Commit 1a3241ff authored Feb 01, 2018 by Andrey Ryabinin Committed by Linus Torvalds Feb 01, 2018

lib/strscpy: Shut up KASAN false-positives in strscpy()



strscpy() performs the word-at-a-time optimistic reads.  So it may may
access the memory past the end of the object, which is perfectly fine
since strscpy() doesn't use that (past-the-end) data and makes sure the
optimistic read won't cross a page boundary.

Use new read_word_at_a_time() to shut up the KASAN.

Note that this potentially could hide some bugs.  In example bellow,
stscpy() will copy more than we should (1-3 extra uninitialized bytes):

        char dst[8];
        char *src;

        src = kmalloc(5, GFP_KERNEL);
        memset(src, 0xff, 5);
        strscpy(dst, src, 8);

Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 7f1e541f

lib/string.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -203,7 +203,7 @@ ssize_t strscpy(char dest, const char src, size_t count)
		while (max >= sizeof(unsigned long)) {
		unsigned long c, data;

		c = (unsigned long )(src+res);
		c = read_word_at_a_time(src+res);
		if (has_zero(c, &data, &constants)) {
		data = prep_zero_mask(c, data, &constants);
		data = create_zero_mask(data);

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