[PATCH] lib/cmdline: fix get_options() count and overflow with large ranges

[Armaan Sandhu <armaan.sandhu0504@gmail.com>]

get_range() stops writing once the array is full, but get_options()
still advances its index by the whole range. So "1-100" parsed into
four ints reports 99 numbers, and a range like "0-2147483647" wraps
the index negative and writes outside the array.

Stop once a range fills the array, bail out in validation mode before
the count overflows, and saturate the range length in get_range().
Add KUnit cases; without the fix "0-2147483647" panics the test kernel.

Only root can supply this input, so this is a robustness fix.

Fixes: 22f2e2801799 ("[PATCH] get_options to allow a hypenated range for isolcpus")
Cc: stable@vger.kernel.org
Signed-off-by: Armaan Sandhu <armaan.sandhu0504@gmail.com>
---
 lib/cmdline.c             | 13 ++++++++++++-
 lib/tests/cmdline_kunit.c | 38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/lib/cmdline.c b/lib/cmdline.c
index 16cce6621cec..40b98d943a9a 100644
--- a/lib/cmdline.c
+++ b/lib/cmdline.c
@@ -11,6 +11,7 @@
 
 #include <linux/export.h>
 #include <linux/kernel.h>
+#include <linux/overflow.h>
 #include <linux/string.h>
 #include <linux/ctype.h>
 
@@ -26,7 +27,9 @@ static int get_range(char **str, int *pint, int n)
 
 	(*str)++;
 	upper_range = simple_strtol((*str), NULL, 0);
-	inc_counter = upper_range - *pint;
+	/* Keep the sign of the result when the difference doesn't fit */
+	if (check_sub_overflow(upper_range, *pint, &inc_counter))
+		inc_counter = upper_range < *pint ? -1 : INT_MAX;
 	for (x = *pint; n && x < upper_range; x++, n--)
 		*pint++ = x;
 	return inc_counter;
@@ -122,6 +125,14 @@ char *get_options(const char *str, int nints, int *ints)
 			range_nums = get_range((char **)&str, pint, n);
 			if (range_nums < 0)
 				break;
+			/* The range didn't fit, so the array is full */
+			if (!validate && range_nums > n) {
+				i = nints;
+				break;
+			}
+			/* Leave room for the upper number of the range */
+			if (range_nums >= INT_MAX - i)
+				break;
 			/*
 			 * Decrement the result by one to leave out the
 			 * last number in the range.  The next iteration
diff --git a/lib/tests/cmdline_kunit.c b/lib/tests/cmdline_kunit.c
index 3f61ff8d3178..584fcb2c0e44 100644
--- a/lib/tests/cmdline_kunit.c
+++ b/lib/tests/cmdline_kunit.c
@@ -140,6 +140,43 @@ static void cmdline_test_range(struct kunit *test)
 	} while (++i < ARRAY_SIZE(cmdline_test_range_strings));
 }
 
+static const struct {
+	const char *in;
+	int parsed[4];
+	int validated;
+} cmdline_test_range_overflow_cases[] = {
+	{ "1-100",         { 3, 1, 2, 3, },    100,        },
+	{ "1,5-100,7",     { 3, 1, 5, 6, },    98,         },
+	{ "1-2147483646",  { 3, 1, 2, 3, },    2147483646, },
+	{ "0-2147483647",  { 3, 0, 1, 2, },    0,          },
+	{ "-5-2147483647", { 3, -5, -4, -3, }, 0,          },
+	{ "2147483647--5", { 0, 2147483647, }, 0,          },
+};
+
+static void cmdline_test_range_overflow(struct kunit *test)
+{
+	unsigned int i, j;
+
+	for (i = 0; i < ARRAY_SIZE(cmdline_test_range_overflow_cases); i++) {
+		const char *in = cmdline_test_range_overflow_cases[i].in;
+		const int *e = cmdline_test_range_overflow_cases[i].parsed;
+		/* Two guard elements past the array handed to get_options() */
+		int r[ARRAY_SIZE(cmdline_test_range_overflow_cases[0].parsed) + 2];
+		int n;
+
+		memset(r, 0, sizeof(r));
+		get_options(in, ARRAY_SIZE(r) - 2, r);
+		for (j = 0; j < ARRAY_SIZE(r) - 2; j++)
+			KUNIT_EXPECT_EQ_MSG(test, r[j], e[j], "Pattern: %s at %u", in, j);
+		for (; j < ARRAY_SIZE(r); j++)
+			KUNIT_EXPECT_EQ_MSG(test, r[j], 0, "Pattern: %s out of bound at %u", in, j);
+
+		get_options(in, 0, &n);
+		KUNIT_EXPECT_EQ_MSG(test, n, cmdline_test_range_overflow_cases[i].validated,
+				    "Pattern: %s (validated)", in);
+	}
+}
+
 static void cmdline_test_next_arg_quoted_value(struct kunit *test)
 {
 	char in[] = "foo=\"bar baz\" qux=1";
@@ -258,6 +295,7 @@ static struct kunit_case cmdline_test_cases[] = {
 	KUNIT_CASE(cmdline_test_lead_int),
 	KUNIT_CASE(cmdline_test_tail_int),
 	KUNIT_CASE(cmdline_test_range),
+	KUNIT_CASE(cmdline_test_range_overflow),
 	KUNIT_CASE(cmdline_test_next_arg_quoted_value),
 	KUNIT_CASE(cmdline_test_next_arg_bare_quote_regression),
 	KUNIT_CASE(cmdline_test_next_arg_mixed_tokens),
-- 
2.55.0