From: Jiri Slaby <jslaby@suse.com>
To: "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tty: n_hdlc: Use flexible-array member
Date: Tue, 21 Jan 2020 06:54:22 +0100 [thread overview]
Message-ID: <a1bfbaaf-7a96-ab44-85fd-1bb8b4e6b06f@suse.com> (raw)
In-Reply-To: <20200120234528.GA26790@embeddedor.com>
On 21. 01. 20, 0:45, Gustavo A. R. Silva wrote:
> Old code in the kernel uses 1-byte and 0-byte arrays to indicate the
> presence of a "variable length array":
>
> struct something {
> int length;
> u8 data[1];
> };
>
> struct something *instance;
>
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
>
> There is also 0-byte arrays. Both cases pose confusion for things like
> sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism
> to declare variable-length types such as the one above is a flexible array
> member[2] which need to be the last member of a structure and empty-sized:
>
> struct something {
> int stuff;
> u8 data[];
> };
>
> Also, by making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure, which
> will help us prevent some kind of undefined behavior bugs from being
> unadvertenly introduced[3] to the codebase from now on.
>
> [1] https://github.com/KSPP/linux/issues/21
> [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> ---
> drivers/tty/n_hdlc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c
> index 98361acd3053..b5499ca8757e 100644
> --- a/drivers/tty/n_hdlc.c
> +++ b/drivers/tty/n_hdlc.c
> @@ -115,7 +115,7 @@
> struct n_hdlc_buf {
> struct list_head list_item;
> int count;
> - char buf[1];
> + char buf[];
> };
>
> #define N_HDLC_BUF_SIZE (sizeof(struct n_hdlc_buf) + maxframe)
Have you checked, that you don't have to "+ 1" here now?
Other than that:
Acked-by: Jiri Slaby <jslaby@suse.cz>
thanks,
--
js
suse labs
next prev parent reply other threads:[~2020-01-21 5:54 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-20 23:45 [PATCH] tty: n_hdlc: Use flexible-array member Gustavo A. R. Silva
2020-01-21 5:54 ` Jiri Slaby [this message]
2020-01-21 14:27 ` Gustavo A. R. Silva
2020-01-21 15:00 ` Mikael Magnusson
2020-01-21 15:14 ` Gustavo A. R. Silva
2020-01-21 15:24 ` Gustavo A. R. Silva
2020-01-21 16:03 ` Gustavo A. R. Silva
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