linux-kernel - [patch V3 34/51] posix-timers: Make signal overrun accounting sensible

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20240610164027.606874728@linutronix.de>
Date: Mon, 10 Jun 2024 18:42:47 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>,
 John Stultz <jstultz@...gle.com>,
 Peter Zijlstra <peterz@...radead.org>,
 Ingo Molnar <mingo@...nel.org>,
 Stephen Boyd <sboyd@...nel.org>,
 Eric Biederman <ebiederm@...ssion.com>,
 Oleg Nesterov <oleg@...hat.com>
Subject: [patch V3 34/51] posix-timers: Make signal overrun accounting
 sensible

The handling of the timer overrun in the signal code is inconsistent as it
takes previous overruns into account. This is just wrong as after the
reprogramming of a timer the overrun count starts over from a clean state,
i.e. 0.

Make the accounting in send_sigqueue() consistent with that.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/signal.c |   34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -1965,6 +1965,34 @@ int send_sigqueue(struct sigqueue *q, st
 	 */
 	q->info.si_sys_private = si_private;
 
+	/*
+	 * Set the overrun count to zero unconditionally. The posix timer
+	 * code does not self rearm periodic timers. They are rearmed from
+	 * dequeue_signal().
+	 *
+	 * But there is a situation where @q is already enqueued:
+	 *
+	 * 1) timer_settime()
+	 *      arm_timer()
+	 * 2) timer_expires()
+	 *      send_sigqueue(@q)
+	 *        enqueue(@q)
+	 * 3) timer_settime()
+	 *      arm_timer()
+	 * 4) timer_expires()
+	 *      send_sigqueue(@q) <- Observes @q already queued
+	 *
+	 * In this case incrementing si_overrun does not make sense because
+	 * there is no relationship between timer_settime() #1 and #2.
+	 *
+	 * The POSIX specification is useful as always: "The effect of
+	 * disarming or resetting a timer with pending expiration
+	 * notifications is unspecified."
+	 *
+	 * Just do the sensible thing and reset the overrun.
+	 */
+	q->info.si_overrun = 0;
+
 	ret = 1; /* the signal is ignored */
 	result = TRACE_SIGNAL_IGNORED;
 	if (!prepare_signal(sig, t, false))
@@ -1972,15 +2000,9 @@ int send_sigqueue(struct sigqueue *q, st
 
 	ret = 0;
 	if (unlikely(!list_empty(&q->list))) {
-		/*
-		 * If an SI_TIMER entry is already queue just increment
-		 * the overrun count.
-		 */
-		q->info.si_overrun++;
 		result = TRACE_SIGNAL_ALREADY_PENDING;
 		goto out;
 	}
-	q->info.si_overrun = 0;
 
 	signalfd_notify(t, sig);
 	pending = (type != PIDTYPE_PID) ? &t->signal->shared_pending : &t->pending;