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Commit a414f01a authored by Linus Torvalds's avatar Linus Torvalds
Browse files

strcmp: fix overflow and possibly signedness error 



Doing the strcmp return value as

	signed char __res = *cs - *ct;

is wrong for two reasons.  The subtraction can overflow because __res
doesn't use a type big enough.  Moreover the compared bytes should be
interpreted as unsigned char as specified by POSIX.

The same problem is fixed in strncmp.

Signed-off-by: default avatarUwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Michael Buesch <mb@bu3sch.de>
Cc: Andreas Schwab <schwab@linux-m68k.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6602b355

lib/string.c

+14 −6
Original line number Diff line number Diff line
@@ -246,13 +246,17 @@ EXPORT_SYMBOL(strlcat); 
#undef strcmp

int strcmp(const char *cs, const char *ct)

{

	signed char __res;

	unsigned char c1, c2;



	while (1) {

		if ((__res = *cs - *ct++) != 0 || !*cs++)

		c1 = *cs++;

		c2 = *ct++;

		if (c1 != c2)

			return c1 < c2 ? -1 : 1;

		if (!c1)

			break;

	}

	return __res;

	return 0;

}

EXPORT_SYMBOL(strcmp);

#endif
@@ -266,14 +270,18 @@ EXPORT_SYMBOL(strcmp); 
 */

int strncmp(const char *cs, const char *ct, size_t count)

{

	signed char __res = 0;

	unsigned char c1, c2;



	while (count) {

		if ((__res = *cs - *ct++) != 0 || !*cs++)

		c1 = *cs++;

		c2 = *ct++;

		if (c1 != c2)

			return c1 < c2 ? -1 : 1;

		if (!c1)

			break;

		count--;

	}

	return __res;

	return 0;

}

EXPORT_SYMBOL(strncmp);

#endif