linux-kernel - Re: [PATCH] cifs: Replace one-element array with flexible-array member

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Message-ID: <CAN05THS5A5r8PgaHk8BaK+8kTyT8mJ3LdB__tJCbSb8Cs+yaKQ@mail.gmail.com>
Date:   Tue, 18 Jan 2022 07:01:23 +1000
From:   ronnie sahlberg <ronniesahlberg@...il.com>
To:     cgel.zte@...il.com
Cc:     Steve French <sfrench@...ba.org>,
        linux-cifs <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Changcheng Deng <deng.changcheng@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] cifs: Replace one-element array with flexible-array member

This patch is wrong.
qi_iov is not even the trailing element of the array so we cant change
it to be a flexible array member.
This change will likely clobber io_iov so the potential for breaking,
memory leaks or ooops is quite possible.
qi_iov is supposed to be exactly one element in size.

Same for close_iov, while it is the last element in the structure, it
is not a flexible array but an array of exactly one member.
This change to close_iov would likely lead to reading/writing beyond
the end of the structure.


NACK

On Sat, Jan 15, 2022 at 12:44 AM <cgel.zte@...il.com> wrote:
>
> From: Changcheng Deng <deng.changcheng@....com.cn>
>
> 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" for these cases. The older
> style of one-element or zero-length arrays should no longer be used.
> Reference:
> https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays
>
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Changcheng Deng <deng.changcheng@....com.cn>
> ---
>  fs/cifs/smb2ops.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index af5d0830bc8a..5c104b2f308a 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -1609,10 +1609,10 @@ struct iqi_vars {
>         struct smb_rqst rqst[3];
>         struct kvec rsp_iov[3];
>         struct kvec open_iov[SMB2_CREATE_IOV_SIZE];
> -       struct kvec qi_iov[1];
> +       struct kvec qi_iov[];
>         struct kvec io_iov[SMB2_IOCTL_IOV_SIZE];
>         struct kvec si_iov[SMB2_SET_INFO_IOV_SIZE];
> -       struct kvec close_iov[1];
> +       struct kvec close_iov[];
>  };
>
>  static int
> --
> 2.25.1
>