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From:   adam radford <aradford@gmail.com>
Date:   Mon, 7 May 2018 17:31:27 -0700
Message-ID: <CAHtARFFcrKnCtaH8hSLEFnia_pphL8UJ24Oxy=_r77fPRq5j0Q@mail.gmail.com>
Subject: Re: [PATCH] scsi: 3w-xxxx: fix a missing-check bug
To:     Wenwen Wang <wang6495@umn.edu>
Cc:     Kangjie Lu <kjlu@umn.edu>,
        "James E.J. Bottomley" <jejb@linux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        linux-scsi <linux-scsi@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
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On Sat, May 5, 2018 at 10:48 PM, Wenwen Wang <wang6495@umn.edu> wrote:
> In tw_chrdev_ioctl(), the length of the data buffer is firstly copied from
> the userspace pointer 'argp' and saved to the kernel object
> 'data_buffer_length'. Then a security check is performed on it to make sure
> that the length is not more than 'TW_MAX_IOCTL_SECTORS * 512'. Otherwise,
> an error code -EINVAL is returned. If the security check is passed, the
> entire ioctl command is copied again from the 'argp' pointer and saved to
> the kernel object 'tw_ioctl'. Then, various operations are performed on
> 'tw_ioctl' according to the 'cmd'. Given that the 'argp' pointer resides in
> userspace, a malicious userspace process can race to change the buffer
> length between the two copies. This way, the user can bypass the security
> check and inject invalid data buffer length. This can cause potential
> security issues in the following execution.
>
> This patch checks the buffer length obtained in the second copy. An error
> code -EINVAL will be returned if it is not same as the original one in the
> first copy.
>
> Signed-off-by: Wenwen Wang <wang6495@umn.edu>
> ---
>  drivers/scsi/3w-xxxx.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/scsi/3w-xxxx.c b/drivers/scsi/3w-xxxx.c
> index 33261b6..ef79194 100644
> --- a/drivers/scsi/3w-xxxx.c
> +++ b/drivers/scsi/3w-xxxx.c
> @@ -919,6 +919,10 @@ static long tw_chrdev_ioctl(struct file *file, unsigned int cmd, unsigned long a
>         /* Now copy down the entire ioctl */
>         if (copy_from_user(tw_ioctl, argp, data_buffer_length + sizeof(TW_New_Ioctl) - 1))
>                 goto out2;
> +       if (tw_ioctl->data_buffer_length != data_buffer_length) {
> +               retval = -EINVAL;
> +               goto out2;
> +       }
>
>         passthru = (TW_Passthru *)&tw_ioctl->firmware_command;
>
> --
> 2.7.4
>

I would drop this patch and check for !capable(CAP_SYS_ADMIN) in
tw_chrdev_open() instead.

-Adam