lib: fix _parse_integer_limit() to handle overflow

Patch series "lib and lib/cmdline enhancements", v11.

This series is a merge of the recently posted [1] and [2].  The first one
is intended to adjust '_parse_integer_limit()' and 'memparse()' to not
ignore overflows, extend string to 64-bit integer conversion tests, add
KUnit-based test for 'memparse()' and fix kernel-doc glitches found in
lib/cmdline.c.  The second one was originated from RISCV-specific build
fixes needed to integrate the former and now aims to provide
platform-specific double-word shifts and corresponding KUnit test.

Getting feedback from RISCV core maintainers would be very helpful.

Special thanks to Andy Shevchenko, Charlie Jenkins, and Andrew Morton.

This patch (of 8):

In '_parse_integer_limit()', adjust native integer arithmetic with
near-to-overflow branch where 'check_mul_overflow()' and
'check_add_overflow()' are used to check whether an intermediate result
goes out of range, and denote such a case with ULLONG_MAX, thus making the
function more similar to standard C library's 'strtoull()'.  Adjust
comment to kernel-doc style as well.

Link: https://lore.kernel.org/20260519172259.908980-1-dmantipov@yandex.ru
Link: https://lore.kernel.org/20260519172259.908980-2-dmantipov@yandex.ru
Link: https://lore.kernel.org/linux-riscv/20260403103338.1122415-1-dmantipov@yandex.ru
Link: https://lore.kernel.org/linux-riscv/20260427090105.705529-1-dmantipov@yandex.ru
Signed-off-by: Dmitry Antipov <dmantipov@yandex.ru>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Andriy Shevchenko <andriy.shevchenko@intel.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Charlie Jenkins <thecharlesjenkins@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/lib/kstrtox.c b/lib/kstrtox.c
index 97be2a39f537105af99f3c4a2044db76743e3f54..edc4eb7c1bca184a28f98ecc0786584381c5c234 100644 (file)
--- a/lib/kstrtox.c
+++ b/lib/kstrtox.c
@@ -39,25 +39,30 @@ const char *_parse_integer_fixup_radix(const char *s, unsigned int *base)
        return s;
 }
 
-/*
- * Convert non-negative integer string representation in explicitly given radix
- * to an integer. A maximum of max_chars characters will be converted.
+/**
+ * _parse_integer_limit - Convert integer string representation to an integer
+ * @s: Integer string representation
+ * @base: Radix
+ * @p: Where to store result
+ * @max_chars: Maximum amount of characters to convert
+ *
+ * Convert non-negative integer string representation in explicitly given
+ * radix to an integer. If overflow occurs, value at @p is set to ULLONG_MAX.
  *
- * Return number of characters consumed maybe or-ed with overflow bit.
- * If overflow occurs, result integer (incorrect) is still returned.
+ * This function is the workhorse of other string conversion functions and it
+ * is discouraged to use it explicitly. Consider kstrto*() family instead.
  *
- * Don't you dare use this function.
+ * Return: Number of characters consumed, maybe ORed with overflow bit
  */
 noinline
 unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned long long *p,
                                  size_t max_chars)
 {
+       unsigned int rv, overflow = 0;
        unsigned long long res;
-       unsigned int rv;
 
        res = 0;
-       rv = 0;
-       while (max_chars--) {
+       for (rv = 0; rv < max_chars; rv++, s++) {
                unsigned int c = *s;
                unsigned int lc = _tolower(c);
                unsigned int val;
@@ -76,15 +81,17 @@ unsigned int _parse_integer_limit(const char *s, unsigned int base, unsigned lon
                 * it in the max base we support (16)
                 */
                if (unlikely(res & (~0ull << 60))) {
-                       if (res > div_u64(ULLONG_MAX - val, base))
-                               rv |= KSTRTOX_OVERFLOW;
+                       if (check_mul_overflow(res, base, &res) ||
+                           check_add_overflow(res, val, &res)) {
+                               res = ULLONG_MAX;
+                               overflow = KSTRTOX_OVERFLOW;
+                       }
+               } else {
+                       res = res * base + val;
                }
-               res = res * base + val;
-               rv++;
-               s++;
        }
        *p = res;
-       return rv;
+       return rv | overflow;
 }
 
 noinline