[PATCH] getaddrinfo: Fix leak with AI_ALL [BZ #28852]

[Siddhesh Poyarekar <siddhesh@sourceware.org>]

Avoid allocating multiple blocks in convert_hostent_to_gaih_addrtuple
because it's not possible to free the second block in the caller
gaih_inet.  Instead, use realloc and fix up pointers in the result list.

Resolves BZ #28852.

Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
---
This is for 2.36; I'll backport the fix to 2.35 after the release is
cut.

Tested check and xcheck on x86_64 and also verified using valgrind that
the reproducer in the bugzilla is fixed.  mtrace doesn't show this leak
for some reason, so the reproducer could not be adapted to a glibc test
case.

 sysdeps/posix/getaddrinfo.c | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/sysdeps/posix/getaddrinfo.c b/sysdeps/posix/getaddrinfo.c
index 18dccd5924..652a1a43d4 100644
--- a/sysdeps/posix/getaddrinfo.c
+++ b/sysdeps/posix/getaddrinfo.c
@@ -199,9 +199,6 @@ convert_hostent_to_gaih_addrtuple (const struct addrinfo *req,
 				   struct hostent *h,
 				   struct gaih_addrtuple **result)
 {
-  while (*result)
-    result = &(*result)->next;
-
   /* Count the number of addresses in h->h_addr_list.  */
   size_t count = 0;
   for (char **p = h->h_addr_list; *p != NULL; ++p)
@@ -212,10 +209,30 @@ convert_hostent_to_gaih_addrtuple (const struct addrinfo *req,
   if (count == 0 || h->h_length > sizeof (((struct gaih_addrtuple) {}).addr))
     return true;
 
-  struct gaih_addrtuple *array = calloc (count, sizeof (*array));
+  struct gaih_addrtuple *array = *result;
+  size_t old = 0;
+
+  while (array)
+    {
+      old++;
+      array = array->next;
+    }
+
+  array = realloc (*result, (old + count) * sizeof (*array));
+
   if (array == NULL)
     return false;
 
+  *result = array;
+
+  /* Update the next pointers on reallocation.  */
+  for (size_t i = 0; i < old; i++)
+    array[i].next = array + i + 1;
+
+  array += old;
+
+  memset (array, 0, count * sizeof (*array));
+
   for (size_t i = 0; i < count; ++i)
     {
       if (family == AF_INET && req->ai_family == AF_INET6)
@@ -235,7 +252,6 @@ convert_hostent_to_gaih_addrtuple (const struct addrinfo *req,
   array[0].name = h->h_name;
   array[count - 1].next = NULL;
 
-  *result = array;
   return true;
 }
 
-- 
2.34.1