From: Aki Tuomi <aki.tuomi@open-xchange.com>
Date: Tue, 1 Sep 2020 08:54:50 +0000 (+0300)
Subject: lib: mempool-allocfree - Do not use PTR_OFFSET with negative offset
X-Git-Tag: 2.3.13~88
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=3aed1e852ac697a112bdc6ab8edb2d1f0ffb1095;p=thirdparty%2Fdovecot%2Fcore.git

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 239f984be1..07b74a89a0 100644
--- 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);