netdev - Re: [PATCH net] devlink: uninitialized data in nsim_dev_trap_fa_cookie

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Message-ID: <CALs4sv15dEWv99r0b8YqjVGJL+=76dhWBK38S-u-=_wy3QovYA@mail.gmail.com>
Date: Wed, 12 Jul 2023 10:59:08 +0530
From: Pavan Chebbi <pavan.chebbi@...adcom.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Jiri Pirko <jiri@...nulli.us>, Jakub Kicinski <kuba@...nel.org>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Paolo Abeni <pabeni@...hat.com>, Ido Schimmel <idosch@...lanox.com>, netdev@...r.kernel.org, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH net] devlink: uninitialized data in nsim_dev_trap_fa_cookie_write()

On Tue, Jul 11, 2023 at 2:22 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> The simple_write_to_buffer() function is designed to handle partial
> writes.  It returns negatives on error, otherwise it returns the number
> of bytes that were able to be copied.  This code doesn't check the
> return properly.  We only know that the first byte is written, the rest
> of the buffer might be uninitialized.
>
> There is no need to use the simple_write_to_buffer() function.
> Partial writes are prohibited by the "if (*ppos != 0)" check at the
> start of the function.  Just use memdup_user() and copy the whole
> buffer.
>
> Fixes: d3cbb907ae57 ("netdevsim: add ACL trap reporting cookie as a metadata")
> Signed-off-by: Dan Carpenter <dan.carpenter@...aro.org>
> ---
>  drivers/net/netdevsim/dev.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
> index 6045bece2654..b4d3b9cde8bd 100644
> --- a/drivers/net/netdevsim/dev.c
> +++ b/drivers/net/netdevsim/dev.c
> @@ -184,13 +184,10 @@ static ssize_t nsim_dev_trap_fa_cookie_write(struct file *file,
>         cookie_len = (count - 1) / 2;
>         if ((count - 1) % 2)
>                 return -EINVAL;
> -       buf = kmalloc(count, GFP_KERNEL | __GFP_NOWARN);
> -       if (!buf)
> -               return -ENOMEM;
>
> -       ret = simple_write_to_buffer(buf, count, ppos, data, count);
> -       if (ret < 0)
> -               goto free_buf;
> +       buf = memdup_user(data, count);

Looks good to me except that now memory comes from GFP_USER.
Within limits it still looks all fine to me.
Reviewed-by: Pavan Chebbi <pavan.chebbi@...adcom.com>


> +       if (IS_ERR(buf))
> +               return PTR_ERR(buf);
>
>         fa_cookie = kmalloc(sizeof(*fa_cookie) + cookie_len,
>                             GFP_KERNEL | __GFP_NOWARN);
> --
> 2.39.2
>
>

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