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[34.48.4.250]) by smtp.gmail.com with ESMTPSA id 00721157ae682-820134ccc5csm32130237b3.43.2026.08.05.20.07.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Aug 2026 20:07:23 -0700 (PDT) Date: Wed, 05 Aug 2026 23:07:22 -0400 From: Willem de Bruijn To: Qihang , netdev@vger.kernel.org Cc: willemdebruijn.kernel@gmail.com, willemb@google.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 Tang Message-ID: In-Reply-To: <20260805125729.19220-2-q.h.hack.winter@gmail.com> References: <20260805125729.19220-1-q.h.hack.winter@gmail.com> <20260805125729.19220-2-q.h.hack.winter@gmail.com> Subject: Re: [PATCH net v6 1/3] net: remove CAP_SYS_RAWIO zero-padding in dev_validate_header 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: > From: Qihang Tang > > dev_validate_header() reads dev->hard_header_len directly when > zero-padding short link layer headers for CAP_SYS_RAWIO holders: > > if (capable(CAP_SYS_RAWIO)) { > memset(ll_header + len, 0, dev->hard_header_len - len); > return true; > } > > Packet send paths call dev_validate_header() on skbs whose headroom was > allocated from an earlier hard_header_len read. If the device is > reconfigured so that dev->hard_header_len increases before validation, > the memset writes past the reserved buffer, an out-of-bounds write. > > This out-of-bounds write is masked in some SOCK_RAW paths today because > the same concurrent increase can first make skb_push() exceed the > reserved headroom and trigger skb_under_panic(). Remove the zero-padding > branch before making those hard_header_len reads consistent, so the > snapshot fixes do not turn a loud panic into a silent overwrite. > > This path is only reached for variable length L2 protocols, where > len < hard_header_len but len >= min_header_len. No remaining in-tree > variable length L2 protocol implements header_ops->validate, and the > CAP_SYS_RAWIO bypass that zero-pads and accepts short headers has no > real value beyond allowing testing of intentionally malformed input. > > Drop the CAP_SYS_RAWIO branch. The remaining reads of > dev->hard_header_len in dev_validate_header() are comparisons only and > have no memory safety impact. > > Suggested-by: Willem de Bruijn > Fixes: 2793a23aacbd ("net: validate variable length ll headers") > Cc: stable@vger.kernel.org > Signed-off-by: Qihang Tang Reviewed-by: Willem de Bruijn