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[108.214.96.168]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-2c3c41c1547sm4529655eec.7.2026.03.29.05.51.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 29 Mar 2026 05:51:33 -0700 (PDT) From: Sun Jian To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org Cc: martin.lau@linux.dev, eddyz87@gmail.com, song@kernel.org, yonghong.song@linux.dev, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Sun Jian , syzbot+619b9ef527f510a57cfc@syzkaller.appspotmail.com Subject: [PATCH] selftests/bpf: Reject malformed IPv4/IPv6 skb test input Date: Sun, 29 Mar 2026 20:50:56 +0800 Message-ID: <20260329125056.1909087-1-sun.jian.kdev@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" bpf_prog_test_run_skb() derives skb->protocol from the Ethernet header through eth_type_trans(), but it does not verify that the provided linear input is long enough to contain the corresponding L3 base header. This can construct an inconsistent skb for test_run: the packet can be recognized as IPv6 while skb_headlen() still only covers ETH_HLEN bytes. In that case, helpers such as bpf_skb_adjust_room() may compute offsets based on the inferred protocol and operate on bytes beyond the initialized linear data, which can trigger KMSAN. Reject such malformed IPv4/IPv6 skb test input early by checking that the linear head covers both the Ethernet header and the corresponding IPv4/IPv6 base header before running the program. Reported-by: syzbot+619b9ef527f510a57cfc@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D619b9ef527f510a57cfc Signed-off-by: Sun Jian --- net/bpf/test_run.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 178c4738e63b..65cfb408f52b 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -1118,6 +1118,25 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, con= st union bpf_attr *kattr, skb->protocol =3D eth_type_trans(skb, dev); skb_reset_network_header(skb); =20 + switch (skb->protocol) { + case htons(ETH_P_IP): + if (skb_headlen(skb) < ETH_HLEN + sizeof(struct iphdr)) { + ret =3D -EINVAL; + goto out; + } + break; +#if IS_ENABLED(CONFIG_IPV6) + case htons(ETH_P_IPV6): + if (skb_headlen(skb) < ETH_HLEN + sizeof(struct ipv6hdr)) { + ret =3D -EINVAL; + goto out; + } + break; +#endif + default: + break; + } + switch (skb->protocol) { case htons(ETH_P_IP): sk->sk_family =3D AF_INET; base-commit: cbfffcca2bf0622b601b7eaf477aa29035169184 --=20 2.43.0