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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?
Thanks, Florian
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