linux-kernel - Fw: [PATCH] cmdline: fix get_options() overflow while parsing ranges

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Message-ID: <20170620113518.638eac2f@lwn.net>
Date:   Tue, 20 Jun 2017 11:35:18 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ilya Matveychikov <matvejchikov@...il.com>
Subject: Fw: [PATCH] cmdline: fix get_options() overflow while parsing
 ranges

Andrew, this seems to have fallen through the cracks.  It addresses a
real bug with possible security considerations and should probably get
merged with a CC: stable...?

jon

Begin forwarded message:

Date: Mon, 22 May 2017 19:53:47 +0400
From: Ilya Matveychikov <matvejchikov@...il.com>
To: linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: [PATCH] cmdline: fix get_options() overflow while parsing ranges


When using get_options() it's possible to specify a range of numbers,
like 1-100500. The problem is that it doesn't track array size while
calling internally to get_range() which iterates over the range and
fills the memory with numbers.

Signed-off-by: Ilya V. Matveychikov <matvejchikov@...il.com>
---
 lib/cmdline.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/cmdline.c b/lib/cmdline.c
index 8f13cf7..79069d7 100644
--- a/lib/cmdline.c
+++ b/lib/cmdline.c
@@ -22,14 +22,14 @@
  *	the values[M, M+1, ..., N] into the ints array in get_options.
  */
 
-static int get_range(char **str, int *pint)
+static int get_range(char **str, int *pint, int n)
 {
 	int x, inc_counter, upper_range;
 
 	(*str)++;
 	upper_range = simple_strtol((*str), NULL, 0);
 	inc_counter = upper_range - *pint;
-	for (x = *pint; x < upper_range; x++)
+	for (x = *pint; n && x < upper_range; x++, n--)
 		*pint++ = x;
 	return inc_counter;
 }
@@ -96,7 +96,7 @@ char *get_options(const char *str, int nints, int *ints)
 			break;
 		if (res == 3) {
 			int range_nums;
-			range_nums = get_range((char **)&str, ints + i);
+			range_nums = get_range((char **)&str, ints + i, nints - i);
 			if (range_nums < 0)
 				break;
 			/*
-- 
2.7.4