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[89.24.32.159]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-bc835430dd3sm73470066b.52.2026.05.07.05.06.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 May 2026 05:06:31 -0700 (PDT) Message-ID: Date: Thu, 7 May 2026 14:06:30 +0200 Precedence: bulk X-Mailing-List: netdev@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, echaudro@redhat.com, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, jbenc@redhat.com, e@erig.me, yi.y.yang@intel.com, yuantan098@gmail.com, yifanwucs@gmail.com, tomapufckgml@gmail.com, bird@lzu.edu.cn, ldy3087146292@gmail.com Subject: Re: [PATCH net 1/1] openvswitch: reject oversized NSH MD2 metadata in push_nsh To: Ren Wei , netdev@vger.kernel.org, dev@openvswitch.org References: <9d2b5c6127e149ebd35094d662bfd008c20347c2.1777120226.git.ldy3087146292@gmail.com> <9c1f6c24-3641-4bef-aad7-8f276def50a8@ovn.org> Content-Language: en-US From: Ilya Maximets Autocrypt: addr=i.maximets@ovn.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/25/26 10:19 PM, Ilya Maximets wrote: > On 4/25/26 6:40 PM, Ren Wei wrote: >> From: Douya Le >> >> The NSH header length is encoded in 4-byte words in a 6-bit field. >> The current push_nsh validation only checks the MD2 payload against >> NSH_CTX_HDRS_MAX_LEN, which still allows metadata sizes that cannot be >> represented once the base header is included. >> >> Reject MD2 metadata lengths whose total NSH header size cannot be >> encoded exactly in the NSH length field, whether because the field >> would wrap or because the length is not a multiple of 4 bytes. >> >> Fixes: b2d0f5d5dc53 ("openvswitch: enable NSH support") >> Cc: stable@kernel.org >> Reported-by: Yuan Tan >> Reported-by: Yifan Wu >> Reported-by: Juefei Pu >> Reported-by: Xin Liu >> Tested-by: Douya Le >> Signed-off-by: Douya Le >> Signed-off-by: Ren Wei >> --- >> net/openvswitch/flow_netlink.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c >> index 13052408a132..8a1ae5309c2c 100644 >> --- a/net/openvswitch/flow_netlink.c >> +++ b/net/openvswitch/flow_netlink.c >> @@ -1432,7 +1432,13 @@ static int nsh_key_put_from_nlattr(const struct nlattr *attr, >> >> has_md2 = true; >> mdlen = nla_len(a); >> - if (mdlen > NSH_CTX_HDRS_MAX_LEN || mdlen <= 0) { >> + /* The NSH length field stores the total header size >> + * in 4-byte words in 6 bits. Reject MD2 metadata >> + * lengths that cannot be encoded exactly or would >> + * make the length field wrap. >> + */ >> + if (mdlen <= 0 || !IS_ALIGNED(mdlen, 4) || >> + NSH_BASE_HDR_LEN + mdlen > (NSH_LEN_MASK << 2)) { >> OVS_NLERR( >> log, >> "Invalid MD length %d for MD type %d", > > I don't think the check is a problem here, the problem is that the constants > are not correct. We actually had them fixed in userspace, but looks like > no-one ported the change to the kernel side: > https://patchwork.ozlabs.org/project/openvswitch/patch/1540503710-23597-1-git-send-email-pkusunyifeng@gmail.com/ > > Adjusting the macros should solve the potential overflow issue. However, > even if the value overflows the 6-bit length, it will just be truncated to > a smaller value and nothing bad should happen in this case, as far as header > push is concerned. The context was wrong already, so pushing a truncated > context doesn't make it more wrong. But we should still fix the constants, > so the checks make sense, of course. I posted a fix for the macros here: https://lore.kernel.org/netdev/20260507120434.2962505-1-i.maximets@ovn.org/T/#u > > The same for alignment, if the user provides an invalid header that is not > multiple of 4, the code will just truncate it to the previous multiple of 4, > which should not be a problem, as it wasn't correct in the first place. We > could add this check just to warn the user that they are doing something wrong, > but not having it should not cause any real issues. > > Note, the userpace change linked above did fix the real issue in userspace, > but for the kernel side there seem to be no real memory related issues caused > by the wrong constants. > > Best regards, Ilya Maximets.