[xen stable-4.15] libxl: check return value of libxl__xs_directory in name2bdf

[patchbot@xxxxxxx]

commit d470a54087e0fbd813dae4d773ad0b830eeec4a1
Author:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
AuthorDate: Tue Jul 12 11:26:58 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jul 12 11:26:58 2022 +0200

    libxl: check return value of libxl__xs_directory in name2bdf
    
    libxl__xs_directory() can potentially return NULL without setting `n`.
    As `n` isn't initialised, we need to check libxl__xs_directory()
    return value before checking `n`. Otherwise, `n` might be non-zero
    with `bdfs` NULL which would lead to a segv.
    
    Fixes: 57bff091f4 ("libxl: add 'name' field to 'libxl_device_pci' in the 
IDL...")
    Reported-by: "G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Tested-by: "G.R." <firemeteor@xxxxxxxxxxxxxxxxxxxxx>
    master commit: d778089ac70e5b8e3bdea0c85fc8c0b9ed0eaf2f
    master date: 2022-07-12 08:38:51 +0200
---
 tools/libs/light/libxl_pci.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
index 92bf86b2be..a5f5cdf62b 100644
--- a/tools/libs/light/libxl_pci.c
+++ b/tools/libs/light/libxl_pci.c
@@ -859,7 +859,7 @@ static int name2bdf(libxl__gc *gc, libxl_device_pci *pci)
     int rc = ERROR_NOTFOUND;
 
     bdfs = libxl__xs_directory(gc, XBT_NULL, PCI_INFO_PATH, &n);
-    if (!n)
+    if (!bdfs || !n)
         goto out;
 
     for (i = 0; i < n; i++) {
--
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