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[34.85.165.172]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-65314b63174sm1219116d50.6.2026.04.17.13.01.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 17 Apr 2026 13:01:12 -0700 (PDT) Date: Fri, 17 Apr 2026 16:01:12 -0400 From: Willem de Bruijn To: Zero Mark , Willem de Bruijn Cc: security@kernel.org, "David S . Miller" , Jakub Kicinski , Eric Dumazet , netdev@vger.kernel.org, Zero Mark Message-ID: In-Reply-To: <20260417133610.88158-1-patzilla007@gmail.com> References: <20260417133610.88158-1-patzilla007@gmail.com> Subject: Re: [PATCH net] net/packet: fix TOCTOU race on mmap'd vnet_hdr 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 Zero Mark wrote: > In tpacket_snd(), when PACKET_VNET_HDR is enabled, vnet_hdr points > directly into the mmap'd TX ring buffer shared with userspace. The > kernel validates the header via __packet_snd_vnet_parse() but then > re-reads all fields later in virtio_net_hdr_to_skb(). A concurrent > userspace thread can modify the vnet_hdr fields between validation > and use, bypassing all safety checks. > > The non-TPACKET path (packet_snd()) already correctly copies vnet_hdr > to a stack-local variable. All other vnet_hdr consumers in the kernel > (tun.c, tap.c, virtio_net.c) also use stack copies. The TPACKET TX > path is the only caller of virtio_net_hdr_to_skb() that reads directly > from user-controlled shared memory. > > Fix this by copying vnet_hdr from the mmap'd ring buffer to a > stack-local variable before validation and use, consistent with the > approach used in packet_snd() and all other callers. > > Fixes: 1d036d25e560 ("packet: tpacket_snd gso and checksum offload") > Signed-off-by: Zero Mark Reviewed-by: Willem de Bruijn