On 01/16/2018 01:05 PM, Istvan Kurucsai wrote:
Andreas already pointed out style issues.
I'm somewhat surprised that we have accurate accounting in
av->system_mem.
Furthermore, for non-main arenas, I think the check should be against
the
size of a single heap, or maybe the minimum of av->system_mem and
that size.
I thought about this and believe that we can ensure something more
strict: that the end of the top chunk is the same as the end of the
arena (contiguous main_arena case) or the heap (mmapped arena case),
see below. Tests passed but I'm a bit uncertain if these invariants
are always held.
Ensure that the end of the top chunk is the same as
the end of the arena/heap.
* malloc/malloc.c (_int_malloc): Check top size.
---
malloc/malloc.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/malloc/malloc.c b/malloc/malloc.c
index f5aafd2..fd0f001 100644
--- a/malloc/malloc.c
+++ b/malloc/malloc.c
@@ -2251,6 +2251,33 @@ do_check_malloc_state (mstate av)
}
#endif
+static bool
+valid_top_chunk (mstate av, mchunkptr top)
+{
+ size_t size = chunksize(top);
+
+ assert (av);
I think we can drop that assert, it is implied by the pointer
dereference in the subsequent assert.
+ assert (av->top != initial_top (av));
+
+ if (av == &main_arena)
+ {
+ if ((contiguous (&main_arena)
+ && __glibc_unlikely ((uintptr_t) top + size
+ != (uintptr_t) mp_.sbrk_base +
av->system_mem))
+ || (!contiguous (&main_arena)
+ && __glibc_unlikely (size > av->system_mem)))
+ return false;
+ }
+ else
+ {
+ heap_info *heap = heap_for_ptr (top);
+ uintptr_t heap_end = (uintptr_t) heap + heap->size;
+ if (__glibc_unlikely ((uintptr_t) top + size != heap_end))
+ return false;
+ }
+
+ return true;
+}
I wonder if it is possible to write this in a slightly clearer way.
Maybe add a nested if (contiguous (&main_arena)) for the first branch,
and directly return the value of the inner-most conditional?