linux-kernel - [PATCH] hex2bin: fix access beyond string end

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Date:   Sun, 24 Apr 2022 16:48:20 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Shevchenko <andy@...nel.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
cc:     dm-devel@...hat.com, linux-kernel@...r.kernel.org,
        Mike Snitzer <msnitzer@...hat.com>,
        Milan Broz <gmazyland@...il.com>
Subject: [PATCH] hex2bin: fix access beyond string end

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@...hat.com>
Cc: stable@...r.kernel.org

---
 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;