[PATCH v2] erofs-utils: fix thread join loop in erofs_destroy_workqueue

[Nithurshen <nithurshen.dev@gmail.com>]

Currently, `erofs_destroy_workqueue` returns immediately if a single
`pthread_join` fails. This halts the teardown process, potentially
leaving orphanedd threads and leaking the workqueue's mutexes and
worker array.

Refactor the joining logic to unconditionally join all worker
threads. If a thread fails to join, print an error message with
the return code. Crucially, if any join fails, skip cleaning up
the synchronization primitives and worker array to prevent a severe
UAF vulnerability caused by still-living threads.

Signed-off-by: Nithurshen <nithurshen.dev@gmail.com>
---
 lib/workqueue.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/lib/workqueue.c b/lib/workqueue.c
index 18ee0f9..98c181b 100644
--- a/lib/workqueue.c
+++ b/lib/workqueue.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0+ OR Apache-2.0
 #include <pthread.h>
 #include <stdlib.h>
+#include "erofs/print.h"
 #include "erofs/workqueue.h"
 
 static void *worker_thread(void *arg)
@@ -42,6 +43,8 @@ static void *worker_thread(void *arg)
 
 int erofs_destroy_workqueue(struct erofs_workqueue *wq)
 {
+	int err = 0;
+
 	if (!wq)
 		return -EINVAL;
 
@@ -51,12 +54,20 @@ int erofs_destroy_workqueue(struct erofs_workqueue *wq)
 	pthread_mutex_unlock(&wq->lock);
 
 	while (wq->nworker) {
-		int ret = -pthread_join(wq->workers[wq->nworker - 1], NULL);
+		int ret = pthread_join(wq->workers[wq->nworker - 1], NULL);
 
-		if (ret)
-			return ret;
+		if (ret) {
+			erofs_err("failed to join worker thread %u: %d",
+				  wq->nworker - 1, ret);
+			if (!err)
+				err = -ret;
+		}
 		--wq->nworker;
 	}
+
+	if (err)
+		return err;
+
 	free(wq->workers);
 	pthread_mutex_destroy(&wq->lock);
 	pthread_cond_destroy(&wq->cond_empty);
-- 
2.43.0