[PATCH v1 2/2] backup_ptes: fix leak on realloc failure

[Edwin Török <edvin.torok@xxxxxxxxxx>]

From: Edwin Török <edwin.torok@xxxxxxxxx>

>From `man 2 realloc`:
`If realloc() fails, the original block is left untouched; it is not freed or 
moved.`

Found using GCC -fanalyzer:
```
|  184 |         backup->entries = realloc(backup->entries,
|      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|      |         |               | |
|      |         |               | (91) when ‘realloc’ fails
|      |         |               (92) ‘old_ptes.entries’ leaks here; was 
allocated at (44)
|      |         (90) ...to here
```

Signed-off-by: Edwin Török <edwin.torok@xxxxxxxxx>
---
 tools/libs/guest/xg_offline_page.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/libs/guest/xg_offline_page.c 
b/tools/libs/guest/xg_offline_page.c
index c594fdba41..a8bcea768b 100644
--- a/tools/libs/guest/xg_offline_page.c
+++ b/tools/libs/guest/xg_offline_page.c
@@ -181,10 +181,13 @@ static int backup_ptes(xen_pfn_t table_mfn, int offset,
 
     if (backup->max == backup->cur)
     {
-        backup->entries = realloc(backup->entries,
+        void* orig = backup->entries;
+        backup->entries = realloc(orig,
                             backup->max * 2 * sizeof(struct pte_backup_entry));
-        if (backup->entries == NULL)
+        if (backup->entries == NULL) {
+            free(orig);
             return -1;
+        }
         else
             backup->max *= 2;
     }
-- 
2.39.1