[PATCH 01/16] malloc: Fix a realloc crash with heap tagging [BZ 27468]

[Szabolcs Nagy]

_int_free must be called with a chunk that has its tag reset. This was
missing in a rare case that could crash when heap tagging is enabled:
when in a multi-threaded process the current arena runs out of memory
during realloc, but another arena still has space to finish the realloc
then _int_free was called without clearing the user allocation tags.

And another _int_free call site in realloc used the wrong size for the
tag clearing: the chunk header of the next chunk was also cleared which
in practice is probably not a problem, but logically that belongs to a
different chunk so it may cause trouble.

Fixes bug 27468.
---
 malloc/malloc.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/malloc/malloc.c b/malloc/malloc.c
index 1f4bbd8edf..10ea6aa441 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -3446,7 +3446,9 @@ __libc_realloc (void *oldmem, size_t bytes)
       newp = __libc_malloc (bytes);
       if (newp != NULL)
         {
-          memcpy (newp, oldmem, oldsize - SIZE_SZ);
+	  size_t sz = CHUNK_AVAILABLE_SIZE (oldp) - CHUNK_HDR_SZ;
+	  memcpy (newp, oldmem, sz);
+	  (void) TAG_REGION (chunk2rawmem (oldp), sz);
           _int_free (ar_ptr, oldp, 0);
         }
     }
@@ -4850,10 +4852,10 @@ _int_realloc(mstate av, mchunkptr oldp, INTERNAL_SIZE_T oldsize,
           else
             {
 	      void *oldmem = chunk2mem (oldp);
+	      size_t sz = CHUNK_AVAILABLE_SIZE (oldp) - CHUNK_HDR_SZ;
 	      newmem = TAG_NEW_USABLE (newmem);
-	      memcpy (newmem, oldmem,
-		      CHUNK_AVAILABLE_SIZE (oldp) - CHUNK_HDR_SZ);
-	      (void) TAG_REGION (chunk2rawmem (oldp), oldsize);
+	      memcpy (newmem, oldmem, sz);
+	      (void) TAG_REGION (chunk2rawmem (oldp), sz);
               _int_free (av, oldp, 1);
               check_inuse_chunk (av, newp);
               return chunk2mem (newp);
-- 
2.17.1