From: Andrey Ryabinin <a.ryabinin@samsung.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrey Ryabinin <a.ryabinin@samsung.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Konstantin Serebryany <kcc@google.com>,
        Dmitry Chernenkov <dmitryc@google.com>,
        Andrey Konovalov <adech.fo@gmail.com>,
        Yuri Gribov <tetra2005@gmail.com>,
        Konstantin Khlebnikov <koct9i@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>, Christoph Lameter <cl@linux.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Dave Hansen <dave.hansen@intel.com>, Andi Kleen <andi@firstfloor.org>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH v8 09/12] fs: dcache: manually unpoison dname after allocation
 to shut up kasan's reports
Date: Thu, 27 Nov 2014 19:00:53 +0300
Message-id: <1417104057-20335-10-git-send-email-a.ryabinin@samsung.com>
In-reply-to: <1417104057-20335-1-git-send-email-a.ryabinin@samsung.com>
References: <1404905415-9046-1-git-send-email-a.ryabinin@samsung.com>
 <1417104057-20335-1-git-send-email-a.ryabinin@samsung.com>
Sender: linux-kernel-owner@vger.kernel.org

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@google.com>
Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
---
 fs/dcache.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index e368d4f..81561c8 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -38,6 +38,8 @@
 #include <linux/prefetch.h>
 #include <linux/ratelimit.h>
 #include <linux/list_lru.h>
+#include <linux/kasan.h>
+
 #include "internal.h"
 #include "mount.h"
 
@@ -1430,6 +1432,10 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 		}
 		atomic_set(&p->u.count, 1);
 		dname = p->name;
+#ifdef CONFIG_DCACHE_WORD_ACCESS
+		kasan_unpoison_shadow(dname,
+				round_up(name->len + 1,	sizeof(unsigned long)));
+#endif
 	} else  {
 		dname = dentry->d_iname;
 	}	
-- 
2.1.3

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