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[34.48.4.250]) by smtp.gmail.com with ESMTPSA id 00721157ae682-823f09910b2sm59898947b3.16.2026.08.10.11.10.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Aug 2026 11:10:58 -0700 (PDT) Date: Mon, 10 Aug 2026 14:10:58 -0400 From: Willem de Bruijn To: Eric Dumazet , "David S . Miller" , Jakub Kicinski , Paolo Abeni Cc: Simon Horman , Kuniyuki Iwashima , Willem de Bruijn , netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet , syzbot+30b93b6845b19cc38581@syzkaller.appspotmail.com Message-ID: In-Reply-To: <20260810150447.1220864-1-edumazet@google.com> References: <20260810150447.1220864-1-edumazet@google.com> Subject: Re: [PATCH net] af_packet: Don't send zero-byte data in tpacket_snd(). Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Eric Dumazet wrote: > 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