[linux-next][PATCH v2] mm/slub.c: add a naive detection of double free or corruption

[Alexander Popov <alex.popov@linux.com>]

Add an assertion similar to "fasttop" check in GNU C Library allocator
as a part of SLAB_FREELIST_HARDENED feature. An object added to a singly
linked freelist should not point to itself. That helps to detect some
double free errors (e.g. CVE-2017-2636) without slub_debug and KASAN.

Signed-off-by: Alexander Popov <alex.popov@linux.com>
---
 mm/slub.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/slub.c b/mm/slub.c
index b9c7f1a..77b2781 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -290,6 +290,10 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp)
 {
 	unsigned long freeptr_addr = (unsigned long)object + s->offset;
 
+#ifdef CONFIG_SLAB_FREELIST_HARDENED
+	BUG_ON(object == fp); /* naive detection of double free or corruption */
+#endif
+
 	*(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr);
 }
 
-- 
2.7.4

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