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Subject[PATCH v8 09/12] 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 <>
Signed-off-by: Andrey Ryabinin <>
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;
+ kasan_unpoison_shadow(dname,
+ round_up(name->len + 1, sizeof(unsigned long)));
} else {
dname = dentry->d_iname;

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