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[2003:cf:5749:de00:7c66:abd9:5f8b:deba]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-64750a6ea36sm12307884a12.2.2025.12.01.04.24.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Dec 2025 04:24:22 -0800 (PST) From: Alexander Mikhalitsyn To: kees@kernel.org Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Andy Lutomirski , Will Drewry , Jonathan Corbet , Shuah Khan , Tycho Andersen , Andrei Vagin , Christian Brauner , =?UTF-8?q?St=C3=A9phane=20Graber?= , Alexander Mikhalitsyn Subject: [PATCH v1 4/6] seccomp: handle multiple listeners case Date: Mon, 1 Dec 2025 13:24:01 +0100 Message-ID: <20251201122406.105045-5-aleksandr.mikhalitsyn@canonical.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20251201122406.105045-1-aleksandr.mikhalitsyn@canonical.com> References: <20251201122406.105045-1-aleksandr.mikhalitsyn@canonical.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable If we have more than one listener in the tree and lower listener wants us to continue syscall (SECCOMP_USER_NOTIF_FLAG_CONTINUE) we must consult with upper listeners first, otherwise it is a clear seccomp restrictions bypass scenario. Cc: linux-kernel@vger.kernel.org Cc: bpf@vger.kernel.org Cc: Kees Cook Cc: Andy Lutomirski Cc: Will Drewry Cc: Jonathan Corbet Cc: Shuah Khan Cc: Tycho Andersen Cc: Andrei Vagin Cc: Christian Brauner Cc: St=C3=A9phane Graber Signed-off-by: Alexander Mikhalitsyn Reviewed-by: Tycho Andersen (AMD) --- kernel/seccomp.c | 16 ++++++++++++++-- 1 file changed, 14 insertions(+), 2 deletions(-) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index ded3f6a6430b..ad733f849e0f 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -450,6 +450,9 @@ static u32 seccomp_run_filters(const struct seccomp_dat= a *sd, ret =3D cur_ret; matches->n =3D 1; matches->filters[0] =3D f; + } else if ((ACTION_ONLY(cur_ret) =3D=3D ACTION_ONLY(ret)) && + ACTION_ONLY(cur_ret) =3D=3D SECCOMP_RET_USER_NOTIF) { + matches->filters[matches->n++] =3D f; } } return ret; @@ -1362,8 +1365,17 @@ static int __seccomp_filter(int this_syscall, const = bool recheck_after_trace) return 0; =20 case SECCOMP_RET_USER_NOTIF: - if (seccomp_do_user_notification(match, &sd)) - goto skip; + for (unsigned char i =3D 0; i < matches.n; i++) { + match =3D matches.filters[i]; + /* + * If userspace wants us to skip this syscall, do so. + * But if userspace wants to continue syscall, we + * must consult with the upper-level filters listeners + * and act accordingly. + */ + if (seccomp_do_user_notification(match, &sd)) + goto skip; + } =20 return 0; =20 --=20 2.43.0