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authorKees Cook <keescook@chromium.org>2021-09-19 01:17:53 +0300
committerKees Cook <keescook@chromium.org>2022-02-17 01:29:48 +0300
commite1be43d9b5d0d1310dbd90185a8e5c7145dde40f (patch)
tree5004e987b78a18f951501f0466e4f578822ea275 /include/linux/overflow.h
parent8e7c8ca6b988904d4c32c4053b325739738c8f36 (diff)
downloadlinux-e1be43d9b5d0d1310dbd90185a8e5c7145dde40f.tar.xz
overflow: Implement size_t saturating arithmetic helpers
In order to perform more open-coded replacements of common allocation size arithmetic, the kernel needs saturating (SIZE_MAX) helpers for multiplication, addition, and subtraction. For example, it is common in allocators, especially on realloc, to add to an existing size: 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(), size_add(), and size_sub() helpers that implicitly promote arguments to size_t and saturated calculations for use in 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 new helpers use __must_check, though what is really desired is a way to make sure that assignment is only to a size_t lvalue. Without this, it's still possible to introduce overflow/underflow via type conversion (i.e. from size_t to int). Enforcing this will currently need to be left to static analysis or future use of -Wconversion. Additionally update the overflow unit tests to force runtime evaluation for the pathological cases. Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Gustavo A. R. Silva <gustavoars@kernel.org> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Jason Gunthorpe <jgg@ziepe.ca> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Leon Romanovsky <leon@kernel.org> Cc: Keith Busch <kbusch@kernel.org> Cc: Len Baker <len.baker@gmx.com> Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'include/linux/overflow.h')
-rw-r--r--include/linux/overflow.h110
1 files changed, 69 insertions, 41 deletions
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 4669632bd72b..59d7228104d0 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -118,81 +118,94 @@ static inline bool __must_check __must_check_overflow(bool overflow)
}))
/**
- * array_size() - Calculate size of 2-dimensional array.
- *
- * @a: dimension one
- * @b: dimension two
+ * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
*
- * Calculates size of 2-dimensional array: @a * @b.
+ * @factor1: first factor
+ * @factor2: second factor
*
- * Returns: number of bytes needed to represent the array or SIZE_MAX on
- * overflow.
+ * Returns: calculate @factor1 * @factor2, both promoted to size_t,
+ * with any overflow causing the return value to be SIZE_MAX. The
+ * lvalue must be size_t to avoid implicit type conversion.
*/
-static inline __must_check size_t array_size(size_t a, size_t b)
+static inline size_t __must_check size_mul(size_t factor1, size_t factor2)
{
size_t bytes;
- if (check_mul_overflow(a, b, &bytes))
+ if (check_mul_overflow(factor1, factor2, &bytes))
return SIZE_MAX;
return bytes;
}
/**
- * array3_size() - Calculate size of 3-dimensional array.
+ * size_add() - Calculate size_t addition with saturation at SIZE_MAX
*
- * @a: dimension one
- * @b: dimension two
- * @c: dimension three
- *
- * Calculates size of 3-dimensional array: @a * @b * @c.
+ * @addend1: first addend
+ * @addend2: second addend
*
- * Returns: number of bytes needed to represent the array or SIZE_MAX on
- * overflow.
+ * Returns: calculate @addend1 + @addend2, both promoted to size_t,
+ * with any overflow causing the return value to be SIZE_MAX. The
+ * lvalue must be size_t to avoid implicit type conversion.
*/
-static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)
+static inline size_t __must_check size_add(size_t addend1, size_t addend2)
{
size_t bytes;
- if (check_mul_overflow(a, b, &bytes))
- return SIZE_MAX;
- if (check_mul_overflow(bytes, c, &bytes))
+ if (check_add_overflow(addend1, addend2, &bytes))
return SIZE_MAX;
return bytes;
}
-/*
- * Compute a*b+c, returning SIZE_MAX on overflow. Internal helper for
- * struct_size() below.
+/**
+ * size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX
+ *
+ * @minuend: value to subtract from
+ * @subtrahend: value to subtract from @minuend
+ *
+ * Returns: calculate @minuend - @subtrahend, both promoted to size_t,
+ * with any overflow causing the return value to be SIZE_MAX. For
+ * composition with the size_add() and size_mul() helpers, neither
+ * argument may be SIZE_MAX (or the result with be forced to SIZE_MAX).
+ * The lvalue must be size_t to avoid implicit type conversion.
*/
-static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
+static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
{
size_t bytes;
- if (check_mul_overflow(a, b, &bytes))
- return SIZE_MAX;
- if (check_add_overflow(bytes, c, &bytes))
+ if (minuend == SIZE_MAX || subtrahend == SIZE_MAX ||
+ check_sub_overflow(minuend, subtrahend, &bytes))
return SIZE_MAX;
return bytes;
}
/**
- * struct_size() - Calculate size of structure with trailing array.
- * @p: Pointer to the structure.
- * @member: Name of the array member.
- * @count: Number of elements in the array.
+ * array_size() - Calculate size of 2-dimensional array.
*
- * Calculates size of memory needed for structure @p followed by an
- * array of @count number of @member elements.
+ * @a: dimension one
+ * @b: dimension two
*
- * Return: number of bytes needed or SIZE_MAX on overflow.
+ * Calculates size of 2-dimensional array: @a * @b.
+ *
+ * Returns: number of bytes needed to represent the array 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 array_size(a, b) size_mul(a, b)
+
+/**
+ * array3_size() - Calculate size of 3-dimensional array.
+ *
+ * @a: dimension one
+ * @b: dimension two
+ * @c: dimension three
+ *
+ * Calculates size of 3-dimensional array: @a * @b * @c.
+ *
+ * Returns: number of bytes needed to represent the array or SIZE_MAX on
+ * overflow.
+ */
+#define array3_size(a, b, c) size_mul(size_mul(a, b), c)
/**
* flex_array_size() - Calculate size of a flexible array member
@@ -208,7 +221,22 @@ static inline __must_check size_t __ab_c_size(size_t a, size_t b, size_t c)
* 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))
+ size_mul(count, \
+ sizeof(*(p)->member) + __must_be_array((p)->member))
+
+/**
+ * struct_size() - Calculate size of structure with trailing flexible array.
+ *
+ * @p: Pointer to the structure.
+ * @member: Name of the 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.
+ *
+ * Return: number of bytes needed or SIZE_MAX on overflow.
+ */
+#define struct_size(p, member, count) \
+ size_add(sizeof(*(p)), flex_array_size(p, member, count))
#endif /* __LINUX_OVERFLOW_H */