[xen master] tools/libs/guest: assist gcc13's realloc analyzer

[patchbot@xxxxxxx]

commit 99a9c3d7141063ae3f357892c6181cfa3be8a280
Author:     Olaf Hering <olaf@xxxxxxxxx>
AuthorDate: Wed May 3 15:06:41 2023 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed May 3 15:06:41 2023 +0200

    tools/libs/guest: assist gcc13's realloc analyzer
    
    gcc13 fails to track the allocated memory in backup_ptes:
    
    xg_offline_page.c: In function 'backup_ptes':
    xg_offline_page.c:191:13: error: pointer 'orig' may be used after 'realloc' 
[-Werror=use-after-free]
      191 |             free(orig);
    
    Assist the analyzer by slightly rearranging the code:
    In case realloc succeeds, the previous allocation is either extended
    or released internally. In case realloc fails, the previous allocation
    is left unchanged. Return an error in this case, the caller will
    release the currently allocated memory in its error path.
    
    http://bugzilla.suse.com/show_bug.cgi?id=1210570
    
    Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Compile-tested-by: Jason Andryuk <jandryuk@xxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 tools/libs/guest/xg_offline_page.c | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/tools/libs/guest/xg_offline_page.c 
b/tools/libs/guest/xg_offline_page.c
index ccd0299f0f..8f0a252417 100644
--- a/tools/libs/guest/xg_offline_page.c
+++ b/tools/libs/guest/xg_offline_page.c
@@ -181,18 +181,14 @@ static int backup_ptes(xen_pfn_t table_mfn, int offset,
 
     if (backup->max == backup->cur)
     {
-        void *orig = backup->entries;
+        void *entries = realloc(backup->entries, backup->max * 2 *
+                                sizeof(struct pte_backup_entry));
 
-        backup->entries = realloc(
-            orig, backup->max * 2 * sizeof(struct pte_backup_entry));
-
-        if (backup->entries == NULL)
-        {
-            free(orig);
+        if (entries == NULL)
             return -1;
-        }
-        else
-            backup->max *= 2;
+
+        backup->entries = entries;
+        backup->max *= 2;
     }
 
     backup->entries[backup->cur].table_mfn = table_mfn;
--
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