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[34.48.4.250]) by smtp.gmail.com with ESMTPSA id 00721157ae682-81fa25ed2bbsm5648227b3.0.2026.07.28.13.25.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jul 2026 13:25:37 -0700 (PDT) Date: Tue, 28 Jul 2026 16:25:36 -0400 From: Willem de Bruijn To: Qihang , netdev@vger.kernel.org Cc: willemdebruijn.kernel@gmail.com, daniel.zahka@gmail.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, stable@vger.kernel.org, Qihang Message-ID: In-Reply-To: <20260728031345.49562-2-q.h.hack.winter@gmail.com> References: <20260726092110.80185-1-q.h.hack.winter@gmail.com> <20260728031345.49562-1-q.h.hack.winter@gmail.com> <20260728031345.49562-2-q.h.hack.winter@gmail.com> Subject: Re: [PATCH net v3 1/2] packet: use consistent hard_header_len in non-ring 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 Qihang wrote: > packet_snd() reads dev->hard_header_len multiple times while allocating > and constructing an skb. Device reconfiguration can change this value > concurrently, for example through bonding device type changes. > > For SOCK_RAW, packet_snd() can save a larger value in reserve and later > allocate headroom using a smaller value. Moving skb->data back by reserve > then places it before skb->head, and the following copy from userspace can > attempt an out-of-bounds write. > > packet_sendmsg_spkt() has the same issue because it calculates its > reservation and header offset from separate reads before dropping the RCU > read lock to allocate the skb. > > Add LL_RESERVED_SPACE_EX() for callers that already saved a header length. > Read hard_header_len once in packet_snd() and use it for allocation and > construction. In packet_sendmsg_spkt(), preserve the allocation-time value > through the device lookup retry. > > The separate SOCK_DGRAM consistency problem between hard_header_len and > header_ops->create is not addressed here. > > Fixes: b84bbaf7a6c8 ("packet: in packet_snd start writing at link layer allocation") > Cc: stable@vger.kernel.org > Signed-off-by: Qihang Reviewed-by: Willem de Bruijn New revisions should not be sent as a reply to an existing thread.