[PATCH 2/4] libm/stdlib: don't read past source in nano_realloc

[Keith Packard <keithp@keithp.com>]

Save the computed block size and use it to avoid reading past
the end of the source block.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 newlib/libc/stdlib/nano-mallocr.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/newlib/libc/stdlib/nano-mallocr.c b/newlib/libc/stdlib/nano-mallocr.c
index 04465eb9e..cef23977e 100644
--- a/newlib/libc/stdlib/nano-mallocr.c
+++ b/newlib/libc/stdlib/nano-mallocr.c
@@ -466,6 +466,7 @@ void * nano_realloc(RARG void * ptr, malloc_size_t size)
 {
     void * mem;
     chunk * p_to_realloc;
+    malloc_size_t old_size;
 
     if (ptr == NULL) return nano_malloc(RCALL size);
 
@@ -477,12 +478,15 @@ void * nano_realloc(RARG void * ptr, malloc_size_t size)
 
     /* TODO: There is chance to shrink the chunk if newly requested
      * size is much small */
-    if (nano_malloc_usable_size(RCALL ptr) >= size)
+    old_size = nano_malloc_usable_size(RCALL ptr);
+    if (old_size >= size)
       return ptr;
 
     mem = nano_malloc(RCALL size);
     if (mem != NULL)
     {
+	if (size > old_size)
+	    size = old_size;
         memcpy(mem, ptr, size);
         nano_free(RCALL ptr);
     }
-- 
2.28.0