xl network-attach SEGV in 4.2 and 4.1

[Marek Marczykowski <marmarek@invisiblethingslab.com>]

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Hi all,

4.2 and 4.1 suffers from SEGV during xl network-attach in
libxl__device_nic_add. In 4.3-unstable it is fixed by:
5420f2650 libxl: Set vfb and vkb devid if not done so by the caller

So either the patch need to be backported to 4.1 and 4.2, or fixed by this one:
- ------
libxl: Fix SEGV in network-attach

When "device/vif" directory exists but is empty l!=NULL, but nb==0, so
l[nb-1] is invalid. Add missing check.

Signed-Off-by: Marek Marczykowski <marmarek@invisiblethingslab.com>

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 5783cd2..9e06a7d 100644
- --- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2569,7 +2569,8 @@ void libxl__device_nic_add(libxl__egc *egc, uint32_t
domid,
             goto out_free;
         }
         if (!(l = libxl__xs_directory(gc, XBT_NULL,
- -                                     libxl__sprintf(gc, "%s/device/vif",
dompath), &nb))) {
+                                     libxl__sprintf(gc, "%s/device/vif",
dompath), &nb)) ||
+                nb == 0) {
             nic->devid = 0;
         } else {
             nic->devid = strtoul(l[nb - 1], NULL, 10) + 1;

- -- 
Best Regards / Pozdrawiam,
Marek Marczykowski
Invisible Things Lab
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