diff options
authorJan Kara <>2015-06-02 17:10:28 +0200
committerGreg Kroah-Hartman <>2015-06-06 08:19:32 -0700
commit9ad68dc3f6f155f6a8bda0bb8837c854a9db2ff2 (patch)
parent7bbf0eb78d91361497ce6dbb787cf1625cbaeb1a (diff)
lib: Fix strnlen_user() to not touch memory after specified maximum
commit f18c34e483ff6b1d9866472221e4015b3a4698e4 upstream. 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 <> Signed-off-by: Linus Torvalds <> Signed-off-by: Greg Kroah-Hartman <>
1 files changed, 2 insertions, 1 deletions
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)))
max -= sizeof(unsigned long);
if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))