linux-kernel - [PATCH -mm] argv_split-teach-it-to-handle-mutable-strings-fix-2

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Date:	Tue, 19 Mar 2013 20:54:27 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Lucas De Marchi <lucas.de.marchi@...il.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Paul Mackerras <paulus@...ba.org>, david@...son.dropbear.id.au,
	Kees Cook <keescook@...omium.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Feng Hong <hongfeng@...vell.com>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>
Subject: [PATCH -mm] argv_split-teach-it-to-handle-mutable-strings-fix-2

On 03/18, Andrew Morton wrote:
>
> On Sat, 16 Mar 2013 21:23:53 +0100 Oleg Nesterov <oleg@...hat.com> wrote:
>
> > +	argv_str = kstrndup(str, KMALLOC_MAX_SIZE, gfp);
>
> kstrndup() does kmalloc_track_caller(len+1, gfp) so your
> KMALLOC_MAX_SIZE is off-by-one?

Yes... 'max' is strlen(), not sizeof()...

Actually we could even use ULONG_MAX, the last zero byte in "str" should
be never overwritten. Or we could use some "reasonable" and lower limit.

But I agree, kstrndup(KMALLOC_MAX_SIZE) doesn't look good, please find
fix-2 below.

> From reading the code it is rather unobvious why things were
> implemented in this fashion.  People may come along in five years and
> "clean it up".  Hence we should explain, no?

Yes, thanks for this comment!
---
 lib/argv_split.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/lib/argv_split.c b/lib/argv_split.c
index cac7ec4..e927ed0 100644
--- a/lib/argv_split.c
+++ b/lib/argv_split.c
@@ -63,7 +63,7 @@ char **argv_split(gfp_t gfp, const char *str, int *argcp)
 	char **argv, **argv_ret;
 	int argc;
 
-	argv_str = kstrndup(str, KMALLOC_MAX_SIZE, gfp);
+	argv_str = kstrndup(str, KMALLOC_MAX_SIZE - 1, gfp);
 	if (!argv_str)
 		return NULL;
 
-- 
1.5.5.1


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