lib: mempool-allocfree - Do not use PTR_OFFSET with negative offset

Avoids undefined behaviour sanitization error.

diff --git a/src/lib/mempool-allocfree.c b/src/lib/mempool-allocfree.c
index 239f984be14dbdfab14cce858eb85b9b5b8e0300..07b74a89a0b14c2bd1db451da376e718d6911c36 100644 (file)
--- a/src/lib/mempool-allocfree.c
+++ b/src/lib/mempool-allocfree.c
@@ -234,7 +234,9 @@ static void *pool_block_attach(struct allocfree_pool *apool, struct pool_block *
 static struct pool_block *
 pool_block_detach(struct allocfree_pool *apool, unsigned char *mem)
 {
-       struct pool_block *block = PTR_OFFSET(mem, -SIZEOF_POOLBLOCK);
+       /* cannot use PTR_OFFSET because of negative value */
+       i_assert((uintptr_t)mem >= SIZEOF_POOLBLOCK);
+       struct pool_block *block = (struct pool_block *)(mem - SIZEOF_POOLBLOCK);
 
        /* make sure the block we are dealing with is correct */
        i_assert(block->block == mem);