Messages in this thread Patch in this message | | | From | Jan Kara <> | Subject | [PATCH 1/2] lib: Fix strnlen_user() to not touch memory after specified maximum | Date | Tue, 2 Jun 2015 17:10:28 +0200 |
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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.
CC: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jan Kara <jack@suse.cz> --- lib/strnlen_user.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c index a28df5206d95..fd03ae980013 100644 --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -57,7 +57,7 @@ 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))) + if (unlikely(max <= sizeof(unsigned long))) break; max -= sizeof(unsigned long); if (unlikely(__get_user(c,(unsigned long __user *)(src+res)))) -- 2.1.4
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