[PATCH 5.15.y] xen-blkfront: unbind irq before tearing down ring and shadow requests

[Sasha Levin <sashal@kernel.org>]

From: Yuchao Zhang <ndaugoing@gmail.com>

[ Upstream commit f3e27b7955727a4d7c0e9264a2a209fbba788bdc ]

In blkif_free_ring(), the driver tears down the ring's persistent grants,
shadow request arrays, and shared ring structure (xenbus_teardown_ring),
and only calls unbind_from_irqhandler() at the very end.

While blkif_free_ring() is freeing persistent grants and clearing the
shadow array, the event channel interrupt (blkif_interrupt) is still
registered and active.  If an interrupt arrives from the backend during
this teardown window, blkif_interrupt() reads rinfo->ring.sring and,
via blkif_completion(), accesses rinfo->shadow[id].grants_used and
rinfo->shadow[id].sg.  blkif_free_ring() tears these structures down
without holding rinfo->ring_lock, and the handler only checks
info->connected at entry, so this is a real race resulting in a
use-after-free or NULL pointer dereference.

Fix this by moving unbind_from_irqhandler() to the beginning of
blkif_free_ring().  Calling unbind_from_irqhandler() first frees the
IRQ and synchronizes with any in-flight interrupt handlers on other CPUs
before ring memory and shadow request structures are deallocated,
matching the teardown order in drivers/net/xen-netfront.c.

Fixes: 11659569f720 ("xen/blkfront: split per device io_lock")
Cc: stable@vger.kernel.org
Signed-off-by: Yuchao Zhang <ndaugoing@gmail.com>
Acked-by: Roger Pau Monné <roger@xenproject.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20260922072155.34625-1-ndaugoing@gmail.com>
[ sashal: Adjusted context to preserve direct grant and memory cleanup where upstream uses xenbus_teardown_ring(). ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/block/xen-blkfront.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 831747ba8113c..02dc4a67ac82f 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1215,6 +1215,14 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 	struct blkfront_info *info = rinfo->dev_info;
 	int i, j, segs;
 
+	/*
+	 * Interrupt teardown must be done ahead of freeing queue-related
+	 * data, otherwise the interrupt handler can race with the cleanup.
+	 */
+	if (rinfo->irq)
+		unbind_from_irqhandler(rinfo->irq, rinfo);
+	rinfo->evtchn = rinfo->irq = 0;
+
 	/*
 	 * Remove indirect pages, this only happens when using indirect
 	 * descriptors but not persistent grants
@@ -1304,10 +1312,6 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 	free_pages_exact(rinfo->ring.sring,
 			 info->nr_ring_pages * XEN_PAGE_SIZE);
 	rinfo->ring.sring = NULL;
-
-	if (rinfo->irq)
-		unbind_from_irqhandler(rinfo->irq, rinfo);
-	rinfo->evtchn = rinfo->irq = 0;
 }
 
 static void blkif_free(struct blkfront_info *info, int suspend)
-- 
2.53.0