[PATCH 6.18.y 3/3] fuse: fix race between interrupt and resend

[Sasha Levin <sashal@kernel.org>]

From: Miklos Szeredi <mszeredi@redhat.com>

[ Upstream commit ed9c881f3b498383f73c42712b359419da42a7b0 ]

After commit f8fce75fedf7 ("fuse: clear intr_entry in fuse_resend and
fuse_remove_pending_req") the WARN_ON(!list_empty(&req->intr_entry)) in
fuse_request_free() still triggers due to the following race:

In request_wait_answer()
  if (test_bit(FR_SENT, &req->flags)) -> returns true

In fuse_chan_resend()
  clear_bit(FR_SENT, &req->flags)

In request_wait_answer()
  queue_interrupt(req)

Fix by:

 - move clearing FR_SENT inside fpq->lock

 - move setting FR_PENDING inside fiq->lock

 - recheck FR_SENT after acquiring fiq->lock in fuse_dev_queue_interrupt()

Reported-by: zdi-disclosures@trendmicro.com
Fixes: f8fce75fedf7 ("fuse: clear intr_entry in fuse_resend and fuse_remove_pending_req")
Cc: stable@vger.kernel.org # 6.9
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
[ adjusted context to use `fc->iq` in `fuse_resend()` since `struct fuse_chan` doesn't exist in this tree ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/fuse/dev.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 8a38a263295fe..8bbff1f19d6bd 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -353,7 +353,8 @@ void fuse_dev_queue_forget(struct fuse_iqueue *fiq,
 void fuse_dev_queue_interrupt(struct fuse_iqueue *fiq, struct fuse_req *req)
 {
 	spin_lock(&fiq->lock);
-	if (list_empty(&req->intr_entry)) {
+	/* Repeat FR_SENT test after obtaining the lock to prevent race with fuse_resend() */
+	if (list_empty(&req->intr_entry) && test_bit(FR_SENT, &req->flags)) {
 		list_add_tail(&req->intr_entry, &fiq->interrupts);
 		/*
 		 * Pairs with smp_mb() implied by test_and_set_bit()
@@ -2010,7 +2011,7 @@ static int fuse_notify_retrieve(struct fuse_conn *fc, unsigned int size,
 static void fuse_resend(struct fuse_conn *fc)
 {
 	struct fuse_dev *fud;
-	struct fuse_req *req, *next;
+	struct fuse_req *req;
 	struct fuse_iqueue *fiq = &fc->iq;
 	LIST_HEAD(to_queue);
 	unsigned int i;
@@ -2025,24 +2026,20 @@ static void fuse_resend(struct fuse_conn *fc)
 		struct fuse_pqueue *fpq = &fud->pq;
 
 		spin_lock(&fpq->lock);
-		for (i = 0; i < FUSE_PQ_HASH_SIZE; i++)
-			list_splice_tail_init(&fpq->processing[i], &to_queue);
+		for (i = 0; i < FUSE_PQ_HASH_SIZE; i++) {
+			struct list_head *this_queue = &fpq->processing[i];
+
+			list_for_each_entry(req, this_queue, list)
+				clear_bit(FR_SENT, &req->flags);
+			list_splice_tail_init(this_queue, &to_queue);
+		}
 		spin_unlock(&fpq->lock);
 	}
 	spin_unlock(&fc->lock);
 
-	list_for_each_entry_safe(req, next, &to_queue, list) {
-		set_bit(FR_PENDING, &req->flags);
-		clear_bit(FR_SENT, &req->flags);
-		/* mark the request as resend request */
-		req->in.h.unique |= FUSE_UNIQUE_RESEND;
-	}
-
 	spin_lock(&fiq->lock);
 	if (!fiq->connected) {
 		spin_unlock(&fiq->lock);
-		list_for_each_entry(req, &to_queue, list)
-			clear_bit(FR_PENDING, &req->flags);
 		fuse_dev_end_requests(&to_queue);
 		return;
 	}
@@ -2051,6 +2048,10 @@ static void fuse_resend(struct fuse_conn *fc)
 	 * intr_entry on fiq->interrupts after the request is re-queued.
 	 */
 	list_for_each_entry(req, &to_queue, list) {
+		set_bit(FR_PENDING, &req->flags);
+		/* mark the request as resend request */
+		req->in.h.unique |= FUSE_UNIQUE_RESEND;
+
 		if (test_bit(FR_INTERRUPTED, &req->flags))
 			list_del_init(&req->intr_entry);
 	}
-- 
2.53.0