Messages in this thread Patch in this message | | | From | Uwe Kleine-König <> | Subject | [PATCH] strcmp: fix overflow and possibly signedness error | Date | Wed, 18 Nov 2009 22:31:52 +0100 |
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From: Linus Torvalds <torvalds@linux-foundation.org>
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> Cc: Linus Torvalds <torvalds@linux-foundation.org> --- Hello Linus,
I resend with a (hopefully) nice commit log as this didn't appear in your tree up to now.
Best regards Uwe
lib/string.c | 20 ++++++++++++++------ 1 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/lib/string.c b/lib/string.c index b19b87a..e96421a 100644 --- a/lib/string.c +++ b/lib/string.c @@ -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 -- 1.6.5.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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