Heap: Fix a possible bug in the TLSF allocator
Fix a bug that could return a chunk of memory smaller than requested,
easily leading to a memory corruption, when the required memory alignment
passed to the allocator is 4.
@@ -802,7 +802,11 @@ void* tlsf_memalign_offs(tlsf_t tlsf, size_t align, size_t size, size_t data_off
const size_t size_with_gap = adjust_request_size(adjust + align + gap_minimum - off_adjust, align);
/*
- ** If alignment is less than or equals base alignment, we're done.
+ ** If alignment is less than or equal to base alignment, we're done, because
+ ** we are guaranteed that the size is at least sizeof(block_header_t), enough
+ ** to store next blocks' metadata. Plus, all pointers allocated will all be
+ ** aligned on a 4-byte bound, so ptr + data_offset will also have this
+ ** alignment constraint. Thus, the gap is not required.
** If we requested 0 bytes, return null, as tlsf_malloc(0) does.
*/
const size_t aligned_size = (adjust && align > ALIGN_SIZE) ? size_with_gap : adjust;
@@ -820,10 +824,12 @@ void* tlsf_memalign_offs(tlsf_t tlsf, size_t align, size_t size, size_t data_off
tlsf_cast(tlsfptr_t, aligned) - tlsf_cast(tlsfptr_t, ptr));
/*
- ** If gap size is too small or if there is not gap but we need one,
+ ** If gap size is too small or if there is no gap but we need one,
** offset to next aligned boundary.
+ ** NOTE: No need for a gap if the alignment required is less than or is
+ ** equal to ALIGN_SIZE.
*/
- if ((gap && gap < gap_minimum) || (!gap && off_adjust))
+ if ((gap && gap < gap_minimum) || (!gap && off_adjust && align > ALIGN_SIZE))
{
const size_t gap_remain = gap_minimum - gap;
const size_t offset = tlsf_max(gap_remain, align);
