[monitoring-plugins] check_http: Fix memory reallocation error in ...

[Lorenz Kästle]

 Module: monitoring-plugins
 Branch: fix_1829
 Commit: d9528c265b96a5a0f0c2e43ac74ab3921a2987e1
 Author: Lorenz Kästle <12514511+RincewindsHat at users.noreply.github.com>
   Date: Mon Jan 30 12:45:20 2023 +0100
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=d9528c2

check_http: Fix memory reallocation error in chunk decoding logic

This patch should fix an error with the way memory reallocation was
used, which resulted in "realloc(): invalid next size".
It is not completely clear to me as to what caused this problem, but
apparently one can not depend handing a pointer to "realloc(3)" and
expect that it still works afterwards, but one should/must use the one
returned by the function.

Also this patch replaces a variable which was used to remember the
position in the array by just computing that from the current values.

---

 plugins/check_http.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/plugins/check_http.c b/plugins/check_http.c
index a9c2238..c23625e 100644
--- a/plugins/check_http.c
+++ b/plugins/check_http.c
@@ -1399,7 +1399,6 @@ char *unchunk_content(const char *content) {
   char *endptr;
   long length_of_chunk = 0;
   size_t overall_size = 0;
-  char *result_ptr;
 
   while (true) {
     size_of_chunk = strtol(pointer, &endptr, 16);
@@ -1446,7 +1445,6 @@ char *unchunk_content(const char *content) {
         }
         return NULL;
       }
-      result_ptr = result;
     } else {
       void *tmp = realloc(result, overall_size);
       if (tmp == NULL) {
@@ -1454,11 +1452,12 @@ char *unchunk_content(const char *content) {
           printf("Failed to allocate memory for unchunked body\n");
         }
         return NULL;
+      } else {
+        result = tmp;
       }
     }
 
-    memcpy(result_ptr, start_of_chunk, size_of_chunk);
-    result_ptr = result_ptr + size_of_chunk;
+    memcpy(result + (overall_size - size_of_chunk), start_of_chunk, size_of_chunk);
   }
 
   result[overall_size] = '\0';