[PATCH] off-by-one bugs found by valgrind

[PATCH] off-by-one bugs found by valgrind

[Pavel Roskin]

Insufficient memory is allocated in index-pack.c to hold the *.idx name.
One more byte should be allocated to hold the terminating 0.

quote_c_style_counted() in quote.c uses a dangerous construct, when a
variable is incremented once and used twice in the same expression.
Convert this construct to a more traditional form of the for loop.

Signed-off-by: Pavel Roskin <proski@gnu.org>

diff --git a/index-pack.c b/index-pack.c
index 785fe71..d4ce3af 100644
--- a/index-pack.c
+++ b/index-pack.c
@@ -440,7 +440,7 @@ int main(int argc, char **argv)
 		if (len < 5 || strcmp(pack_name + len - 5, ".pack"))
 			die("packfile name '%s' does not end with '.pack'",
 			    pack_name);
-		index_name_buf = xmalloc(len - 1);
+		index_name_buf = xmalloc(len);
 		memcpy(index_name_buf, pack_name, len - 5);
 		strcpy(index_name_buf + len - 5, ".idx");
 		index_name = index_name_buf;
diff --git a/quote.c b/quote.c
index 76eb144..00297b5 100644
--- a/quote.c
+++ b/quote.c
@@ -126,8 +126,10 @@ static int quote_c_style_counted(const c
 
 	if (!no_dq)
 		EMIT('"');
-	for (sp = name; (ch = *sp++) && (sp - name) <= namelen; ) {
-
+	for (sp = name; sp < name + namelen; sp++) {
+		ch = *sp;
+		if (!ch)
+			break;
 		if ((ch < ' ') || (ch == '"') || (ch == '\\') ||
 		    (ch == 0177)) {
 			needquote = 1;


-- 
Regards,
Pavel Roskin

Re: [PATCH] off-by-one bugs found by valgrind

[Junio C Hamano]

Pavel Roskin <proski@gnu.org> writes:

> Insufficient memory is allocated in index-pack.c to hold the *.idx name.
> One more byte should be allocated to hold the terminating 0.

Thanks.

> quote_c_style_counted() in quote.c uses a dangerous construct, when a
> variable is incremented once and used twice in the same expression.

Sorry, I do not follow you.  Isn't && a sequence point?

> -	for (sp = name; (ch = *sp++) && (sp - name) <= namelen; ) {
> -
> +	for (sp = name; sp < name + namelen; sp++) {

Re: [PATCH] off-by-one bugs found by valgrind

[H. Peter Anvin]

Junio C Hamano wrote:
> Pavel Roskin <proski@gnu.org> writes:
> 
> 
>>Insufficient memory is allocated in index-pack.c to hold the *.idx name.
>>One more byte should be allocated to hold the terminating 0.
> 
> Thanks.
> 
> 
>>quote_c_style_counted() in quote.c uses a dangerous construct, when a
>>variable is incremented once and used twice in the same expression.
> 
> Sorry, I do not follow you.  Isn't && a sequence point?
> 

&& is a sequence point.  The code is techically fine, but it's harder 
than necessary to read.

	-hpa

Re: [PATCH] off-by-one bugs found by valgrind

[Pavel Roskin]

On Wed, 2005-12-21 at 13:17 -0800, H. Peter Anvin wrote:
> >>quote_c_style_counted() in quote.c uses a dangerous construct, when a
> >>variable is incremented once and used twice in the same expression.
> > 
> > Sorry, I do not follow you.  Isn't && a sequence point?

The patch is right, but my comment was wrong, sorry.

The actual problem detected by valgrind is that sp is dereferenced
before it's checked for the upper boundary.  So, if e.g. namelen is 6,
the code reads name[6] into ch and then leaves the loop.

> && is a sequence point.  The code is techically fine, but it's harder 
> than necessary to read.

That alone should be a good reason to apply this patch.

-- 
Regards,
Pavel Roskin

Re: [PATCH] off-by-one bugs found by valgrind

[Horst von Brand]

Junio C Hamano <junkio@cox.net> wrote:
> Pavel Roskin <proski@gnu.org> writes:

[...]

> > quote_c_style_counted() in quote.c uses a dangerous construct, when a
> > variable is incremented once and used twice in the same expression.
> 
> Sorry, I do not follow you.  Isn't && a sequence point?
> 
> > -	for (sp = name; (ch = *sp++) && (sp - name) <= namelen; ) {
> > -
> > +	for (sp = name; sp < name + namelen; sp++) {

Yes, it is, so it doesn't fix any bugs; but Pavel's version is definitely
more readable.
-- 
Dr. Horst H. von Brand                   User #22616 counter.li.org
Departamento de Informatica                     Fono: +56 32 654431
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