From 603a0c40d414ea12509fc45f2b930449a8d4aad2 Mon Sep 17 00:00:00 2001 From: Yu Zhang Date: Mon, 26 Oct 2026 20:05:35 +1000 Subject: [PATCH] ptp: fix use-after-free in extts_fifo_show() reading tsevqs unlocked extts_fifo_show() walks ptp->tsevqs with list_count_nodes() and then list_first_entry() without holding ptp->tsevqs_lock, the spinlock that "protects tsevqs from concurrent access". Every other accessor of the list honours it: ptp_open() (list_add_tail), ptp_release() (list_del followed by kfree of the per-fd queue), ptp_clock_release() and ptp_clock_event() all take tsevqs_lock. extts_fifo_show() is the only one that does not. A per-fd timestamp queue is appended to tsevqs on open("/dev/ptpN") and removed and freed on close(), both under tsevqs_lock: scoped_guard(spinlock_irq, &ptp->tsevqs_lock) list_del(&queue->qlist); bitmap_free(queue->mask); kfree(queue); So a read of /sys/class/ptp/ptpN/fifo running concurrently with a close() of a /dev/ptpN fd can have list_count_nodes() walk into the queue that close() is removing and freeing, dereferencing freed memory (use-after-free) or a poisoned list pointer. Take tsevqs_lock around the list walk. The fifo only ever draws from the first queue, which is the registration-time queue created in ptp_clock_register() and freed only in ptp_clock_release(); that cannot run while the sysfs attribute is being read, so the dequeue from queue->buf under queue->lock may stay outside tsevqs_lock and the lock order is unchanged. Fixes: d26ab5a35ad9 ("ptp: Replace timestamp event queue with linked list") Cc: stable@vger.kernel.org Signed-off-by: Yu Zhang Link: https://patch.msgid.link/20261026100535.68114-1-yuz08559@gmail.com Signed-off-by: Jakub Kicinski --- drivers/ptp/ptp_sysfs.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/ptp/ptp_sysfs.c b/drivers/ptp/ptp_sysfs.c index dc398c6b7528..7d09256aca72 100644 --- a/drivers/ptp/ptp_sysfs.c +++ b/drivers/ptp/ptp_sysfs.c @@ -80,13 +80,17 @@ static ssize_t extts_fifo_show(struct device *dev, size_t qcnt; int cnt = 0; + spin_lock_irqsave(&ptp->tsevqs_lock, flags); cnt = list_count_nodes(&ptp->tsevqs); - if (cnt <= 0) + if (cnt <= 0) { + spin_unlock_irqrestore(&ptp->tsevqs_lock, flags); goto out; + } /* The sysfs fifo will always draw from the fist queue */ queue = list_first_entry(&ptp->tsevqs, struct timestamp_event_queue, qlist); + spin_unlock_irqrestore(&ptp->tsevqs_lock, flags); memset(&event, 0, sizeof(event)); spin_lock_irqsave(&queue->lock, flags);