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[34.83.123.78]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cc72aecaa7fsm1613635a12.21.2026.09.19.21.16.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 21:16:30 -0700 (PDT) From: Hui Peng To: Kees Cook , Andy Lutomirski , Will Drewry Cc: Bradley Morgan , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, Hui Peng Subject: [PATCH v2] seccomp: restore knotif->state when SECCOMP_ADDFD_FLAG_SEND is interrupted Date: Sun, 20 Sep 2026 04:16:29 +0000 Message-ID: <20260920041629.2453290-1-benquike@gmail.com> X-Mailer: git-send-email 2.55.0.1082.g2b9226bbc0-goog In-Reply-To: <202609192050.D1E0CD96@keescook> References: <20260919203514.2580997-1-benquike@gmail.com> <202609192050.D1E0CD96@keescook> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit In seccomp_notify_addfd(), when SECCOMP_ADDFD_FLAG_SEND is set, knotif->state is transitioned from SECCOMP_NOTIFY_SENT to SECCOMP_NOTIFY_REPLIED before dropping filter->notify_lock and waiting in wait_for_completion_interruptible(&kaddfd.completion). If wait_for_completion_interruptible() is interrupted by a signal before the target task processes the kaddfd entry, seccomp_notify_addfd() removes kaddfd.list from knotif->addfd via list_del(&kaddfd.list), but leaves knotif->state set to SECCOMP_NOTIFY_REPLIED. As a consequence: 1. When the target task wakes in seccomp_do_user_notification(), it observes knotif->state == SECCOMP_NOTIFY_REPLIED with an empty addfd list and zeroed knotif->val / knotif->error / knotif->flags, causing the supervised syscall to prematurely complete with return value 0 without installing the file descriptor. 2. Any subsequent retry of SECCOMP_IOCTL_NOTIF_SEND or SECCOMP_IOCTL_NOTIF_ADDFD by the supervisor fails with -EINPROGRESS (or -ENOENT after the target exits) because knotif->state is no longer SECCOMP_NOTIFY_SENT. Restore knotif->state = SECCOMP_NOTIFY_SENT when removing an unhandled SECCOMP_ADDFD_FLAG_SEND request from knotif->addfd, and add a kselftest (user_notification_addfd_send_interrupted) to cover this race. Fixes: 7cf97b125455 ("seccomp: Introduce addfd ioctl to seccomp user notifier") Reviewed-by: Bradley Morgan Assisted-by: LLM Signed-off-by: Hui Peng --- Changes in v2: - Added kselftest regression test (user_notification_addfd_send_interrupted) in tools/testing/selftests/seccomp/seccomp_bpf.c per Kees Cook. - Collected Reviewed-by tag from Bradley Morgan. kernel/seccomp.c | 7 +- tools/testing/selftests/seccomp/seccomp_bpf.c | 98 +++++++++++++++++++ 2 files changed, 103 insertions(+), 2 deletions(-) diff --git a/kernel/seccomp.c b/kernel/seccomp.c index 86cf4460d69e..94c7ba80a8f7 100644 --- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -1808,10 +1808,13 @@ static long seccomp_notify_addfd(struct seccomp_filter *filter, * We need to check again if the addfd request has been handled, * and if not, we will remove it from the queue. */ - if (list_empty(&kaddfd.list)) + if (list_empty(&kaddfd.list)) { ret = kaddfd.ret; - else + } else { list_del(&kaddfd.list); + if (addfd.flags & SECCOMP_ADDFD_FLAG_SEND) + knotif->state = SECCOMP_NOTIFY_SENT; + } out_unlock: mutex_unlock(&filter->notify_lock); -- 2.47.3