:2907 [inline] packet_sendmsg+0x28d6/0x4eb0 net/packet/af_packet.c:3134 When sending 0-byte packets via TPACKET ring buffer on devices with no hard header (e.g. dev->hard_header_len == 0), tpacket_fill_skb() populates an skb with skb->len == 0 and returns 0. tpacket_snd() then forwards this empty skb to packet_xmit(), causing __dev_queue_xmit() to hit skb_assert_len(skb). Similar checks exist in packet_snd() via commit dc633700f00f ("net/af_packet: check len when min_header_len equals to 0") and in packet_sendmsg_spkt() via commit 6a341729fb31 ("af_packet: Don't send zero-byte data in packet_sendmsg_spkt()."). Return -EINVAL in tpacket_fill_skb() when skb->len is zero to reject zero-length packets in tpacket_snd(). Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Reported-by: syzbot+30b93b6845b19cc38581@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/6a79e807.01d0871a.3a0d52.00ac.GAE@google.com/T/#u Signed-off-by: Eric Dumazet Reviewed-by: Willem de Bruijn Reviewed-by: Jiayuan Chen Link: https://patch.msgid.link/20260810150447.1220864-1-edumazet@google.com Signed-off-by: Jakub Kicinski --- diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 213a8a3b7ee5..1168bd6b09cd 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -2660,6 +2660,9 @@ static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb, len = ((to_write > len_max) ? len_max : to_write); } + if (unlikely(!skb->len)) + return -EINVAL; + packet_parse_headers(skb, sock); return tp_len;