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Subject[PATCH v10 08/17] fs: dcache: manually unpoison dname after allocation to shut up kasan's reports
Date
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 | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/fs/dcache.c b/fs/dcache.c
index 1467ab9..dc400fd 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"

@@ -1539,6 +1541,9 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
}
atomic_set(&p->u.count, 1);
dname = p->name;
+ if (IS_ENABLED(CONFIG_DCACHE_WORD_ACCESS))
+ kasan_unpoison_shadow(dname,
+ round_up(name->len + 1, sizeof(unsigned long)));
} else {
dname = dentry->d_iname;
}
--
2.2.2


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