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[78.80.108.129]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4957bff4784sm46669205e9.4.2026.07.24.05.34.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Jul 2026 05:34:56 -0700 (PDT) Message-ID: Date: Fri, 24 Jul 2026 14:34:54 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: i.maximets@ovn.org, aconole@redhat.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, dev@openvswitch.org, linux-kernel@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, tgopinath@linux.microsoft.com, kys@microsoft.com Subject: Re: [PATCH net v3] net/openvswitch: check Ethernet header length in key_extract() To: Eelco Chaudron , "Cen Zhang (Microsoft)" References: <20260723233757.96356-1-blbllhy@gmail.com> <8082BACD-66E4-4C6C-ADA6-92231F1ECF39@redhat.com> Content-Language: en-US From: Ilya Maximets Autocrypt: addr=i.maximets@ovn.org; keydata= xsFNBF77bOMBEADVZQ4iajIECGfH3hpQMQjhIQlyKX4hIB3OccKl5XvB/JqVPJWuZQRuqNQG /B70MP6km95KnWLZ4H1/5YOJK2l7VN7nO+tyF+I+srcKq8Ai6S3vyiP9zPCrZkYvhqChNOCF pNqdWBEmTvLZeVPmfdrjmzCLXVLi5De9HpIZQFg/Ztgj1AZENNQjYjtDdObMHuJQNJ6ubPIW cvOOn4WBr8NsP4a2OuHSTdVyAJwcDhu+WrS/Bj3KlQXIdPv3Zm5x9u/56NmCn1tSkLrEgi0i /nJNeH5QhPdYGtNzPixKgPmCKz54/LDxU61AmBvyRve+U80ukS+5vWk8zvnCGvL0ms7kx5sA tETpbKEV3d7CB3sQEym8B8gl0Ux9KzGp5lbhxxO995KWzZWWokVUcevGBKsAx4a/C0wTVOpP FbQsq6xEpTKBZwlCpxyJi3/PbZQJ95T8Uw6tlJkPmNx8CasiqNy2872gD1nN/WOP8m+cIQNu o6NOiz6VzNcowhEihE8Nkw9V+zfCxC8SzSBuYCiVX6FpgKzY/Tx+v2uO4f/8FoZj2trzXdLk BaIiyqnE0mtmTQE8jRa29qdh+s5DNArYAchJdeKuLQYnxy+9U1SMMzJoNUX5uRy6/3KrMoC/ 7zhn44x77gSoe7XVM6mr/mK+ViVB7v9JfqlZuiHDkJnS3yxKPwARAQABzSJJbHlhIE1heGlt ZXRzIDxpLm1heGltZXRzQG92bi5vcmc+wsGUBBMBCAA+AhsDBQsJCAcCBhUKCQgLAgQWAgMB Ah4BAheAFiEEh+ma1RKWrHCY821auffsd8gpv5YFAmfB9JAFCQyI7q0ACgkQuffsd8gpv5YQ og/8DXt1UOznvjdXRHVydbU6Ws+1iUrxlwnFH4WckoFgH4jAabt25yTa1Z4YX8Vz0mbRhTPX M/j1uORyObLem3of4YCd4ymh7nSu++KdKnNsZVHxMcoiic9ILPIaWYa8kTvyIDT2AEVfn9M+ vskM0yDbKa6TAHgr/0jCxbS+mvN0ZzDuR/LHTgy3e58097SWJohj0h3Dpu+XfuNiZCLCZ1/G AbBCPMw+r7baH/0evkX33RCBZwvh6tKu+rCatVGk72qRYNLCwF0YcGuNBsJiN9Aa/7ipkrA7 Xp7YvY3Y1OrKnQfdjp3mSXmknqPtwqnWzXvdfkWkZKShu0xSk+AjdFWCV3NOzQaH3CJ67NXm aPjJCIykoTOoQ7eEP6+m3WcgpRVkn9bGK9ng03MLSymTPmdINhC5pjOqBP7hLqYi89GN0MIT Ly2zD4m/8T8wPV9yo7GRk4kkwD0yN05PV2IzJECdOXSSStsf5JWObTwzhKyXJxQE+Kb67Wwa LYJgltFjpByF5GEO4Xe7iYTjwEoSSOfaR0kokUVM9pxIkZlzG1mwiytPadBt+VcmPQWcO5pi WxUI7biRYt4aLriuKeRpk94ai9+52KAk7Lz3KUWoyRwdZINqkI/aDZL6meWmcrOJWCUMW73e 4cMqK5XFnGqolhK4RQu+8IHkSXtmWui7LUeEvO/OwU0EXvts4wEQANCXyDOic0j2QKeyj/ga OD1oKl44JQfOgcyLVDZGYyEnyl6b/tV1mNb57y/YQYr33fwMS1hMj9eqY6tlMTNz+ciGZZWV YkPNHA+aFuPTzCLrapLiz829M5LctB2448bsgxFq0TPrr5KYx6AkuWzOVq/X5wYEM6djbWLc VWgJ3o0QBOI4/uB89xTf7mgcIcbwEf6yb/86Cs+jaHcUtJcLsVuzW5RVMVf9F+Sf/b98Lzrr 2/mIB7clOXZJSgtV79Alxym4H0cEZabwiXnigjjsLsp4ojhGgakgCwftLkhAnQT3oBLH/6ix 87ahawG3qlyIB8ZZKHsvTxbWte6c6xE5dmmLIDN44SajAdmjt1i7SbAwFIFjuFJGpsnfdQv1 OiIVzJ44kdRJG8kQWPPua/k+AtwJt/gjCxv5p8sKVXTNtIP/sd3EMs2xwbF8McebLE9JCDQ1 RXVHceAmPWVCq3WrFuX9dSlgf3RWTqNiWZC0a8Hn6fNDp26TzLbdo9mnxbU4I/3BbcAJZI9p 9ELaE9rw3LU8esKqRIfaZqPtrdm1C+e5gZa2gkmEzG+WEsS0MKtJyOFnuglGl1ZBxR1uFvbU VXhewCNoviXxkkPk/DanIgYB1nUtkPC+BHkJJYCyf9Kfl33s/bai34aaxkGXqpKv+CInARg3 fCikcHzYYWKaXS6HABEBAAHCwXwEGAEIACYCGwwWIQSH6ZrVEpascJjzbVq59+x3yCm/lgUC Z8H0qQUJDIjuxgAKCRC59+x3yCm/loAdD/wJCOhPp9711J18B9c4f+eNAk5vrC9Cj3RyOusH Hebb9HtSFm155Zz3xiizw70MSyOVikjbTocFAJo5VhkyuN0QJIP678SWzriwym+EG0B5P97h FSLBlRsTi4KD8f1Ll3OT03lD3o/5Qt37zFgD4mCD6OxAShPxhI3gkVHBuA0GxF01MadJEjMu jWgZoj75rCLG9sC6L4r28GEGqUFlTKjseYehLw0s3iR53LxS7HfJVHcFBX3rUcKFJBhuO6Ha /GggRvTbn3PXxR5UIgiBMjUlqxzYH4fe7pYR7z1m4nQcaFWW+JhY/BYHJyMGLfnqTn1FsIwP dbhEjYbFnJE9Vzvf+RJcRQVyLDn/TfWbETf0bLGHeF2GUPvNXYEu7oKddvnUvJK5U/BuwQXy TRFbae4Ie96QMcPBL9ZLX8M2K4XUydZBeHw+9lP1J6NJrQiX7MzexpkKNy4ukDzPrRE/ruui yWOKeCw9bCZX4a/uFw77TZMEq3upjeq21oi6NMTwvvWWMYuEKNi0340yZRrBdcDhbXkl9x/o skB2IbnvSB8iikbPng1ihCTXpA2yxioUQ96Akb+WEGopPWzlxTTK+T03G2ljOtspjZXKuywV Wu/eHyqHMyTu8UVcMRR44ki8wam0LMs+fH4dRxw5ck69AkV+JsYQVfI7tdOu7+r465LUfg== In-Reply-To: <8082BACD-66E4-4C6C-ADA6-92231F1ECF39@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/24/26 12:12 PM, Eelco Chaudron wrote: > > > On 24 Jul 2026, at 1:37, Cen Zhang (Microsoft) wrote: > >> When a packet arrives on an ARPHRD_NONE device (e.g. TUN), >> ovs_flow_key_extract() trusts the user-provided skb->protocol field: if >> it is ETH_P_TEB, the packet is classified as MAC_PROTO_ETHERNET and >> key_extract() is called without ensuring the skb has ETH_HLEN (14) bytes >> of linear data. key_extract() unconditionally pulls 2 * ETH_ALEN bytes >> for MAC addresses and parse_ethertype() pulls 2 more, either of which >> triggers a kernel BUG in __skb_pull() when the linear area is too small. >> >> kernel BUG at include/linux/skbuff.h:2848! >> RIP: 0010:key_extract+0xa7e/0xd90 net/openvswitch/flow.c:933 >> ovs_flow_key_extract+0x419/0xa70 >> ovs_vport_receive+0x222/0x390 >> netdev_frame_hook+0x3e0/0x630 >> tun_get_user+0x2d0c/0x38e0 >> >> Fixed by adding checks in key_extract() before pulling the Ethernet >> header. >> >> Fixes: 217ac77a3c25 ("openvswitch: allow L3 netdev ports") >> Reported-by: AutonomousCodeSecurity@microsoft.com >> Signed-off-by: Cen Zhang (Microsoft) > > Hi Cen, > > Thanks for the new revision. > > The doc comment for key_extract() also needs updating. It currently > states: > > * The caller must ensure that skb->len >= ETH_HLEN. > > The comment should be removed or replaced with a note that the > function returns -EINVAL when the frame is too short to contain an > Ethernet header. > > One more comment below. > > Cheers, > > Eelco > >> --- >> v3: Use check_header() per review, fix format issue. >> v2: Moved the check into key_extract() per Ilya Maximets. >> Link: https://lore.kernel.org/all/20260721143602.64677-1-blbllhy@gmail.com >> >> net/openvswitch/flow.c | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c >> index 66366982f604..fc4002353e17 100644 >> --- a/net/openvswitch/flow.c >> +++ b/net/openvswitch/flow.c >> @@ -911,6 +911,7 @@ static int key_extract_l3l4(struct sk_buff *skb, struct sw_flow_key *key) >> static int key_extract(struct sk_buff *skb, struct sw_flow_key *key) >> { >> struct ethhdr *eth; >> + int err; > > Since err is only used in the else block, it should be scoped there: > > } else { > int err = check_header(skb, ETH_HLEN); > > if (unlikely(err)) > return err; The 'eth' is also only used in the 'else' block, but defined at the top. It doesn't matter where, but I think, we should keep them together. > >> >> /* Flags are always used as part of stats */ >> key->tp.flags = 0; >> @@ -926,6 +927,10 @@ static int key_extract(struct sk_buff *skb, struct sw_flow_key *key) >> skb_reset_network_header(skb); >> key->eth.type = skb->protocol; >> } else { >> + err = check_header(skb, ETH_HLEN); >> + if (unlikely(err)) >> + return err; >> + >> eth = eth_hdr(skb); >> ether_addr_copy(key->eth.src, eth->h_source); >> ether_addr_copy(key->eth.dst, eth->h_dest); >> -- >> 2.53.0 >