Fix wrong zmalloc_size() assumption. (#7963)

When using a system with no malloc_usable_size(), zmalloc_size() assumed
that the heap allocator always returns blocks that are long-padded.

This may not always be the case, and will result with zmalloc_size()
returning a size that is bigger than allocated. At least in one case
this leads to out of bound write, process crash and a potential security
vulnerability.

Effectively this does not affect the vast majority of users, who use
jemalloc or glibc.

This problem along with a (different) fix was reported by Drew DeVault.

(cherry picked from commit 9824fe3e392caa04dc1b4071886e9ac402dd6d95)
(cherry picked from commit ce0d74d8fdff55d07929f562ec9acf2d00caf893)

1 files changed, 0 insertions, 3 deletions

diff --git a/src/zmalloc.c b/src/zmalloc.c
index dd655620c..972db79d7 100644
--- a/src/zmalloc.c
+++ b/src/zmalloc.c
@@ -177,9 +177,6 @@ void *zrealloc(void *ptr, size_t size) {
 size_t zmalloc_size(void *ptr) {
     void *realptr = (char*)ptr-PREFIX_SIZE;
     size_t size = *((size_t*)realptr);
-    /* Assume at least that all the allocations are padded at sizeof(long) by
-     * the underlying allocator. */
-    if (size&(sizeof(long)-1)) size += sizeof(long)-(size&(sizeof(long)-1));
     return size+PREFIX_SIZE;
 }
 size_t zmalloc_usable(void *ptr) {