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3080ea5553
There are many places where kernel code wants to have several different
typed trailing flexible arrays. This would normally be done with multiple
flexible arrays in a union, but since GCC and Clang don't (on the surface)
allow this, there have been many open-coded workarounds, usually involving
neighboring 0-element arrays at the end of a structure. For example,
instead of something like this:
struct thing {
...
union {
struct type1 foo[];
struct type2 bar[];
};
};
code works around the compiler with:
struct thing {
...
struct type1 foo[0];
struct type2 bar[];
};
Another case is when a flexible array is wanted as the single member
within a struct (which itself is usually in a union). For example, this
would be worked around as:
union many {
...
struct {
struct type3 baz[0];
};
};
These kinds of work-arounds cause problems with size checks against such
zero-element arrays (for example when building with -Warray-bounds and
-Wzero-length-bounds, and with the coming FORTIFY_SOURCE improvements),
so they must all be converted to "real" flexible arrays, avoiding warnings
like this:
fs/hpfs/anode.c: In function 'hpfs_add_sector_to_btree':
fs/hpfs/anode.c:209:27: warning: array subscript 0 is outside the bounds of an interior zero-length array 'struct bplus_internal_node[0]' [-Wzero-length-bounds]
209 | anode->btree.u.internal[0].down = cpu_to_le32(a);
| ~~~~~~~~~~~~~~~~~~~~~~~^~~
In file included from fs/hpfs/hpfs_fn.h:26,
from fs/hpfs/anode.c:10:
fs/hpfs/hpfs.h:412:32: note: while referencing 'internal'
412 | struct bplus_internal_node internal[0]; /* (internal) 2-word entries giving
| ^~~~~~~~
drivers/net/can/usb/etas_es58x/es58x_fd.c: In function 'es58x_fd_tx_can_msg':
drivers/net/can/usb/etas_es58x/es58x_fd.c:360:35: warning: array subscript 65535 is outside the bounds of an interior zero-length array 'u8[0]' {aka 'unsigned char[]'} [-Wzero-length-bounds]
360 | tx_can_msg = (typeof(tx_can_msg))&es58x_fd_urb_cmd->raw_msg[msg_len];
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from drivers/net/can/usb/etas_es58x/es58x_core.h:22,
from drivers/net/can/usb/etas_es58x/es58x_fd.c:17:
drivers/net/can/usb/etas_es58x/es58x_fd.h:231:6: note: while referencing 'raw_msg'
231 | u8 raw_msg[0];
| ^~~~~~~
However, it _is_ entirely possible to have one or more flexible arrays
in a struct or union: it just has to be in another struct. And since it
cannot be alone in a struct, such a struct must have at least 1 other
named member -- but that member can be zero sized. Wrap all this nonsense
into the new DECLARE_FLEX_ARRAY() in support of having flexible arrays
in unions (or alone in a struct).
As with struct_group(), since this is needed in UAPI headers as well,
implement the core there, with a non-UAPI wrapper.
Additionally update kernel-doc to understand its existence.
https://github.com/KSPP/linux/issues/137
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
100 lines
3.3 KiB
C
100 lines
3.3 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_STDDEF_H
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#define _LINUX_STDDEF_H
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#include <uapi/linux/stddef.h>
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#undef NULL
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#define NULL ((void *)0)
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enum {
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false = 0,
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true = 1
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};
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#undef offsetof
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#ifdef __compiler_offsetof
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#define offsetof(TYPE, MEMBER) __compiler_offsetof(TYPE, MEMBER)
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#else
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#define offsetof(TYPE, MEMBER) ((size_t)&((TYPE *)0)->MEMBER)
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#endif
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/**
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* sizeof_field() - Report the size of a struct field in bytes
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*
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* @TYPE: The structure containing the field of interest
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* @MEMBER: The field to return the size of
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*/
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#define sizeof_field(TYPE, MEMBER) sizeof((((TYPE *)0)->MEMBER))
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/**
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* offsetofend() - Report the offset of a struct field within the struct
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*
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* @TYPE: The type of the structure
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* @MEMBER: The member within the structure to get the end offset of
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*/
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#define offsetofend(TYPE, MEMBER) \
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(offsetof(TYPE, MEMBER) + sizeof_field(TYPE, MEMBER))
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/**
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* struct_group() - Wrap a set of declarations in a mirrored struct
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*
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* @NAME: The identifier name of the mirrored sub-struct
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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
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* layout and size: one anonymous and one named. The former can be
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* used normally without sub-struct naming, and the latter can be
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* used to reason about the start, end, and size of the group of
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* struct members.
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*/
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#define struct_group(NAME, MEMBERS...) \
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__struct_group(/* no tag */, NAME, /* no attrs */, MEMBERS)
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/**
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* struct_group_attr() - Create a struct_group() with trailing attributes
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*
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* @NAME: The identifier name of the mirrored sub-struct
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* @ATTRS: Any struct attributes to apply
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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
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* layout and size: one anonymous and one named. The former can be
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* used normally without sub-struct naming, and the latter can be
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* used to reason about the start, end, and size of the group of
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* struct members. Includes structure attributes argument.
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*/
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#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
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__struct_group(/* no tag */, NAME, ATTRS, MEMBERS)
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/**
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* struct_group_tagged() - Create a struct_group with a reusable tag
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*
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* @TAG: The tag name for the named sub-struct
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* @NAME: The identifier name of the mirrored sub-struct
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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
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* layout and size: one anonymous and one named. The former can be
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* used normally without sub-struct naming, and the latter can be
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* used to reason about the start, end, and size of the group of
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* struct members. Includes struct tag argument for the named copy,
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* so the specified layout can be reused later.
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*/
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#define struct_group_tagged(TAG, NAME, MEMBERS...) \
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__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
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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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__DECLARE_FLEX_ARRAY(TYPE, NAME)
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#endif
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