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[34.85.134.180]) by smtp.gmail.com with ESMTPSA id 00721157ae682-79b1e3bec5dsm35125117b3.25.2026.03.27.12.56.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Mar 2026 12:56:48 -0700 (PDT) Date: Fri, 27 Mar 2026 15:56:47 -0400 From: Willem de Bruijn To: Guoyu Su , edumazet@google.com, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com Cc: willemdebruijn.kernel@gmail.com, netdev@vger.kernel.org, horms@kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, syzbot+1543a7d954d9c6d00407@syzkaller.appspotmail.com, Guoyu Su Message-ID: In-Reply-To: <20260327153507.39742-1-yss2813483011xxl@gmail.com> References: <20260327153507.39742-1-yss2813483011xxl@gmail.com> Subject: Re: [PATCH net v7] net: use skb_header_pointer() for TCPv4 GSO frag_off check 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 Guoyu Su wrote: > Syzbot reported a KMSAN uninit-value warning in gso_features_check() > called from netif_skb_features() [1]. > > gso_features_check() reads iph->frag_off to decide whether to clear > mangleid_features. Accessing the IPv4 header via ip_hdr()/inner_ip_hdr() > can rely on skb header offsets that are not always safe for direct > dereference on packets injected from PF_PACKET paths. > > Use skb_header_pointer() for the TCPv4 frag_off check so the header read > is robust whether data is already linear or needs copying. > > [1] https://syzkaller.appspot.com/bug?extid=1543a7d954d9c6d00407 > > Link: https://lore.kernel.org/netdev/willemdebruijn.kernel.1a9f35039caab@gmail.com/ > Fixes: cbc53e08a793 ("GSO: Add GSO type for fixed IPv4 ID") > Reported-by: syzbot+1543a7d954d9c6d00407@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=1543a7d954d9c6d00407 > Tested-by: syzbot+1543a7d954d9c6d00407@syzkaller.appspotmail.com > Signed-off-by: Guoyu Su Reviewed-by: Willem de Bruijn Sashiko asks about similar inner_ip_hdr in skb_gso_has_extension_hdr, but userspace cannot set skb->encapsulation, so that's a false positive.