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charset="utf-8" Content-Transfer-Encoding: quoted-printable On Sat, 07 Nov 2026 22:47:33 +0000, J=C3=A9r=C3=A9my Jean wrote: > tcp_inbound_hash() parses both TCP-MD5 and TCP-AO options when at > least one of the two features is enabled. With TCP_MD5SIG=3Dy and > TCP_AO=3Dn, a packet carrying an AO option reaches the disabled > tcp_inbound_ao_hash() stub. That stub returns success, so sockets > configured to require MD5 authentication end up accepting > unauthenticated data. A forged AO option skips the unsigned fast > path, which is the only place where tcp_inbound_hash() can return > SKB_DROP_REASON_TCP_MD5NOTFOUND. >=20 > The inverse configuration with TCP_MD5SIG=3Dn and TCP_AO=3Dy has the same > problem for an MD5 option on AO sockets. >=20 > Note that TCP-AO depends on 64BIT: therefore, every 32-bit kernel with > TCP_MD5SIG=3Dy is in the vulnerable configuration. >=20 > Make the disabled stubs reject options for the unsupported > authentication scheme. This matches the real helpers' behavior for > sockets without keys. It also means that kernels with TCP_MD5SIG=3Dn and > TCP_AO=3Dy now drop segments carrying an MD5 option on unkeyed sockets, > as kernels configured with TCP_MD5SIG=3Dy already do. >=20 > Fixes: 0a3a809089eb ("net/tcp: Verify inbound TCP-AO signed segments") > Cc: stable@vger.kernel.org > Signed-off-by: J=C3=A9r=C3=A9my Jean Reviewed-by: Kuniyuki Iwashima