From 40f31a90505a7da26a8b08aacfbf551cf46f620e Mon Sep 17 00:00:00 2001
From: Sebastian Sumpf <sebastian.sumpf@genode-labs.com>
Date: Thu, 18 May 2023 21:16:20 +0200
Subject: [PATCH] libc: add message for corrupted allocation on 'free'

In case the meta data (or more) got zeroed upon 'free', print error
message. The offset in the meta data can never be zero. This does not
help on other memory corruptions, but at least gives a hint in the too
much zeroed out case.

issue #4675
---
 repos/libports/src/lib/libc/malloc.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/repos/libports/src/lib/libc/malloc.cc b/repos/libports/src/lib/libc/malloc.cc
index 0ec76918ef..f9af5efb6b 100644
--- a/repos/libports/src/lib/libc/malloc.cc
+++ b/repos/libports/src/lib/libc/malloc.cc
@@ -221,6 +221,10 @@ class Libc::Malloc
 
 			void *alloc_addr = (void *)((addr_t)ptr - md->offset);
 
+			if (md->offset == 0)
+				error("libc free: meta-data offset is 0 for address: ", ptr,
+				      " - corrupted allocation");
+
 			if (msb > SLAB_STOP) {
 				_backing_store.free(alloc_addr, real_size);
 			} else {