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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2009-11-18 22:31:52 +0100 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-11-18 17:18:13 -0800 |
| commit | a414f01ac2899f273ef8fe98fa44158ac12793f2 (patch) | |
| tree | 30a7ef8d7d2f8d4aca0781fa8785630fc1f6320d /lib/string.c | |
| parent | 6602b355c2cf8f4c628732827408606075288d28 (diff) | |
| download | lwn-a414f01ac2899f273ef8fe98fa44158ac12793f2.tar.gz lwn-a414f01ac2899f273ef8fe98fa44158ac12793f2.zip | |
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: 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>
Diffstat (limited to 'lib/string.c')
| -rw-r--r-- | lib/string.c | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/lib/string.c b/lib/string.c index b19b87af65a3..e96421ab9a9a 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 |