[PATCH] lib/cmdline: fix integer overflow of the index in get_options()

[lzhan011 <lzsx618@gmail.com>]

From: lzhan011 <zhangleizhen645@gmail.com>

For a range "M-N", get_options() advances its index by the size of the
range:

	i += (range_nums - 1);

get_range() only bounds how many values it stores, but returns the full
size of the range, which can be as large as INT_MAX. The addition then
overflows i, which wraps to a negative value since the kernel is built
with -fno-strict-overflow. As a result:

 - with nints > 0, the loop continues (i < nints still holds) and the
   next get_option() call writes to ints[i], about 8 GiB below the
   array;

 - in validation mode (nints == 0), the returned count is negative or
   bogus, so callers such as parse_int_array() allocate a too small
   array, and the second get_options() pass then performs the same out
   of bounds write.

For example, get_options("0-2147483647", 6, ints) writes to ints[INT_MIN].
parse_int_array() is reachable from several root-writable debugfs
files via parse_int_array_user() (e.g. in sound/soc/sof,
sound/soc/intel/avs, drivers/gpu/drm/xe and
drivers/platform/x86/intel/vsec_tpmi.c), and get_options() is used
directly by e.g. the lux_table sysfs store handlers in
drivers/iio/light/tsl2583.c and tsl2772.c.

Stop parsing if the range would overflow the index, and add a KUnit test
case. Ranges that don't overflow are parsed exactly as before.

Found by fuzzing get_options() and parse_int_array() with ASan/UBSan
in userspace; the new test case fails without this fix.

Fixes: 22f2e2801799 ("[PATCH] get_options to allow a hypenated range for isolcpus")
Assisted-by: Claude:claude-opus-5-5 ASan UBSan libFuzzer
Signed-off-by: lzhan011 <zhangleizhen645@gmail.com>
---
 lib/cmdline.c             |  5 ++++-
 lib/tests/cmdline_kunit.c | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/lib/cmdline.c b/lib/cmdline.c
index 16cce6621..76a4a39ec 100644
--- a/lib/cmdline.c
+++ b/lib/cmdline.c
@@ -125,8 +125,11 @@ char *get_options(const char *str, int nints, int *ints)
 			/*
 			 * Decrement the result by one to leave out the
 			 * last number in the range.  The next iteration
-			 * will handle the upper number in the range
+			 * will handle the upper number in the range.
+			 * Stop if that would overflow @i.
 			 */
+			if (range_nums > INT_MAX - 1 - i)
+				break;
 			i += (range_nums - 1);
 		}
 		i++;
diff --git a/lib/tests/cmdline_kunit.c b/lib/tests/cmdline_kunit.c
index 3f61ff8d3..96e6593ff 100644
--- a/lib/tests/cmdline_kunit.c
+++ b/lib/tests/cmdline_kunit.c
@@ -252,12 +252,31 @@ static void cmdline_test_memparse(struct kunit *test)
 				    "    when parsing '%s'", e->input);
 	}
 }
+static void cmdline_test_range_overflow(struct kunit *test)
+{
+	int r[16];
+
+	/*
+	 * A range spanning (almost) the whole int space must not overflow
+	 * the number of parsed integers; such a range is not counted.
+	 * Only the validation mode is used, as it never writes beyond r[0].
+	 */
+	r[0] = -1;
+	get_options("0-2147483647", 0, r);
+	KUNIT_EXPECT_EQ(test, r[0], 0);
+
+	r[0] = -1;
+	get_options("1,0-2147483647", 0, r);
+	KUNIT_EXPECT_EQ(test, r[0], 1);
+}
+
 
 static struct kunit_case cmdline_test_cases[] = {
 	KUNIT_CASE(cmdline_test_noint),
 	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),
-- 
2.34.1