From 41af4459ac47e107093c3f54b6875d54723aa613 Mon Sep 17 00:00:00 2001

From: Sebastian Hasler <sebastian.hasler@stuvus.uni-stuttgart.de>

Date: Thu, 13 Jan 2022 16:32:49 +0100

Subject: [PATCH 2/2] virtiofsd: Do not support blocking flock

With the current implementation, blocking flock can lead to

deadlock. Thus, it's better to return EOPNOTSUPP if a user attempts

to perform a blocking flock request.

Signed-off-by: Sebastian Hasler <sebastian.hasler@stuvus.uni-stuttgart.de>

Message-Id: <20220113153249.710216-1-sebastian.hasler@stuvus.uni-stuttgart.de>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

Reviewed-by: Vivek Goyal <vgoyal@redhat.com>

Reviewed-by: Greg Kurz <groug@kaod.org>

---

 tools/virtiofsd/passthrough_ll.c | 9 +++++++++

 1 file changed, 9 insertions(+)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c

index b3d0674f6d..3e56d1cd95 100644

--- a/tools/virtiofsd/passthrough_ll.c

+++ b/tools/virtiofsd/passthrough_ll.c

@@ -2467,6 +2467,15 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,

     int res;

     (void)ino;

+    if (!(op & LOCK_NB)) {

+        /*

+         * Blocking flock can deadlock as there is only one thread

+         * serving the queue.

+         */

+        fuse_reply_err(req, EOPNOTSUPP);

+        return;

+    }

+

     res = flock(lo_fi_fd(req, fi), op);

     fuse_reply_err(req, res == -1 ? errno : 0);

-- 

2.35.1