[PATCH 2/2] fs/fuse: fix potential memory leak from fuse_uring_cancel

[Bernd Schubert <bschubert@ddn.com>]

From: Jian Huang Li <ali@ddn.com>

This issue could be observed sometimes during libfuse xfstests, from
dmseg prints some like "kernel: WARNING: CPU: 4 PID: 0 at
fs/fuse/dev_uring.c:204 fuse_uring_destruct+0x1f5/0x200 [fuse]".

The cause is, if when fuse daemon just submitted
FUSE_IO_URING_CMD_REGISTER SQEs, then umount or fuse daemon quits at
this very early stage. After all uring queues stopped, might have one or
more unprocessed FUSE_IO_URING_CMD_REGISTER SQEs get processed then some
new ring entities are created and added to ent_avail_queue, and
immediately fuse_uring_cancel moved them to ent_in_userspace after SQEs
get canceled. These ring entities were not moved to ent_released, and
stayed in ent_in_userspace when fuse_uring_destruct was called.

One way to solve it would be to also free 'ent_in_userspace' in
fuse_uring_destruct(), but from code point of view it is hard to see why
it is needed. As suggested by Joanne, another solution is to avoid moving
entries in fuse_uring_cancel() to the 'ent_in_userspace' list and just
releasing them directly.

Fixes: b6236c8407cb ("fuse: {io-uring} Prevent mount point hang on fuse-server termination")
Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: <stable@vger.kernel.org> # v6.14
Signed-off-by: Jian Huang Li <ali@ddn.com>
Signed-off-by: Bernd Schubert <bschubert@ddn.com>
---
 fs/fuse/dev_uring.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index e7c1095b83b11fe46080c24f539df17e70969e21..d88a0c05434a04668241f09f123d5e3a9cc1621d 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -324,7 +324,7 @@ static void fuse_uring_stop_fuse_req_end(struct fuse_req *req)
 /*
  * Release a request/entry on connection tear down
  */
-static void fuse_uring_entry_teardown(struct fuse_ring_ent *ent)
+static void fuse_uring_entry_teardown(struct fuse_ring_ent *ent, int issue_flags)
 {
 	struct fuse_req *req;
 	struct io_uring_cmd *cmd;
@@ -352,7 +352,7 @@ static void fuse_uring_entry_teardown(struct fuse_ring_ent *ent)
 	spin_unlock(&queue->lock);
 
 	if (cmd)
-		io_uring_cmd_done(cmd, -ENOTCONN, IO_URING_F_UNLOCKED);
+		io_uring_cmd_done(cmd, -ENOTCONN, issue_flags);
 
 	if (req)
 		fuse_uring_stop_fuse_req_end(req);
@@ -383,7 +383,7 @@ static void fuse_uring_stop_list_entries(struct list_head *head,
 
 	/* no queue lock to avoid lock order issues */
 	list_for_each_entry_safe(ent, next, &to_teardown, list)
-		fuse_uring_entry_teardown(ent);
+		fuse_uring_entry_teardown(ent, IO_URING_F_UNLOCKED);
 }
 
 static void fuse_uring_teardown_entries(struct fuse_ring_queue *queue)
@@ -499,7 +499,7 @@ static void fuse_uring_cancel(struct io_uring_cmd *cmd,
 {
 	struct fuse_ring_ent *ent = uring_cmd_to_ring_ent(cmd);
 	struct fuse_ring_queue *queue;
-	bool need_cmd_done = false;
+	bool teardown = false;
 
 	/*
 	 * direct access on ent - it must not be destructed as long as
@@ -508,17 +508,14 @@ static void fuse_uring_cancel(struct io_uring_cmd *cmd,
 	queue = ent->queue;
 	spin_lock(&queue->lock);
 	if (ent->state == FRRS_AVAILABLE) {
-		ent->state = FRRS_USERSPACE;
-		list_move_tail(&ent->list, &queue->ent_in_userspace);
-		need_cmd_done = true;
-		ent->cmd = NULL;
+		ent->state = FRRS_TEARDOWN;
+		list_del_init(&ent->list);
+		teardown = true;
 	}
 	spin_unlock(&queue->lock);
 
-	if (need_cmd_done) {
-		/* no queue lock to avoid lock order issues */
-		io_uring_cmd_done(cmd, -ENOTCONN, issue_flags);
-	}
+	if (teardown)
+		fuse_uring_entry_teardown(ent, issue_flags);
 }
 
 static void fuse_uring_prepare_cancel(struct io_uring_cmd *cmd, int issue_flags,

-- 
2.43.0