linux-kernel - Re: [PATCH v1 1/2] fsi: sbefifo: Remove write's max command length

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Date:   Mon, 11 Sep 2023 06:03:49 +0000
From:   Joel Stanley <joel@....id.au>
To:     Ninad Palsule <ninad@...ux.ibm.com>
Cc:     jk@...abs.org, alistair@...ple.id.au, eajames@...ux.ibm.com,
        linux-fsi@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/2] fsi: sbefifo: Remove write's max command length

On Thu, 7 Sept 2023 at 22:10, Ninad Palsule <ninad@...ux.ibm.com> wrote:
>
> This commit removes max command length check in the user write path.
> This is required to support images larger than 1MB. This should not
> create any issues as read path does not have this check either.
>
> As per the original design cronus server was suppose to break up the
> image into 1MB pieces but it requires restructuring of the driver.

When you say "driver" you mean the kernel driver, or userspace?

This isn't a great justification for removing a bounds check.

> Today driver sends EOT message on each write request so we will have to
> send it only after all pieces are sent which requires large change hence
> we decided to remove this check.

This paragraph could be clearer. Could you try rephrasing?

Assuming we want to make this change, what is the expected maximum
transfer? Could we instead make the check be that value (3MB?).

>
> Testing:
>   Loaded 3 MB image through cronus server.
>
> Signed-off-by: Ninad Palsule <ninad@...ux.ibm.com>
> ---
>  drivers/fsi/fsi-sbefifo.c | 3 ---
>  1 file changed, 3 deletions(-)
>
> diff --git a/drivers/fsi/fsi-sbefifo.c b/drivers/fsi/fsi-sbefifo.c
> index 9912b7a6a4b9..b771dff27f7f 100644
> --- a/drivers/fsi/fsi-sbefifo.c
> +++ b/drivers/fsi/fsi-sbefifo.c
> @@ -113,7 +113,6 @@ enum sbe_state
>  #define SBEFIFO_TIMEOUT_IN_RSP         1000
>
>  /* Other constants */
> -#define SBEFIFO_MAX_USER_CMD_LEN       (0x100000 + PAGE_SIZE)
>  #define SBEFIFO_RESET_MAGIC            0x52534554 /* "RSET" */
>
>  struct sbefifo {
> @@ -870,8 +869,6 @@ static ssize_t sbefifo_user_write(struct file *file, const char __user *buf,
>         if (!user)
>                 return -EINVAL;
>         sbefifo = user->sbefifo;
> -       if (len > SBEFIFO_MAX_USER_CMD_LEN)
> -               return -EINVAL;
>         if (len & 3)
>                 return -EINVAL;
>
> --
> 2.39.2
>