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[34.85.235.172]) by smtp.gmail.com with ESMTPSA id 00721157ae682-81f33ee52a0sm13947347b3.36.2026.07.22.07.26.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jul 2026 07:26:23 -0700 (PDT) Date: Wed, 22 Jul 2026 10:26:23 -0400 From: Willem de Bruijn To: Daniel Zahka , Qihang , netdev@vger.kernel.org Cc: willemdebruijn.kernel@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, stable@vger.kernel.org Message-ID: In-Reply-To: <3e4b1552-57d4-42ad-a244-a91b74b8dae1@gmail.com> References: <20260721084935.12312-1-q.h.hack.winter@gmail.com> <3e4b1552-57d4-42ad-a244-a91b74b8dae1@gmail.com> Subject: Re: [PATCH net] packet: use a consistent hard_header_len in send paths Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Daniel Zahka wrote: > > > On 7/21/26 4:49 AM, Qihang wrote: > > packet_snd() and tpacket_snd() read dev->hard_header_len multiple times > > while building an skb. Device reconfiguration can change this value > > concurrently, for example through bonding device type changes. > > > > For SOCK_RAW, packet_snd() stores the first value in reserve, later > > allocates headroom using LL_RESERVED_SPACE(dev), and then subtracts > > reserve from the skb headroom. If hard_header_len decreases between the > > reads, the skb can be allocated with less headroom than reserve, moving > > skb->data before skb->head. The subsequent skb_copy_datagram_from_iter() > > can then attempt an out-of-bounds copy. Hardened usercopy catches this as > > a kernel memory overwrite attempt. > > > > Wouldn't there be a similar issue in the SOCK_DGRAM path with > dev_hard_header() calling skb_push() after packet_alloc_skb()? Good point. this does not use hard_header_len directly, but e.g., eth_header() assumes ETH_HLEN is available to push. Simply caching hard_header_len won't resolve this. dev->hard_header_len and dev->header_ops (incl .create) are not updated atomically. I missed this earlier, but besides packet_snd and tpacket_snd, the fix is also needed by packet_sendmsg_spkt.