RFC: ext4: Add a few overflow checks in the writing code

Some memory allocations make use of data from the disk, so add some
overflow checks.

Adjust LOG2_BLOCK_SIZE() so it is easier to read.

Note: This is a trial to help figure out the best way to deal with these
sorts of things. Feedback welcome.

Series-to: u-boot
Series-cc: heinrich

Signed-off-by: Simon Glass <simon.glass@canonical.com>

common/bloblist.c

@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: GPL-2.0+
+// SPDX-License-Identifier: GPL-2.0+ BSD-3-Clause
 /*
  * Copyright 2018 Google, Inc
  * Written by Simon Glass <sjg@chromium.org>

fs/ext4/ext4_write.c

@@ -25,7 +25,6 @@
 #include <malloc.h>
 #include <memalign.h>
 #include <part.h>
-#include <linux/overflow.h>
 #include <linux/stat.h>
 #include <div64.h>
 #include "ext4_common.h"
@@ -112,7 +111,7 @@ int ext4fs_get_bgdtable(void)
 	size_t alloc_size;
 	int gdsize_total;
 
-	if (check_mul_overflow(fs->no_blkgrp, fs->gdsize, &alloc_size))
+	if (__builtin_mul_overflow(fs->no_blkgrp, fs->gdsize, &alloc_size))
 		return -1;
 	gdsize_total = ROUND(alloc_size, fs->blksz);
 	fs->no_blk_pergdt = gdsize_total / fs->blksz;
@@ -644,7 +643,7 @@ int ext4fs_init(void)
 	}
 
 	/* load all the available bitmap block of the partition */
-	if (check_mul_overflow(fs->no_blkgrp, sizeof(char *), &alloc_size))
+	if (__builtin_mul_overflow(fs->no_blkgrp, sizeof(char *), &alloc_size))
 		goto fail;
 	fs->blk_bmaps = zalloc(alloc_size);
 	if (!fs->blk_bmaps)

include/bloblist.h

@@ -1,4 +1,4 @@
-/* SPDX-License-Identifier: GPL-2.0+ */
+/* SPDX-License-Identifier: GPL-2.0+ BSD-3-Clause */
 /*
  * This provides a standard way of passing information between boot phases
  * (TPL -> SPL -> U-Boot proper.)

include/limits.h

@@ -3,8 +3,6 @@
 #ifndef _LIMITS_H
 #define _LIMITS_H
 
-#include <linux/limits.h>
-
 #define INT_MAX     0x7fffffff
 #define UINT_MAX    0xffffffffU
 #define CHAR_BIT    8

include/linux/kernel.h

@@ -16,6 +16,18 @@
 #define LLONG_MIN	(-LLONG_MAX - 1)
 #define ULLONG_MAX	(~0ULL)
 
+#define U8_MAX		((u8)~0U)
+#define S8_MAX		((s8)(U8_MAX>>1))
+#define S8_MIN		((s8)(-S8_MAX - 1))
+#define U16_MAX		((u16)~0U)
+#define S16_MAX		((s16)(U16_MAX>>1))
+#define S16_MIN		((s16)(-S16_MAX - 1))
+#define U32_MAX		((u32)~0U)
+#define S32_MAX		((s32)(U32_MAX>>1))
+#define S32_MIN		((s32)(-S32_MAX - 1))
+#define U64_MAX		((u64)~0ULL)
+#define S64_MAX		((s64)(U64_MAX>>1))
+#define S64_MIN		((s64)(-S64_MAX - 1))
 
 #define INT32_MAX	S32_MAX
 

include/linux/limits.h

@@ -1,21 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_LIMITS_H
-#define _LINUX_LIMITS_H
-
-#include <linux/types.h>
-
-#define U8_MAX		((u8)~0U)
-#define S8_MAX		((s8)(U8_MAX >> 1))
-#define S8_MIN		((s8)(-S8_MAX - 1))
-#define U16_MAX		((u16)~0U)
-#define S16_MAX		((s16)(U16_MAX >> 1))
-#define S16_MIN		((s16)(-S16_MAX - 1))
-#define U32_MAX		((u32)~0U)
-#define U32_MIN		((u32)0)
-#define S32_MAX		((s32)(U32_MAX >> 1))
-#define S32_MIN		((s32)(-S32_MAX - 1))
-#define U64_MAX		((u64)~0ULL)
-#define S64_MAX		((s64)(U64_MAX >> 1))
-#define S64_MIN		((s64)(-S64_MAX - 1))
-
-#endif /* _LINUX_LIMITS_H */

include/linux/overflow.h

@@ -1,443 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 OR MIT */
-#ifndef __LINUX_OVERFLOW_H
-#define __LINUX_OVERFLOW_H
-
-#include <linux/compiler.h>
-#include <linux/limits.h>
-#include <linux/const.h>
-
-/*
- * We need to compute the minimum and maximum values representable in a given
- * type. These macros may also be useful elsewhere. It would seem more obvious
- * to do something like:
- *
- * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
- * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
- *
- * Unfortunately, the middle expressions, strictly speaking, have
- * undefined behaviour, and at least some versions of gcc warn about
- * the type_max expression (but not if -fsanitize=undefined is in
- * effect; in that case, the warning is deferred to runtime...).
- *
- * The slightly excessive casting in type_min is to make sure the
- * macros also produce sensible values for the exotic type _Bool. [The
- * overflow checkers only almost work for _Bool, but that's
- * a-feature-not-a-bug, since people shouldn't be doing arithmetic on
- * _Bools. Besides, the gcc builtins don't allow _Bool* as third
- * argument.]
- *
- * Idea stolen from
- * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html -
- * credit to Christian Biere.
- */
-#define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type)))
-#define __type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
-#define type_max(t)	__type_max(typeof(t))
-#define __type_min(T) ((T)((T)-type_max(T)-(T)1))
-#define type_min(t)	__type_min(typeof(t))
-
-/*
- * Avoids triggering -Wtype-limits compilation warning,
- * while using unsigned data types to check a < 0.
- */
-#define is_non_negative(a) ((a) > 0 || (a) == 0)
-#define is_negative(a) (!(is_non_negative(a)))
-
-/*
- * Allows for effectively applying __must_check to a macro so we can have
- * both the type-agnostic benefits of the macros while also being able to
- * enforce that the return value is, in fact, checked.
- */
-static inline bool __must_check __must_check_overflow(bool overflow)
-{
-	return unlikely(overflow);
-}
-
-/**
- * check_add_overflow() - Calculate addition with overflow checking
- * @a: first addend
- * @b: second addend
- * @d: pointer to store sum
- *
- * Returns true on wrap-around, false otherwise.
- *
- * *@d holds the results of the attempted addition, regardless of whether
- * wrap-around occurred.
- */
-#define check_add_overflow(a, b, d)	\
-	__must_check_overflow(__builtin_add_overflow(a, b, d))
-
-/**
- * wrapping_add() - Intentionally perform a wrapping addition
- * @type: type for result of calculation
- * @a: first addend
- * @b: second addend
- *
- * Return the potentially wrapped-around addition without
- * tripping any wrap-around sanitizers that may be enabled.
- */
-#define wrapping_add(type, a, b)				\
-	({							\
-		type __val;					\
-		__builtin_add_overflow(a, b, &__val);		\
-		__val;						\
-	})
-
-/**
- * wrapping_assign_add() - Intentionally perform a wrapping increment assignment
- * @var: variable to be incremented
- * @offset: amount to add
- *
- * Increments @var by @offset with wrap-around. Returns the resulting
- * value of @var. Will not trip any wrap-around sanitizers.
- *
- * Returns the new value of @var.
- */
-#define wrapping_assign_add(var, offset)				\
-	({								\
-		typeof(var) *__ptr = &(var);				\
-		*__ptr = wrapping_add(typeof(var), *__ptr, offset);	\
-	})
-
-/**
- * check_sub_overflow() - Calculate subtraction with overflow checking
- * @a: minuend; value to subtract from
- * @b: subtrahend; value to subtract from @a
- * @d: pointer to store difference
- *
- * Returns true on wrap-around, false otherwise.
- *
- * *@d holds the results of the attempted subtraction, regardless of whether
- * wrap-around occurred.
- */
-#define check_sub_overflow(a, b, d)	\
-	__must_check_overflow(__builtin_sub_overflow(a, b, d))
-
-/**
- * wrapping_sub() - Intentionally perform a wrapping subtraction
- * @type: type for result of calculation
- * @a: minuend; value to subtract from
- * @b: subtrahend; value to subtract from @a
- *
- * Return the potentially wrapped-around subtraction without
- * tripping any wrap-around sanitizers that may be enabled.
- */
-#define wrapping_sub(type, a, b)				\
-	({							\
-		type __val;					\
-		__builtin_sub_overflow(a, b, &__val);		\
-		__val;						\
-	})
-
-/**
- * wrapping_assign_sub() - Intentionally perform a wrapping decrement assign
- * @var: variable to be decremented
- * @offset: amount to subtract
- *
- * Decrements @var by @offset with wrap-around. Returns the resulting
- * value of @var. Will not trip any wrap-around sanitizers.
- *
- * Returns the new value of @var.
- */
-#define wrapping_assign_sub(var, offset)				\
-	({								\
-		typeof(var) *__ptr = &(var);				\
-		*__ptr = wrapping_sub(typeof(var), *__ptr, offset);	\
-	})
-
-/**
- * check_mul_overflow() - Calculate multiplication with overflow checking
- * @a: first factor
- * @b: second factor
- * @d: pointer to store product
- *
- * Returns true on wrap-around, false otherwise.
- *
- * *@d holds the results of the attempted multiplication, regardless of whether
- * wrap-around occurred.
- */
-#define check_mul_overflow(a, b, d)	\
-	__must_check_overflow(__builtin_mul_overflow(a, b, d))
-
-/**
- * wrapping_mul() - Intentionally perform a wrapping multiplication
- * @type: type for result of calculation
- * @a: first factor
- * @b: second factor
- *
- * Return the potentially wrapped-around multiplication without
- * tripping any wrap-around sanitizers that may be enabled.
- */
-#define wrapping_mul(type, a, b)				\
-	({							\
-		type __val;					\
-		__builtin_mul_overflow(a, b, &__val);		\
-		__val;						\
-	})
-
-/**
- * check_shl_overflow() - Calculate a left-shifted value and check overflow
- * @a: Value to be shifted
- * @s: How many bits left to shift
- * @d: Pointer to where to store the result
- *
- * Computes *@d = (@a << @s)
- *
- * Returns true if '*@d' cannot hold the result or when '@a << @s' doesn't
- * make sense. Example conditions:
- *
- * - '@a << @s' causes bits to be lost when stored in *@d.
- * - '@s' is garbage (e.g. negative) or so large that the result of
- *   '@a << @s' is guaranteed to be 0.
- * - '@a' is negative.
- * - '@a << @s' sets the sign bit, if any, in '*@d'.
- *
- * '*@d' will hold the results of the attempted shift, but is not
- * considered "safe for use" if true is returned.
- */
-#define check_shl_overflow(a, s, d) __must_check_overflow(({		\
-	typeof(a) _a = a;						\
-	typeof(s) _s = s;						\
-	typeof(d) _d = d;						\
-	unsigned long long _a_full = _a;				\
-	unsigned int _to_shift =					\
-		is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0;	\
-	*_d = (_a_full << _to_shift);					\
-	(_to_shift != _s || is_negative(*_d) || is_negative(_a) ||	\
-	(*_d >> _to_shift) != _a);					\
-}))
-
-#define __overflows_type_constexpr(x, T) (			\
-	is_unsigned_type(typeof(x)) ?				\
-		(x) > type_max(T) :				\
-	is_unsigned_type(typeof(T)) ?				\
-		(x) < 0 || (x) > type_max(T) :			\
-	(x) < type_min(T) || (x) > type_max(T))
-
-#define __overflows_type(x, T)		({	\
-	typeof(T) v = 0;			\
-	check_add_overflow((x), v, &v);		\
-})
-
-/**
- * overflows_type - helper for checking the overflows between value, variables,
- *		    or data type
- *
- * @n: source constant value or variable to be checked
- * @T: destination variable or data type proposed to store @x
- *
- * Compares the @x expression for whether or not it can safely fit in
- * the storage of the type in @T. @x and @T can have different types.
- * If @x is a constant expression, this will also resolve to a constant
- * expression.
- *
- * Returns: true if overflow can occur, false otherwise.
- */
-#define overflows_type(n, T)					\
-	__builtin_choose_expr(__is_constexpr(n),		\
-			      __overflows_type_constexpr(n, T),	\
-			      __overflows_type(n, T))
-
-/**
- * castable_to_type - like __same_type(), but also allows for casted literals
- *
- * @n: variable or constant value
- * @T: variable or data type
- *
- * Unlike the __same_type() macro, this allows a constant value as the
- * first argument. If this value would not overflow into an assignment
- * of the second argument's type, it returns true. Otherwise, this falls
- * back to __same_type().
- */
-#define castable_to_type(n, T)						\
-	__builtin_choose_expr(__is_constexpr(n),			\
-			      !__overflows_type_constexpr(n, T),	\
-			      __same_type(n, T))
-
-/**
- * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX
- * @factor1: first factor
- * @factor2: second factor
- *
- * 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 size_t __must_check size_mul(size_t factor1, size_t factor2)
-{
-	size_t bytes;
-
-	if (check_mul_overflow(factor1, factor2, &bytes))
-		return SIZE_MAX;
-
-	return bytes;
-}
-
-/**
- * size_add() - Calculate size_t addition with saturation at SIZE_MAX
- * @addend1: first addend
- * @addend2: second addend
- *
- * 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 size_t __must_check size_add(size_t addend1, size_t addend2)
-{
-	size_t bytes;
-
-	if (check_add_overflow(addend1, addend2, &bytes))
-		return SIZE_MAX;
-
-	return bytes;
-}
-
-/**
- * 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 size_t __must_check size_sub(size_t minuend, size_t subtrahend)
-{
-	size_t bytes;
-
-	if (minuend == SIZE_MAX || subtrahend == SIZE_MAX ||
-	    check_sub_overflow(minuend, subtrahend, &bytes))
-		return SIZE_MAX;
-
-	return bytes;
-}
-
-/**
- * array_size() - Calculate size of 2-dimensional array.
- * @a: dimension one
- * @b: dimension two
- *
- * Calculates size of 2-dimensional array: @a * @b.
- *
- * Returns: number of bytes needed to represent the array or SIZE_MAX on
- * overflow.
- */
-#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
- *                     within an enclosing structure.
- * @p: Pointer to the structure.
- * @member: Name of the flexible 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.
- *
- * Return: number of bytes needed or SIZE_MAX on overflow.
- */
-#define flex_array_size(p, member, count)				\
-	__builtin_choose_expr(__is_constexpr(count),			\
-		(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 of @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)					\
-	__builtin_choose_expr(__is_constexpr(count),			\
-		sizeof(*(p)) + flex_array_size(p, member, count),	\
-		size_add(sizeof(*(p)), flex_array_size(p, member, count)))
-
-/**
- * struct_size_t() - Calculate size of structure with trailing flexible array
- * @type: structure type name.
- * @member: Name of the array member.
- * @count: Number of elements in the array.
- *
- * Calculates size of memory needed for structure @type followed by an
- * array of @count number of @member elements. Prefer using struct_size()
- * when possible instead, to keep calculations associated with a specific
- * instance variable of type @type.
- *
- * Return: number of bytes needed or SIZE_MAX on overflow.
- */
-#define struct_size_t(type, member, count)					\
-	struct_size((type *)NULL, member, count)
-
-/**
- * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family.
- * Enables caller macro to pass (different) initializer.
- *
- * @type: structure type name, including "struct" keyword.
- * @name: Name for a variable to define.
- * @member: Name of the array member.
- * @count: Number of elements in the array; must be compile-time const.
- * @initializer: initializer expression (could be empty for no init).
- */
-#define _DEFINE_FLEX(type, name, member, count, initializer...)			\
-	_Static_assert(__builtin_constant_p(count),				\
-		       "onstack flex array members require compile-time const count"); \
-	union {									\
-		u8 bytes[struct_size_t(type, member, count)];			\
-		type obj;							\
-	} name##_u initializer;							\
-	type *name = (type *)&name##_u
-
-/**
- * DEFINE_RAW_FLEX() - Define an on-stack instance of structure with a trailing
- * flexible array member, when it does not have a __counted_by annotation.
- *
- * @type: structure type name, including "struct" keyword.
- * @name: Name for a variable to define.
- * @member: Name of the array member.
- * @count: Number of elements in the array; must be compile-time const.
- *
- * Define a zeroed, on-stack, instance of @type structure with a trailing
- * flexible array member.
- * Use __struct_size(@name) to get compile-time size of it afterwards.
- */
-#define DEFINE_RAW_FLEX(type, name, member, count)	\
-	_DEFINE_FLEX(type, name, member, count, = {})
-
-/**
- * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing
- * flexible array member.
- *
- * @TYPE: structure type name, including "struct" keyword.
- * @NAME: Name for a variable to define.
- * @MEMBER: Name of the array member.
- * @COUNTER: Name of the __counted_by member.
- * @COUNT: Number of elements in the array; must be compile-time const.
- *
- * Define a zeroed, on-stack, instance of @TYPE structure with a trailing
- * flexible array member.
- * Use __struct_size(@NAME) to get compile-time size of it afterwards.
- */
-#define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT)	\
-	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })
-
-#endif /* __LINUX_OVERFLOW_H */