[PATCH v2] hex2bin: fix access beyond string end

[Mikulas Patocka]

On Tue, 26 Apr 2022, Andy Shevchenko wrote:

> On Sun, Apr 24, 2022 at 10:48 PM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> >
> > If we pass too short string to "hex2bin" (and the string size without the
> > terminating NUL character is even), "hex2bin" reads one byte after the
> > terminating NUL character. This patch fixes it.
> >
> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > Cc: stable@xxxxxxxxxxxxxxx
> 
> You need to provide a Fixes tag.

OK. Here I resend it with the "Fixes" tag.

> And on top of that it would be nice to understand if we need to
> support half-bytes, but in any case it's not a scope of the patch
> right now.

Do you think that there are any users who need this?

> -- 
> With Best Regards,
> Andy Shevchenko

Mikulas



From: Mikulas Patocka <mpatocka@xxxxxxxxxx>

If we pass too short string to "hex2bin" (and the string size without the
terminating NUL character is even), "hex2bin" reads one byte after the
terminating NUL character. This patch fixes it.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Fixes: b78049831ffe ("lib: add error checking to hex2bin")
Cc: stable@xxxxxxxxxxxxxxx

---
 lib/hexdump.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

Index: linux-2.6/lib/hexdump.c
===================================================================
--- linux-2.6.orig/lib/hexdump.c	2022-04-24 18:51:16.000000000 +0200
+++ linux-2.6/lib/hexdump.c	2022-04-24 18:51:16.000000000 +0200
@@ -45,10 +45,13 @@ EXPORT_SYMBOL(hex_to_bin);
 int hex2bin(u8 *dst, const char *src, size_t count)
 {
 	while (count--) {
-		int hi = hex_to_bin(*src++);
-		int lo = hex_to_bin(*src++);
+		int hi, lo;
 
-		if ((hi < 0) || (lo < 0))
+		hi = hex_to_bin(*src++);
+		if (hi < 0)
+			return -EINVAL;
+		lo = hex_to_bin(*src++);
+		if (lo < 0)
 			return -EINVAL;
 
 		*dst++ = (hi << 4) | lo;