linux-kernel - [PATCH v3 10/13] fs: dcache: manually unpoison dname after allocation to shut up kasan's reports

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Date:	Wed, 24 Sep 2014 16:44:06 +0400
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	linux-kernel@...r.kernel.org
Cc:	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Dave Jones <davej@...hat.com>,
	x86@...nel.org, linux-mm@...ck.org,
	Alexander Viro <viro@...iv.linux.org.uk>
Subject: [PATCH v3 10/13] fs: dcache: manually unpoison dname after allocation
 to shut up kasan's reports

We need to manually unpoison rounded up allocation size for dname
to avoid kasan's reports in dentry_string_cmp().
When CONFIG_DCACHE_WORD_ACCESS=y dentry_string_cmp may access
few bytes beyound requested in kmalloc() size.

dentry_string_cmp() relates on that fact that dentry allocated
using kmalloc and kmalloc internally round up allocation size.
So this is not a bug, but this makes kasan to complain about
such accesses.
To avoid such reports we mark rounded up allocation size in
shadow as accessible.

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>
---
 fs/dcache.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 8552986..7811eb2 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -38,6 +38,7 @@
 #include <linux/prefetch.h>
 #include <linux/ratelimit.h>
 #include <linux/list_lru.h>
+#include <linux/kasan.h>
 #include "internal.h"
 #include "mount.h"
 
@@ -1395,6 +1396,10 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 			kmem_cache_free(dentry_cache, dentry); 
 			return NULL;
 		}
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+		kasan_unpoison_shadow(dname,
+				round_up(name->len + 1,	sizeof(unsigned long)));
+#endif
 	} else  {
 		dname = dentry->d_iname;
 	}	
-- 
2.1.1

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