linux-kernel - [PATCH 4.19 21/88] hex2bin: fix access beyond string end

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Message-Id: <20220510130734.364009494@linuxfoundation.org>
Date:   Tue, 10 May 2022 15:07:06 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mikulas Patocka <mpatocka@...hat.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.19 21/88] hex2bin: fix access beyond string end

From: Mikulas Patocka <mpatocka@...hat.com>

commit e4d8a29997731b3bb14059024b24df9f784288d0 upstream.

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.

Note that hex_to_bin returns -1 on error and hex2bin return -EINVAL on
error - so we can't just return the variable "hi" or "lo" on error.
This inconsistency may be fixed in the next merge window, but for the
purpose of fixing this bug, we just preserve the existing behavior and
return -1 and -EINVAL.

Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@...il.com>
Fixes: b78049831ffe ("lib: add error checking to hex2bin")
Cc: stable@...r.kernel.org
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 lib/hexdump.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/lib/hexdump.c
+++ b/lib/hexdump.c
@@ -66,10 +66,13 @@ 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 (unlikely(hi < 0))
+			return -EINVAL;
+		lo = hex_to_bin(*src++);
+		if (unlikely(lo < 0))
 			return -EINVAL;
 
 		*dst++ = (hi << 4) | lo;