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Commit f18c34e4 authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
Browse files

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: default avatarJan Kara <jack@suse.cz>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c46a024e

lib/strnlen_user.c

+2 −1
Original line number Original line Diff line number Diff line
@@ -57,7 +57,8 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count, 
			return res + find_zero(data) + 1 - align;

			return res + find_zero(data) + 1 - align;

		}

		}

		res += sizeof(unsigned long);

		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;

			break;

		max -= sizeof(unsigned long);

		max -= sizeof(unsigned long);

		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))

		if (unlikely(__get_user(c,(unsigned long __user *)(src+res))))