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Subject[PATCH] strcmp: fix overflow and possibly signedness error
Date
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
--
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