27b581d460
[ Upstream commit 32a4ec211d4164e667d9d0b807fadf02053cd2e9 ]
__DECLARE_FLEX_ARRAY(T, member) macro expands to
struct {
struct {} __empty_member;
T member[];
};
which is subtly wrong in C++ because sizeof(struct{}) is 1 not 0,
changing UAPI structures layouts.
This can be fixed by expanding to
T member[];
Now g++ doesn't like "T member[]" either, throwing errors on
the following code:
struct S {
union {
T1 member1[];
T2 member2[];
};
};
or
struct S {
T member[];
};
Use "T member[0];" which seems to work and does the right thing wrt
structure layout.
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Fixes: 3080ea5553cc ("stddef: Introduce DECLARE_FLEX_ARRAY() helper")
Link: https://lore.kernel.org/r/97242381-f1ec-4a4a-9472-1a464f575657@p183
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
54 lines
1.7 KiB
C
Executable file
54 lines
1.7 KiB
C
Executable file
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef _UAPI_LINUX_STDDEF_H
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#define _UAPI_LINUX_STDDEF_H
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#include <linux/compiler_types.h>
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#ifndef __always_inline
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#define __always_inline inline
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#endif
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/**
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* __struct_group() - Create a mirrored named and anonyomous struct
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*
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* @TAG: The tag name for the named sub-struct (usually empty)
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* @NAME: The identifier name of the mirrored sub-struct
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* @ATTRS: Any struct attributes (usually empty)
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* @MEMBERS: The member declarations for the mirrored structs
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*
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* Used to create an anonymous union of two structs with identical layout
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* and size: one anonymous and one named. The former's members can be used
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* normally without sub-struct naming, and the latter can be used to
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* reason about the start, end, and size of the group of struct members.
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* The named struct can also be explicitly tagged for layer reuse, as well
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* as both having struct attributes appended.
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*/
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#define __struct_group(TAG, NAME, ATTRS, MEMBERS...) \
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union { \
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struct { MEMBERS } ATTRS; \
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struct TAG { MEMBERS } ATTRS NAME; \
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}
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#ifdef __cplusplus
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/* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */
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#define __DECLARE_FLEX_ARRAY(T, member) \
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T member[0]
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#else
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/**
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* __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
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*
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* @TYPE: The type of each flexible array element
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* @NAME: The name of the flexible array member
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*
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* In order to have a flexible array member in a union or alone in a
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* struct, it needs to be wrapped in an anonymous struct with at least 1
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* named member, but that member can be empty.
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*/
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#define __DECLARE_FLEX_ARRAY(TYPE, NAME) \
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struct { \
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struct { } __empty_ ## NAME; \
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TYPE NAME[]; \
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}
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#endif
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#endif
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