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Tue, 23 Jun 2026 00:15:36 -0700 (PDT) X-Received: by 2002:a05:6a00:238c:b0:845:3d4b:8f8a with SMTP id d2e1a72fcca58-845508a1d4fmr20512970b3a.35.1782198936570; Tue, 23 Jun 2026 00:15:36 -0700 (PDT) Received: from [192.168.192.71] ([50.47.147.90]) by smtp.googlemail.com with ESMTPSA id d2e1a72fcca58-84564d8a7f0sm10037091b3a.13.2026.06.23.00.15.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Jun 2026 00:15:36 -0700 (PDT) Message-ID: <2ea3bc97-8422-4e33-88b8-a8b0fee79793@canonical.com> Date: Tue, 23 Jun 2026 00:15:35 -0700 Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] apparmor: mediate the implicit connect of TCP fast open sendmsg To: hexlabsecurity@proton.me, Ryan Lee Cc: Mickael Salaun , Stephen Smalley , James Morris , Matthieu Buffet , linux-security-module@vger.kernel.org, Mikhail Ivanov , "Serge E. Hallyn" , linux-kernel@vger.kernel.org, Paul Moore , apparmor@lists.ubuntu.com References: <20260622-b4-disp-aba401c6-v1-1-9d74343c7ced@proton.me> Content-Language: en-US From: John Johansen Autocrypt: addr=john.johansen@canonical.com; keydata= xsFNBE5mrPoBEADAk19PsgVgBKkImmR2isPQ6o7KJhTTKjJdwVbkWSnNn+o6Up5knKP1f49E BQlceWg1yp/NwbR8ad+eSEO/uma/K+PqWvBptKC9SWD97FG4uB4/caomLEU97sLQMtnvGWdx rxVRGM4anzWYMgzz5TZmIiVTZ43Ou5VpaS1Vz1ZSxP3h/xKNZr/TcW5WQai8u3PWVnbkjhSZ PHv1BghN69qxEPomrJBm1gmtx3ZiVmFXluwTmTgJOkpFol7nbJ0ilnYHrA7SX3CtR1upeUpM a/WIanVO96WdTjHHIa43fbhmQube4txS3FcQLOJVqQsx6lE9B7qAppm9hQ10qPWwdfPy/+0W 6AWtNu5ASiGVCInWzl2HBqYd/Zll93zUq+NIoCn8sDAM9iH+wtaGDcJywIGIn+edKNtK72AM gChTg/j1ZoWH6ZeWPjuUfubVzZto1FMoGJ/SF4MmdQG1iQNtf4sFZbEgXuy9cGi2bomF0zvy BJSANpxlKNBDYKzN6Kz09HUAkjlFMNgomL/cjqgABtAx59L+dVIZfaF281pIcUZzwvh5+JoG eOW5uBSMbE7L38nszooykIJ5XrAchkJxNfz7k+FnQeKEkNzEd2LWc3QF4BQZYRT6PHHga3Rg ykW5+1wTMqJILdmtaPbXrF3FvnV0LRPcv4xKx7B3fGm7ygdoowARAQABzStKb2huIEpvaGFu c2VuIDxqb2huLmpvaGFuc2VuQGNhbm9uaWNhbC5jb20+wsF3BBMBCgAhBQJOjRdaAhsDBQsJ CAcDBRUKCQgLBRYCAwEAAh4BAheAAAoJEAUvNnAY1cPYi0wP/2PJtzzt0zi4AeTrI0w3Rj8E Waa1NZWw4GGo6ehviLfwGsM7YLWFAI8JB7gsuzX/im16i9C3wHYXKs9WPCDuNlMc0rvivqUI JXHHfK7UHtT0+jhVORyyVVvX+qZa7HxdZw3jK+ROqUv4bGnImf31ll99clzo6HpOY59soa8y 66/lqtIgDckcUt/1ou9m0DWKwlSvulL1qmD25NQZSnvB9XRZPpPd4bea1RTa6nklXjznQvTm MdLq5aJ79j7J8k5uLKvE3/pmpbkaieEsGr+azNxXm8FPcENV7dG8Xpd0z06E+fX5jzXHnj69 DXXc3yIvAXsYZrXhnIhUA1kPQjQeNG9raT9GohFPMrK48fmmSVwodU8QUyY7MxP4U6jE2O9L 7v7AbYowNgSYc+vU8kFlJl4fMrX219qU8ymkXGL6zJgtqA3SYHskdDBjtytS44OHJyrrRhXP W1oTKC7di/bb8jUQIYe8ocbrBz3SjjcL96UcQJecSHu0qmUNykgL44KYzEoeFHjr5dxm+DDg OBvtxrzd5BHcIbz0u9ClbYssoQQEOPuFmGQtuSQ9FmbfDwljjhrDxW2DFZ2dIQwIvEsg42Hq 5nv/8NhW1whowliR5tpm0Z0KnQiBRlvbj9V29kJhs7rYeT/dWjWdfAdQSzfoP+/VtPRFkWLr 0uCwJw5zHiBgzsFNBE5mrPoBEACirDqSQGFbIzV++BqYBWN5nqcoR+dFZuQL3gvUSwku6ndZ vZfQAE04dKRtIPikC4La0oX8QYG3kI/tB1UpEZxDMB3pvZzUh3L1EvDrDiCL6ef93U+bWSRi GRKLnNZoiDSblFBST4SXzOR/m1wT/U3Rnk4rYmGPAW7ltfRrSXhwUZZVARyJUwMpG3EyMS2T dLEVqWbpl1DamnbzbZyWerjNn2Za7V3bBrGLP5vkhrjB4NhrufjVRFwERRskCCeJwmQm0JPD IjEhbYqdXI6uO+RDMgG9o/QV0/a+9mg8x2UIjM6UiQ8uDETQha55Nd4EmE2zTWlvxsuqZMgy W7gu8EQsD+96JqOPmzzLnjYf9oex8F/gxBSEfE78FlXuHTopJR8hpjs6ACAq4Y0HdSJohRLn 5r2CcQ5AsPEpHL9rtDW/1L42/H7uPyIfeORAmHFPpkGFkZHHSCQfdP4XSc0Obk1olSxqzCAm uoVmRQZ3YyubWqcrBeIC3xIhwQ12rfdHQoopELzReDCPwmffS9ctIb407UYfRQxwDEzDL+m+ TotTkkaNlHvcnlQtWEfgwtsOCAPeY9qIbz5+i1OslQ+qqGD2HJQQ+lgbuyq3vhefv34IRlyM sfPKXq8AUTZbSTGUu1C1RlQc7fpp8W/yoak7dmo++MFS5q1cXq29RALB/cfpcwARAQABwsFf BBgBCgAJBQJOZqz6AhsMAAoJEAUvNnAY1cPYP9cP/R10z/hqLVv5OXWPOcpqNfeQb4x4Rh4j h/jS9yjes4uudEYU5xvLJ9UXr0wp6mJ7g7CgjWNxNTQAN5ydtacM0emvRJzPEEyujduesuGy a+O6dNgi+ywFm0HhpUmO4sgs9SWeEWprt9tWrRlCNuJX+u3aMEQ12b2lslnoaOelghwBs8IJ r998vj9JBFJgdeiEaKJLjLmMFOYrmW197As7DTZ+R7Ef4gkWusYFcNKDqfZKDGef740Xfh9d yb2mJrDeYqwgKb7SF02Hhp8ZnohZXw8ba16ihUOnh1iKH77Ff9dLzMEJzU73DifOU/aArOWp JZuGJamJ9EkEVrha0B4lN1dh3fuP8EjhFZaGfLDtoA80aPffK0Yc1R/pGjb+O2Pi0XXL9AVe qMkb/AaOl21F9u1SOosciy98800mr/3nynvid0AKJ2VZIfOP46nboqlsWebA07SmyJSyeG8c XA87+8BuXdGxHn7RGj6G+zZwSZC6/2v9sOUJ+nOna3dwr6uHFSqKw7HwNl/PUGeRqgJEVu++ +T7sv9+iY+e0Y+SolyJgTxMYeRnDWE6S77g6gzYYHmcQOWP7ZMX+MtD4SKlf0+Q8li/F9GUL p0rw8op9f0p1+YAhyAd+dXWNKf7zIfZ2ME+0qKpbQnr1oizLHuJX/Telo8KMmHter28DPJ03 lT9Q Organization: Canonical In-Reply-To: <20260622-b4-disp-aba401c6-v1-1-9d74343c7ced@proton.me> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 6/22/26 13:57, Bryam Vargas via B4 Relay wrote: > From: Bryam Vargas > > sendmsg()/sendto() with MSG_FASTOPEN is a combination of connect(2) and > write(2): it opens the connection in the SYN. apparmor_socket_sendmsg() > only checks AA_MAY_SEND, so a profile that grants send but denies connect > lets a confined task open an outbound TCP/MPTCP connection that connect(2) > would have refused, bypassing connect mediation. > > Mediate the implicit connect when MSG_FASTOPEN is set and a destination > is supplied. Add it to apparmor_socket_sendmsg() (not the shared > aa_sock_msg_perm() helper, which recvmsg also uses) and call aa_sk_perm() > directly, mirroring the selinux and tomoyo fixes. sk_is_tcp() does not > cover MPTCP fast open, so the SOCK_STREAM/IPPROTO_MPTCP arm is explicit. > > Fixes: cf60af03ca4e ("net-tcp: Fast Open client - sendmsg(MSG_FASTOPEN)") > Cc: stable@vger.kernel.org > Signed-off-by: Bryam Vargas Acked-by: John Johansen I have pulled this into my tree > --- > This is the patch and reproducer requested in [1]. A userspace regression test > (tests/regression/apparmor/net_inet_tcp_fastopen) follows separately to the > apparmor tree, as suggested. > > Reproducer (behavioral; the bypassed value is policy, not bus state, so no special > hardware). Under a profile that grants inet/inet6 stream send but denies connect, on > the current Debian security kernel 6.12.94 (apparmor active): > > [TCP ] connect(2)=EACCES sendto(MSG_FASTOPEN)=OK -> connect bypassed (listener accepted) > [TCP6] connect(2)=EACCES sendto(MSG_FASTOPEN)=OK -> connect bypassed > > The kernel audit shows the connect(2) denial and no connect record for the fastopen > sendto: > > apparmor="DENIED" operation="connect" profile="egress_restricted" comm="lsm_tfo_ab" > family="inet" sock_type="stream" protocol=6 requested_mask="connect" denied_mask="connect" > > With this patch the fastopen sendto hits that same connect denial. Full reproducer > available on request. > > Same-class fixes: selinux [2], tomoyo [3]; the original cross-LSM report (landlock, > the first instance) is [4]. > > [1] https://lore.kernel.org/r/20260619011138.264578-1-hexlabsecurity@proton.me > [2] https://lore.kernel.org/r/20260618175513.112443-2-stephen.smalley.work@gmail.com > [3] https://lore.kernel.org/r/20260619002207.61104-1-matthieu@buffet.re > [4] https://lore.kernel.org/r/20260616201615.275032-1-hexlabsecurity@proton.me > --- > security/apparmor/lsm.c | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c > index 3491e9f60194..e01efdf50efa 100644 > --- a/security/apparmor/lsm.c > +++ b/security/apparmor/lsm.c > @@ -1422,7 +1422,21 @@ static int aa_sock_msg_perm(const char *op, u32 request, struct socket *sock, > static int apparmor_socket_sendmsg(struct socket *sock, > struct msghdr *msg, int size) > { > - return aa_sock_msg_perm(OP_SENDMSG, AA_MAY_SEND, sock, msg, size); > + int error = aa_sock_msg_perm(OP_SENDMSG, AA_MAY_SEND, sock, msg, size); > + > + if (error) > + return error; > + > + /* TCP fast open carries connect() semantics in sendmsg(); mediate > + * the implicit connect so it cannot bypass the connect permission. > + */ > + if ((msg->msg_flags & MSG_FASTOPEN) && msg->msg_name && > + (sk_is_tcp(sock->sk) || > + (sk_is_inet(sock->sk) && sock->sk->sk_type == SOCK_STREAM && > + sock->sk->sk_protocol == IPPROTO_MPTCP))) > + error = aa_sk_perm(OP_CONNECT, AA_MAY_CONNECT, sock->sk); > + > + return error; > } > > static int apparmor_socket_recvmsg(struct socket *sock, > > --- > base-commit: 4549871118cf616eecdd2d939f78e3b9e1dddc48 > change-id: 20260622-b4-disp-aba401c6-f02842c82975 > > Best regards,