[xen master] libs/guest: Fix leak on realloc failure in backup_ptes()

[patchbot@xxxxxxx]

commit 275d13184cfa52ebe4336ed66526ce93716adbe0
Author:     Edwin Török <edwin.torok@xxxxxxxxx>
AuthorDate: Fri Feb 24 13:03:44 2023 +0000
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Feb 27 15:51:23 2023 +0000

    libs/guest: Fix leak on realloc failure in backup_ptes()
    
    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 â??reallocâ?? fails
      |      |         |               (92) â??old_ptes.entriesâ?? leaks here; 
was allocated at (44)
      |      |         (90) ...to here
    
    Signed-off-by: Edwin Török <edwin.torok@xxxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 tools/libs/guest/xg_offline_page.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/libs/guest/xg_offline_page.c 
b/tools/libs/guest/xg_offline_page.c
index c594fdba41..ccd0299f0f 100644
--- a/tools/libs/guest/xg_offline_page.c
+++ b/tools/libs/guest/xg_offline_page.c
@@ -181,10 +181,16 @@ static int backup_ptes(xen_pfn_t table_mfn, int offset,
 
     if (backup->max == backup->cur)
     {
-        backup->entries = realloc(backup->entries,
-                            backup->max * 2 * sizeof(struct pte_backup_entry));
+        void *orig = backup->entries;
+
+        backup->entries = realloc(
+            orig, backup->max * 2 * sizeof(struct pte_backup_entry));
+
         if (backup->entries == NULL)
+        {
+            free(orig);
             return -1;
+        }
         else
             backup->max *= 2;
     }
--
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