vnc: Fixes for unix socket error handling

Minor fixes for unix socket error handling, see patches for details

v3:
Scoop up the v2 of patch 3
Fix checkpatch warnings

Cole Robinson (3):
vnc: Don't assert if opening unix socket fails
vnc: Tweak error when init fails
qemu-sockets: Report explicit error if unlink fails

 ui/vnc.c            | 6 ++++--
 util/qemu-sockets.c | 7 ++++++-
 2 files changed, 10 insertions(+), 3 deletions(-)

2.4.0

Reproducer:

$ qemu-system-x86_64 -display vnc=unix:/root/i-cant-access-you.sock
qemu-system-x86_64: iohandler.c:60: qemu_set_fd_handler2: Assertion `fd >= 0' failed.
Aborted (core dumped)

---
v3:
Fix checkpatch warning

 ui/vnc.c | 3 +++
 1 file changed, 3 insertions(+)

index 9f8ecd0..e1abf64 100644
@@ -3685,6 +3685,9 @@ void vnc_display_open(const char *id, Error **errp)
         /* listen for connects */
         if (strncmp(vnc, "unix:", 5) == 0) {
             vs->lsock = unix_listen(vnc+5, NULL, 0, errp);
+            if (vs->lsock < 0) {
+                goto fail;
+            }
             vs->is_unix = true;
         } else {
             vs->lsock = inet_listen_opts(sopts, 5900, errp);

2.4.0

Before:
qemu-system-x86_64: -display vnc=unix:/root/foo.sock: Failed to start VNC server on `(null)': Failed to bind socket to /root/foo.sock: Permission denied

After:
qemu-system-x86_64: -display vnc=unix:/root/foo.sock: Failed to start VNC server: Failed to bind socket to /root/foo.sock: Permission denied

Rather than tweak the string possibly show unix: value as well, just drop the explicit display reporting. We already get the cli string in the error message, that should be sufficient.

---
v3:
No change

 ui/vnc.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index e1abf64..b3450ec 100644
@@ -3780,8 +3780,7 @@ int vnc_init_func(QemuOpts *opts, void *opaque)
     vnc_display_init(id);
     vnc_display_open(id, &local_err);
     if (local_err != NULL) {
-        error_report("Failed to start VNC server on `%s': %s",
-                     qemu_opt_get(opts, "display"),
+        error_report("Failed to start VNC server: %s",
                      error_get_pretty(local_err));
         error_free(local_err);
         exit(1);

2.4.0

Consider this case:

$ ls -ld ~/root-owned/
drwx--x--x. 2 root root 4096 Apr 29 12:55 /home/crobinso/root-owned/
$ ls -l ~/root-owned/foo.sock
-rwxrwxrwx. 1 crobinso crobinso 0 Apr 29 12:55 /home/crobinso/root-owned/foo.sock

$ qemu-system-x86_64 -vnc unix:~/root-owned/foo.sock
qemu-system-x86_64: -vnc unix:/home/crobinso/root-owned/foo.sock: Failed to start VNC server: Failed to bind socket to /home/crobinso/root-owned/foo.sock: Address already in use

...which is techinically true, but the real error is that we failed to unlink. So report it.

This may seem pathological but it's a real possibility via libvirt.

---
v3:
Fix checkpatch warning

 util/qemu-sockets.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

index 87c9bc6..22c8c4c 100644
@@ -729,7 +729,12 @@ int unix_listen_opts(QemuOpts *opts, Error **errp)
         qemu_opt_set(opts, "path", un.sun_path, &error_abort);
     }
 
-    unlink(un.sun_path);
+    if ((access(un.sun_path, F_OK) == 0) &&
+        unlink(un.sun_path) < 0) {
+        error_setg_errno(errp, errno,
+                         "Failed to unlink socket %s", un.sun_path);
+        goto err;
+    }
     if (bind(sock, (struct sockaddr*) &un, sizeof(un)) < 0) {
         error_setg_errno(errp, errno, "Failed to bind socket to %s", un.sun_path);
         goto err;

2.4.0

added to vnc queue.

thanks,
Gerd