mirror of
https://github.com/torvalds/linux.git
synced 2024-11-23 12:42:02 +00:00
ffbc93768e
Hi Linus,
Please, pull the following patches that replace zero-length arrays with
flexible-array members.
Notice that all of these patches have been baking in linux-next for
two development cycles now.
There is a regular need in the kernel to provide a way to declare having a
dynamically sized set of trailing elements in a structure. Kernel code should
always use “flexible array members”[1] for these cases. The older style of
one-element or zero-length arrays should no longer be used[2].
C99 introduced “flexible array members”, which lacks a numeric size for the
array declaration entirely:
struct something {
size_t count;
struct foo items[];
};
This is the way the kernel expects dynamically sized trailing elements to be
declared. It allows the compiler to generate errors when the flexible array
does not occur last in the structure, which helps to prevent some kind of
undefined behavior[3] bugs from being inadvertently introduced to the codebase.
It also allows the compiler to correctly analyze array sizes (via sizeof(),
CONFIG_FORTIFY_SOURCE, and CONFIG_UBSAN_BOUNDS). For instance, there is no
mechanism that warns us that the following application of the sizeof() operator
to a zero-length array always results in zero:
struct something {
size_t count;
struct foo items[0];
};
struct something *instance;
instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
instance->count = count;
size = sizeof(instance->items) * instance->count;
memcpy(instance->items, source, size);
At the last line of code above, size turns out to be zero, when one might have
thought it represents the total size in bytes of the dynamic memory recently
allocated for the trailing array items. Here are a couple examples of this
issue[4][5]. Instead, flexible array members have incomplete type, and so the
sizeof() operator may not be applied[6], so any misuse of such operators will
be immediately noticed at build time.
The cleanest and least error-prone way to implement this is through the use of
a flexible array member:
struct something {
size_t count;
struct foo items[];
};
struct something *instance;
instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
instance->count = count;
size = sizeof(instance->items[0]) * instance->count;
memcpy(instance->items, source, size);
Thanks
--
Gustavo
[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/21
[3] https://git.kernel.org/linus/76497732932f15e7323dc805e8ea8dc11bb587cf
[4] https://git.kernel.org/linus/f2cd32a443da694ac4e28fbf4ac6f9d5cc63a539
[5] https://git.kernel.org/linus/ab91c2a89f86be2898cee208d492816ec238b2cf
[6] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
-----BEGIN PGP SIGNATURE-----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=8HUQ
-----END PGP SIGNATURE-----
Merge tag 'flex-array-conversions-5.8-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux
Pull flexible-array member conversions from Gustavo A. R. Silva:
"Replace zero-length arrays with flexible-array members.
Notice that all of these patches have been baking in linux-next for
two development cycles now.
There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should no
longer be used[2].
C99 introduced “flexible array members”, which lacks a numeric size
for the array declaration entirely:
struct something {
size_t count;
struct foo items[];
};
This is the way the kernel expects dynamically sized trailing elements
to be declared. It allows the compiler to generate errors when the
flexible array does not occur last in the structure, which helps to
prevent some kind of undefined behavior[3] bugs from being
inadvertently introduced to the codebase.
It also allows the compiler to correctly analyze array sizes (via
sizeof(), CONFIG_FORTIFY_SOURCE, and CONFIG_UBSAN_BOUNDS). For
instance, there is no mechanism that warns us that the following
application of the sizeof() operator to a zero-length array always
results in zero:
struct something {
size_t count;
struct foo items[0];
};
struct something *instance;
instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
instance->count = count;
size = sizeof(instance->items) * instance->count;
memcpy(instance->items, source, size);
At the last line of code above, size turns out to be zero, when one
might have thought it represents the total size in bytes of the
dynamic memory recently allocated for the trailing array items. Here
are a couple examples of this issue[4][5].
Instead, flexible array members have incomplete type, and so the
sizeof() operator may not be applied[6], so any misuse of such
operators will be immediately noticed at build time.
The cleanest and least error-prone way to implement this is through
the use of a flexible array member:
struct something {
size_t count;
struct foo items[];
};
struct something *instance;
instance = kmalloc(struct_size(instance, items, count), GFP_KERNEL);
instance->count = count;
size = sizeof(instance->items[0]) * instance->count;
memcpy(instance->items, source, size);
instead"
[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://github.com/KSPP/linux/issues/21
[3] commit
|
||
|---|---|---|
| .. | ||
| alpha | ||
| arc | ||
| arm | ||
| arm64 | ||
| c6x | ||
| csky | ||
| h8300 | ||
| hexagon | ||
| ia64 | ||
| m68k | ||
| microblaze | ||
| mips | ||
| nds32 | ||
| nios2 | ||
| openrisc | ||
| parisc | ||
| powerpc | ||
| riscv | ||
| s390 | ||
| sh | ||
| sparc | ||
| um | ||
| unicore32 | ||
| x86 | ||
| xtensa | ||
| .gitignore | ||
| Kconfig | ||