From f18c34e483ff6b1d9866472221e4015b3a4698e4 Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Tue, 2 Jun 2015 17:10:28 +0200 Subject: [PATCH] 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 Cc: stable@vger.kernel.org Signed-off-by: Linus Torvalds --- lib/strnlen_user.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c index a28df5206d95..11649615c505 100644 --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -57,7 +57,8 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count, 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)))) -- 2.20.1