lib: Fix strnlen_user() to not touch memory after specified maximum
If the specified maximum length of the string is a multiple of unsigned
long, we would load one long behind the specified maximum. If that
happens to be in a next page, we can hit a page fault although we were
not expected to.
Fix the off-by-one bug in the test whether we are at the end of the
specified range.
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index a28df52..1164961 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -57,7 +57,8 @@
return res + find_zero(data) + 1 - align;
}
res += sizeof(unsigned long);
- if (unlikely(max < sizeof(unsigned long)))
+ /* We already handled 'unsigned long' bytes. Did we do it all ? */
+ if (unlikely(max <= sizeof(unsigned long)))
break;
max -= sizeof(unsigned long);
if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))