strcmp: fix overflow and possibly signedness error (a414f01a) · Commits · 戴 / test

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:

Uwe 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:

Linus Torvalds <torvalds@linux-foundation.org>

lib/string.c

+14 −6

Original line number	Original line	Diff line number	Diff line
	@@ -246,13 +246,17 @@ EXPORT_SYMBOL(strlcat);
	#undef strcmp		#undef strcmp
	int strcmp(const char cs, const char ct)		int strcmp(const char cs, const char ct)
	{		{
	signed char __res;		unsigned char c1, c2;

	while (1) {		while (1) {
	if ((__res = cs - ct++) != 0 \|\| !*cs++)		c1 = *cs++;
			c2 = *ct++;
			if (c1 != c2)
			return c1 < c2 ? -1 : 1;
			if (!c1)
	break;		break;
	}		}
	return __res;		return 0;
	}		}
	EXPORT_SYMBOL(strcmp);		EXPORT_SYMBOL(strcmp);
	#endif		#endif
	@@ -266,14 +270,18 @@ EXPORT_SYMBOL(strcmp);
	*/		*/
	int strncmp(const char cs, const char ct, size_t count)		int strncmp(const char cs, const char ct, size_t count)
	{		{
	signed char __res = 0;		unsigned char c1, c2;

	while (count) {		while (count) {
	if ((__res = cs - ct++) != 0 \|\| !*cs++)		c1 = *cs++;
			c2 = *ct++;
			if (c1 != c2)
			return c1 < c2 ? -1 : 1;
			if (!c1)
	break;		break;
	count--;		count--;
	}		}
	return __res;		return 0;
	}		}
	EXPORT_SYMBOL(strncmp);		EXPORT_SYMBOL(strncmp);
	#endif		#endif

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