[PATCH 4/5] fs/dcache: Use read_word_at_a_time() in dentry_string_cmp()

[Andrey Ryabinin]

dentry_string_cmp() performs the word-at-a-time reads from 'cs' and may
read slightly more than it was requested in kmallac(). Normally this
would make KASAN to report out-of-bounds access, but this was workarounded
by commit df4c0e36f1b1 ("fs: dcache: manually unpoison dname after
allocation to shut up kasan's reports").

This workaround is not perfect, since it allows out-of-bounds access
to dentry's name for all the code, not just in dentry_string_cmp().

So it would be better to use read_word_at_a_time() instead and
revert commit df4c0e36f1b1.

Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
---
 fs/dcache.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index c99812fd54b3..195999c8d1b4 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -193,7 +193,7 @@ static inline int dentry_string_cmp(const unsigned char *cs, const unsigned char
 	unsigned long a,b,mask;
 
 	for (;;) {
-		a = *(unsigned long *)cs;
+		a = read_word_at_a_time(cs);
 		b = load_unaligned_zeropad(ct);
 		if (tcount < sizeof(unsigned long))
 			break;
-- 
2.13.6