[PATCH] libxl: Don't segfault on soft-reset failure

[Jason Andryuk <jandryuk@xxxxxxxxx>]

If domain_soft_reset_cb can't rename the save file, it doesn't call
initiate_domain_create() and calls domcreate_complete().

Skipping initiate_domain_create() means dcs->console_wait is
uninitialized and all 0s.

We have:
  domcreate_complete()
    libxl__xswait_stop()
      libxl__ev_xswatch_deregister().

The uninitialized slotnum 0 is considered valid (-1 is the invalid
sentinel), so the NULL pointer path to passed to xs_unwatch() which
segfaults.

libxl__ev_xswatch_deregister:watch w=0x12bc250 wpath=(null) token=0/0: 
deregister slotnum=0

Ensure dcs->console_xswait is minimally initialized by calling
libxl__xswait_init() in do_domain_soft_reset().

Also add a check for dcs->console_xswait.path being NULL in
domcreate_complete() to avoid the segfault.

Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
---
The NULL check in domcreate_complete isn't needed when the xswait is
initialized, but it could catch other occurances.

 tools/libs/light/libxl_create.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/libs/light/libxl_create.c b/tools/libs/light/libxl_create.c
index 15ed021f41..631caa416d 100644
--- a/tools/libs/light/libxl_create.c
+++ b/tools/libs/light/libxl_create.c
@@ -1970,7 +1970,8 @@ static void domcreate_complete(libxl__egc *egc,
     libxl_domain_config *const d_config = dcs->guest_config;
     libxl_domain_config *d_config_saved = &dcs->guest_config_saved;
 
-    libxl__xswait_stop(gc, &dcs->console_xswait);
+    if (dcs->console_xswait.path)
+        libxl__xswait_stop(gc, &dcs->console_xswait);
 
     libxl__domain_build_state_dispose(&dcs->build_state);
 
@@ -2176,6 +2177,10 @@ static int do_domain_soft_reset(libxl_ctx *ctx,
                               aop_console_how);
     cdcs->domid_out = &domid_out;
 
+    /* Initialize in case we end up in domcreate_complete without calling
+     * initiate_domain_create. */
+    libxl__xswait_init(&cdcs->dcs.console_xswait);
+
     dom_path = libxl__xs_get_dompath(gc, domid);
     if (!dom_path) {
         LOGD(ERROR, domid, "failed to read domain path");
-- 
2.35.1