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Fri, 29 May 2026 18:37:51 -0700 (PDT) From: AnonymeMeow To: amir73il@gmail.com Cc: brauner@kernel.org, jack@suse.cz, repnop@google.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, AnonymeMeow Subject: [PATCH v3 2/2] fanotify: allow reporting pidfds for reaped tasks Date: Sat, 30 May 2026 09:37:32 +0800 Message-ID: <20260530013732.50811-3-anonymemeow@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260530013732.50811-1-anonymemeow@gmail.com> References: <20260530013732.50811-1-anonymemeow@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Fanotify used to refuse to report pidfds for reaped tasks by applying a pid_has_task() check before calling pidfd_prepare(). This prevented userspace from obtaining information about the task. Fanotify events already hold a reference to the task's pid struct, so the check can be safely dropped and pidfds can be reported for reaped tasks as well. Signed-off-by: AnonymeMeow --- fs/notify/fanotify/fanotify_user.c | 18 +++++------------- 1 file changed, 5 insertions(+), 13 deletions(-) diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c index ebdd48942029..b604e3da58ad 100644 --- a/fs/notify/fanotify/fanotify_user.c +++ b/fs/notify/fanotify/fanotify_user.c @@ -904,20 +904,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, metadata.fd = fd >= 0 ? fd : FAN_NOFD; if (pidfd_mode) { - unsigned int tid_mode = FAN_GROUP_FLAG(group, FAN_REPORT_TID); - enum pid_type pidtype = tid_mode ? PIDTYPE_PID : PIDTYPE_TGID; - unsigned int pidfd_flags = tid_mode ? PIDFD_THREAD : 0; + unsigned int pidfd_flags = PIDFD_STALE; - /* - * The pid_has_task() check for an event->pid is performed - * preemptively in an attempt to catch out cases where the event - * listener reads events after the event generating task has - * already terminated. Depending on flag FAN_REPORT_FD_ERROR, - * report either -ESRCH or FAN_NOPIDFD to the event listener in - * those cases with all other pidfd creation errors reported as - * the error code itself or as FAN_EPIDFD. - */ - if (metadata.pid && pid_has_task(event->pid, pidtype)) + if (FAN_GROUP_FLAG(group, FAN_REPORT_TID)) + pidfd_flags |= PIDFD_THREAD; + + if (metadata.pid) pidfd = pidfd_prepare(event->pid, pidfd_flags, &pidfd_file); if (!FAN_GROUP_FLAG(group, FAN_REPORT_FD_ERROR) && pidfd < 0) -- 2.54.0