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Date: Mon, 20 Sep 2021 11:08:52 -0700
From: Kees Cook <keescook@...omium.org>
To: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Kees Cook <keescook@...omium.org>,
"Gustavo A . R . Silva" <gustavoars@...nel.org>,
Nathan Chancellor <nathan@...nel.org>,
Jason Gunthorpe <jgg@...pe.ca>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Leon Romanovsky <leon@...nel.org>,
Keith Busch <kbusch@...nel.org>, Len Baker <len.baker@....com>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH 1/2] overflow: Implement size_t saturating arithmetic helpers
In order to perform more open-coded replacements of common allocation
size arithmetic, the kernel needs a saturating (SIZE_MAX) helper for
addition and multiplication. It is common in allocators, especially on
realloc, to add to an existing size. For example:
p = krealloc(map->patch,
sizeof(struct reg_sequence) * (map->patch_regs + num_regs),
GFP_KERNEL);
There is no existing saturating replacement for this calculation, and
just leaving the addition open coded inside array_size() could
potentially overflow as well. For example, an overflow in an expression
for a size_t argument might wrap to zero:
array_size(anything, something_at_size_max + 1) == 0
Introduce size_mul() and size_add() helpers to perform size_t promotion
and saturated calculations for use in such allocations. With these
helpers it is also possible to redefine array_size(), array3_size(),
flex_array_size(), and struct_size() in terms of the new helpers.
As with the check_*_overflow() helpers, the helpers are wrapped in a
__must_check function that passes through the size_t result. In order
for the helpers to be composed with themselves, they must have unique
variable names to avoid shadowing, so this uses a similar method to what
is already done in minmax.h for constructing unique names to be passed
in as arguments to the statement expression that does the actual work.
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: Leon Romanovsky <leon@...nel.org>
Cc: Keith Busch <kbusch@...nel.org>
Cc: Len Baker <len.baker@....com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
include/linux/overflow.h | 140 ++++++++++++++++++++++++---------------
lib/test_overflow.c | 61 +++++++++++++++++
2 files changed, 149 insertions(+), 52 deletions(-)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 4669632bd72b..cd154d47807c 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -117,6 +117,77 @@ static inline bool __must_check __must_check_overflow(bool overflow)
(*_d >> _to_shift) != _a); \
}))
+/*
+ * As with __must_check_overflow() above, this is used to wrap the
+ * size_t output from a statement expression macro.
+ */
+static inline size_t __must_check __must_check_size(size_t size)
+{
+ return size;
+}
+
+/*
+ * Internal logic for size_mul(). Takes variable names from UNIQUE_ID
+ * so that the local variables here will never collide with other local
+ * variables (for example, with itself).
+ */
+#define __size_mul(factor1, factor2, __factor1, __factor2, __product) \
+({ \
+ size_t __product; \
+ size_t __factor1 = (factor1); \
+ size_t __factor2 = (factor2); \
+ if (check_mul_overflow(__factor1, __factor2, &__product)) \
+ __product = SIZE_MAX; \
+ __product; \
+})
+
+/**
+ * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
+ *
+ * @factor1: first factor
+ * @factor2: second factor
+ *
+ * Returns: calculate @factor1 * @factor2, where both values are
+ * evaluated as size_t, with any overflow causing the return value to
+ * be SIZE_MAX.
+ */
+#define size_mul(factor1, factor2) \
+ __must_check_size(__size_mul(factor1, factor2, \
+ __UNIQUE_ID(__factor1_), \
+ __UNIQUE_ID(__factor2_), \
+ __UNIQUE_ID(__product_)))
+
+/*
+ * Internal logic for size_add(). Takes variable names from UNIQUE_ID
+ * so that the local variables here will never collide with other local
+ * variables (for example, with itself).
+ */
+#define __size_add(addend1, addend2, __addend1, __addend2, __sum) \
+({ \
+ size_t __sum; \
+ size_t __addend1 = (addend1); \
+ size_t __addend2 = (addend2); \
+ if (check_add_overflow(__addend1, __addend2, &__sum)) \
+ __sum = SIZE_MAX; \
+ __sum; \
+})
+
+/**
+ * size_add() - Calculate size_t addition with saturation at SIZE_MAX
+ *
+ * @addend1: first addend
+ * @addend2: second addend
+ *
+ * Returns: calculate @addend1 + @addend2, where both values are
+ * evaluated as size_t, with any overflow causing the return value to
+ * be SIZE_MAX.
+ */
+#define size_add(addend1, addend2) \
+ __must_check_size(__size_add(addend1, addend2, \
+ __UNIQUE_ID(__addend1_), \
+ __UNIQUE_ID(__addend2_), \
+ __UNIQUE_ID(__sum_)))
+
/**
* array_size() - Calculate size of 2-dimensional array.
*
@@ -128,15 +199,7 @@ static inline bool __must_check __must_check_overflow(bool overflow)
* Returns: number of bytes needed to represent the array or SIZE_MAX on
* overflow.
*/
-static inline __must_check size_t array_size(size_t a, size_t b)
-{
- size_t bytes;
-
- if (check_mul_overflow(a, b, &bytes))
- return SIZE_MAX;
-
- return bytes;
-}
+#define array_size(a, b) size_mul(a, b)
/**
* array3_size() - Calculate size of 3-dimensional array.
@@ -150,65 +213,38 @@ static inline __must_check size_t array_size(size_t a, size_t b)
* Returns: number of bytes needed to represent the array or SIZE_MAX on
* overflow.
*/
-static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
-{
- size_t bytes;
-
- if (check_mul_overflow(a, b, &bytes))
- return SIZE_MAX;
- if (check_mul_overflow(bytes, c, &bytes))
- return SIZE_MAX;
-
- return bytes;
-}
-
-/*
- * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
- * struct_size() below.
- */
-static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
-{
- size_t bytes;
-
- if (check_mul_overflow(a, b, &bytes))
- return SIZE_MAX;
- if (check_add_overflow(bytes, c, &bytes))
- return SIZE_MAX;
-
- return bytes;
-}
+#define array3_size(a, b, c) size_mul(size_mul(a, b), c)
/**
- * struct_size() - Calculate size of structure with trailing array.
+ * flex_array_size() - Calculate size of a flexible array member
+ * within an enclosing structure.
+ *
* @p: Pointer to the structure.
- * @member: Name of the array member.
+ * @member: Name of the flexible array member.
* @count: Number of elements in the array.
*
- * Calculates size of memory needed for structure @p followed by an
- * array of @count number of @member elements.
+ * Calculates size of a flexible array of @count number of @member
+ * elements, at the end of structure @p.
*
* Return: number of bytes needed or SIZE_MAX on overflow.
*/
-#define struct_size(p, member, count) \
- __ab_c_size(count, \
- sizeof(*(p)->member) + __must_be_array((p)->member),\
- sizeof(*(p)))
+#define flex_array_size(p, member, count) \
+ size_mul(count, \
+ sizeof(*(p)->member) + __must_be_array((p)->member))
/**
- * flex_array_size() - Calculate size of a flexible array member
- * within an enclosing structure.
+ * struct_size() - Calculate size of structure with trailing flexible array.
*
* @p: Pointer to the structure.
- * @member: Name of the flexible array member.
+ * @member: Name of the array member.
* @count: Number of elements in the array.
*
- * Calculates size of a flexible array of @count number of @member
- * elements, at the end of structure @p.
+ * Calculates size of memory needed for structure @p followed by an
+ * array of @count number of @member elements.
*
* Return: number of bytes needed or SIZE_MAX on overflow.
*/
-#define flex_array_size(p, member, count) \
- array_size(count, \
- sizeof(*(p)->member) + __must_be_array((p)->member))
+#define struct_size(p, member, count) \
+ size_add(sizeof(*(p)), flex_array_size(p, member, count))
#endif /* __LINUX_OVERFLOW_H */
diff --git a/lib/test_overflow.c b/lib/test_overflow.c
index 7a4b6f6c5473..01a469ff7ff6 100644
--- a/lib/test_overflow.c
+++ b/lib/test_overflow.c
@@ -588,12 +588,73 @@ static int __init test_overflow_allocation(void)
return err;
}
+struct __test_flex_array {
+ unsigned long flags;
+ size_t count;
+ unsigned long data[];
+};
+
+static int __init test_overflow_size_helpers(void)
+{
+ struct __test_flex_array *obj;
+ int count = 0;
+ int err = 0;
+
+#define check_one_size_helper(expected, func, args...) ({ \
+ bool __failure = false; \
+ size_t _r; \
+ \
+ _r = func(args); \
+ if (_r != (expected)) { \
+ pr_warn("expected " #func "(" #args ") " \
+ "to return %zu but got %zu instead\n", \
+ (size_t)(expected), _r); \
+ __failure = true; \
+ } \
+ count++; \
+ __failure; \
+})
+
+ err |= check_one_size_helper(5, size_add, 2, 3);
+ err |= check_one_size_helper(SIZE_MAX, size_add, SIZE_MAX, 1);
+ err |= check_one_size_helper(SIZE_MAX, size_add, SIZE_MAX, 3);
+ err |= check_one_size_helper(SIZE_MAX, size_add, SIZE_MAX, -3);
+
+ err |= check_one_size_helper(6, size_mul, 2, 3);
+ err |= check_one_size_helper(SIZE_MAX, size_mul, SIZE_MAX, 1);
+ err |= check_one_size_helper(SIZE_MAX, size_mul, SIZE_MAX, 3);
+ err |= check_one_size_helper(SIZE_MAX, size_mul, SIZE_MAX, -3);
+
+ err |= check_one_size_helper(0, flex_array_size, obj, data, 0);
+ err |= check_one_size_helper(sizeof(*obj->data),
+ flex_array_size, obj, data, 1);
+ err |= check_one_size_helper(7 * sizeof(*obj->data),
+ flex_array_size, obj, data, 7);
+ err |= check_one_size_helper(SIZE_MAX,
+ flex_array_size, obj, data, -1);
+ err |= check_one_size_helper(SIZE_MAX,
+ flex_array_size, obj, data, SIZE_MAX - 4);
+
+ err |= check_one_size_helper(sizeof(*obj), struct_size, obj, data, 0);
+ err |= check_one_size_helper(sizeof(*obj) + sizeof(*obj->data),
+ struct_size, obj, data, 1);
+ err |= check_one_size_helper(SIZE_MAX,
+ struct_size, obj, data, -3);
+ err |= check_one_size_helper(SIZE_MAX,
+ struct_size, obj, data, SIZE_MAX - 3);
+
+ pr_info("%d overflow size helper tests finished\n", count);
+
+ return err;
+}
+
static int __init test_module_init(void)
{
int err = 0;
err |= test_overflow_calculation();
err |= test_overflow_shift();
+ err |= test_overflow_size_helpers();
err |= test_overflow_allocation();
if (err) {
--
2.30.2
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