Hi Denis,
Thanks a lot for working on this. Please, see some comments below...
On 8/6/20 17:03, Denis Efremov wrote:
> Commit 68e4cd17e218 ("docs: deprecated.rst: Add zero-length and one-element
> arrays") marks one-element and zero-length arrays as deprecated. Kernel
> code should always use "flexible array members" instead.
>
> The script warns about one-element and zero-length arrays in structs.
>
> Cc: Kees Cook
> Cc: Gustavo A. R. Silva
> Signed-off-by: Denis Efremov
> ---
>
> Currently, it's just a draft. I've placed a number of questions in the
> script and marked them as TODO. Kees, Gustavo, if you could help me with
> my questions I think that this rule will be enough to close:
> https://github.com/KSPP/linux/issues/76
>
> BTW, I it's possible to not warn about files in uapi folder if
> this is relevant. Do I need to do it in the script?
>
I think the script should warn about new additions of zero-length/one-element
arrays in UAPI.
> scripts/coccinelle/misc/flexible_array.cocci | 158 +++
> 1 file changed, 158 insertions(+)
> create mode 100644 scripts/coccinelle/misc/flexible_array.cocci
>
> diff --git a/scripts/coccinelle/misc/flexible_array.cocci
> b/scripts/coccinelle/misc/flexible_array.cocci
> new file mode 100644
> index ..1e7165c79e60
> --- /dev/null
> +++ b/scripts/coccinelle/misc/flexible_array.cocci
> @@ -0,0 +1,158 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +///
> +/// Zero-length and one-element arrays are deprecated, see
> +/// Documentation/process/deprecated.rst
> +/// Flexible-array members should be used instead.
> +///
> +//
> +// Confidence: High
> +// Copyright: (C) 2020 Denis Efremov ISPRAS.
> +// Comments:
> +// Options: --no-includes --include-headers
> +
> +virtual context
> +virtual report
> +virtual org
> +virtual patch
> +
> +@r depends on !patch@
> +identifier name, size, array;
> +// TODO: We can additionally restrict size and array to:
> +// identifier size =~ ".*(num|len|count|size|ncpus).*";
> +// identifier array !~ ".*(pad|reserved).*";
> +// Do we need it?
> +type TS, TA;
> +position p;
> +@@
> +
> +(
> + // This will also match: typedef struct name { ...
> + // However nested structs are not matched, i.e.:
> + // struct name1 { struct name2 { int s; int a[0]; } st; int i; }
> + // will not be matched. Do we need to handle it?
It's fine. I think this would be a different script. One that
exclusively look for all three: zero-length, one-element arrays
and flexible array members in nested structures because
"A structure containing a flexible array member, or a union
containing such a structure (possibly recursively), may not be
a member of a structure or an element of an array. (However
these uses are permitted by GCC as extensions.)"[1]
> + struct name {
> +... // TODO: Maybe simple ... is enough? It will match structs with
> a
Yep; simple is always better at first. :)
> +TS size; // single field, e.g.
> +... //
> https://elixir.bootlin.com/linux/v5.8/source/arch/arm/include/uapi/asm/setup.h#L127
> +(
> +*TA array@p[0];
> +|
> + // TODO: It seems that there are exception cases for array[1], e.g.
> + //
> https://elixir.bootlin.com/linux/v5.8/source/arch/powerpc/boot/rs6000.h#L152
> + //
> https://elixir.bootlin.com/linux/v5.8/source/include/uapi/linux/cdrom.h#L292
> + //
> https://elixir.bootlin.com/linux/v5.8/source/drivers/net/wireless/ath/ath6kl/usb.c#L108
> + // We could either drop array[1] checking from this rule or
> + // restrict array name with regexp and add, for example, an "allowlist"
> + // with struct names where we allow this code pattern.
> + // TODO: How to handle: u8 data[1][MAXLEN_PSTR6]; ?
> +*TA array@p[1];
> +)
> + };
> +|
> + struct {
> +...
> +TS size;
> +...
> +(
> +*TA array@p[0];
> +|
> +*TA array@p[1];
> +)
> + };
> +|
> + // TODO: do we need to handle unions?
Yep; we should warn about this in unions, too.
However, I think unions cannot have members with
incomplete type, so we should not suggest the use
of flexible-array members in unions, because
flexible arrays have incomplete type.
> + union name {
> +...
> +TS size;
> +...
> +(
> +*TA array@p[0];
> +|
> +*TA array@p[1];
> +)
> + };
> +|
> + union {
> +...
> +TS size;
> +...
> +(
> +*TA array@p[0];
> +|
> +*TA array@p[1];
> +)
> + };
> +)
> +
> +// FIXME: Patch mode doesn't work as expected.
> +// Coccinelle handles formatting incorrectly.
> +// Patch mode in this rule should be disabled until
> +// proper formatting will be supported.
> +@depends on patch exists@
> +identifier name, size, array;
> +type TS, TA;
> +@@
> +
> +(
> + struct name {
> +...
> +TS size;
> +...
> +(
> +-TA array[0];
> +|
> +-TA array[1];
> +)
> ++TA array[];
> + };
> +|
> + struct {
> +...
> +TS size;
> +...
> +(
> +-TA array[0];
> +|
> +-TA array[1];
> +)
> ++
