fix invalid read in aligned_alloc

in case of mmap-obtained chunks, end points past the end of the
mapping and reading it may fault. since the value is not needed until
after the conditional, move the access to prevent invalid reads.

diff --git a/src/malloc/aligned_alloc.c b/src/malloc/aligned_alloc.c
index d623420b42c8427bfce2babe8c1a9ce055a939a0..158dba41238a4fd09cf1c4ac181fa3a92b8f94e3 100644 (file)
--- a/src/malloc/aligned_alloc.c
+++ b/src/malloc/aligned_alloc.c
@@ -31,8 +31,6 @@ void *aligned_alloc(size_t align, size_t len)
                return NULL;
 
        header = ((size_t *)mem)[-1];
-       end = mem + (header & -8);
-       footer = ((size_t *)end)[-2];
        new = (void *)((uintptr_t)mem + align-1 & -align);
 
        if (!(header & 7)) {
@@ -41,6 +39,9 @@ void *aligned_alloc(size_t align, size_t len)
                return new;
        }
 
+       end = mem + (header & -8);
+       footer = ((size_t *)end)[-2];
+
        ((size_t *)mem)[-1] = header&7 | new-mem;
        ((size_t *)new)[-2] = footer&7 | new-mem;
        ((size_t *)new)[-1] = header&7 | end-new;