Commit f18c34e4 authored Jun 02, 2015 by Jan Kara Committed by Linus Torvalds Jun 02, 2015

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>

parent c46a024e

lib/strnlen_user.c

+2 −1

Original line number	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;
		}
		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))))

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