linux-kernel - Re: [PATCH 16/32] staging: gasket: always allow root open for write

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Date:   Thu, 19 Jul 2018 16:47:17 -0700
From:   Todd Poynor <toddpoynor@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Rob Springer <rspringer@...gle.com>,
        John Joseph <jnjoseph@...gle.com>,
        Ben Chan <benchan@...omium.org>,
        Zhongze Hu <frankhu@...omium.org>,
        Simon Que <sque@...omium.org>,
        Dmitry Torokhov <dtor@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        devel@...verdev.osuosl.org, lkml <linux-kernel@...r.kernel.org>,
        Todd Poynor <toddpoynor@...gle.com>
Subject: Re: [PATCH 16/32] staging: gasket: always allow root open for write

On Thu, Jul 19, 2018 at 2:29 AM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> On Tue, Jul 17, 2018 at 01:56:56PM -0700, Todd Poynor wrote:
>> From: Todd Poynor <toddpoynor@...gle.com>
>>
>> Always allow root to open device for writing.
>>
>> Drop special-casing of ioctl permissions for root vs. owner.
>>
>> Reported-by: Dmitry Torokhov <dtor@...omium.org>
>> Signed-off-by: Zhongze Hu <frankhu@...omium.org>
>> Signed-off-by: Todd Poynor <toddpoynor@...gle.com>
>> ---
>>  drivers/staging/gasket/apex_driver.c  |  9 +--------
>>  drivers/staging/gasket/gasket_core.c  |  8 +++++---
>>  drivers/staging/gasket/gasket_ioctl.c | 19 ++++++++-----------
>>  3 files changed, 14 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/staging/gasket/apex_driver.c b/drivers/staging/gasket/apex_driver.c
>> index 3a83c3d4d5561..612b3ab803196 100644
>> --- a/drivers/staging/gasket/apex_driver.c
>> +++ b/drivers/staging/gasket/apex_driver.c
>> @@ -629,14 +629,7 @@ static bool is_gcb_in_reset(struct gasket_dev *gasket_dev)
>>   */
>>  static uint apex_ioctl_check_permissions(struct file *filp, uint cmd)
>>  {
>> -     struct gasket_dev *gasket_dev = filp->private_data;
>> -     int root = capable(CAP_SYS_ADMIN);
>> -     int is_owner = gasket_dev->dev_info.ownership.is_owned &&
>> -                    current->tgid == gasket_dev->dev_info.ownership.owner;
>> -
>> -     if (root || is_owner)
>> -             return 1;
>> -     return 0;
>> +     return !!(filp->f_mode & FMODE_WRITE);
>
> Shouldn't this return a boolean instead of uint?

There's a patch farther down in the stack that does that, I wasn't
sure if I should collapse the two things together into a single patch,
will fold that patch into this one.

>
>>  }
>>
>>  /*
>> diff --git a/drivers/staging/gasket/gasket_core.c b/drivers/staging/gasket/gasket_core.c
>> index 0d5ba7359af73..947b4fcc76970 100644
>> --- a/drivers/staging/gasket/gasket_core.c
>> +++ b/drivers/staging/gasket/gasket_core.c
>> @@ -1085,6 +1085,7 @@ static int gasket_open(struct inode *inode, struct file *filp)
>>       char task_name[TASK_COMM_LEN];
>>       struct gasket_cdev_info *dev_info =
>>           container_of(inode->i_cdev, struct gasket_cdev_info, cdev);
>> +     int is_root = capable(CAP_SYS_ADMIN);
>>
>>       gasket_dev = dev_info->gasket_dev_ptr;
>>       driver_desc = gasket_dev->internal_desc->driver_desc;
>> @@ -1098,7 +1099,7 @@ static int gasket_open(struct inode *inode, struct file *filp)
>>               "Attempting to open with tgid %u (%s) (f_mode: 0%03o, "
>>               "fmode_write: %d is_root: %u)",
>>               current->tgid, task_name, filp->f_mode,
>> -             (filp->f_mode & FMODE_WRITE), capable(CAP_SYS_ADMIN));
>> +             (filp->f_mode & FMODE_WRITE), is_root);
>>
>>       /* Always allow non-writing accesses. */
>>       if (!(filp->f_mode & FMODE_WRITE)) {
>> @@ -1112,8 +1113,9 @@ static int gasket_open(struct inode *inode, struct file *filp)
>>               gasket_dev, "Current owner open count (owning tgid %u): %d.",
>>               ownership->owner, ownership->write_open_count);
>>
>> -     /* Opening a node owned by another TGID is an error (even root.) */
>> -     if (ownership->is_owned && ownership->owner != current->tgid) {
>> +     /* Opening a node owned by another TGID is an error (unless root) */
>> +     if (ownership->is_owned && ownership->owner != current->tgid &&
>> +         !is_root) {
>>               gasket_log_error(
>>                       gasket_dev,
>>                       "Process %u is opening a node held by %u.",
>> diff --git a/drivers/staging/gasket/gasket_ioctl.c b/drivers/staging/gasket/gasket_ioctl.c
>> index 0c2f85cf54480..d0fa05b8bf1d3 100644
>> --- a/drivers/staging/gasket/gasket_ioctl.c
>> +++ b/drivers/staging/gasket/gasket_ioctl.c
>> @@ -171,7 +171,7 @@ long gasket_is_supported_ioctl(uint cmd)
>>   */
>>  static uint gasket_ioctl_check_permissions(struct file *filp, uint cmd)
>>  {
>
> Also return bool?

Will fix, I had meant to send a patch for this, will just do that here.

>
>> -     uint alive, root, device_owner;
>> +     uint alive;
>>       fmode_t read, write;
>>       struct gasket_dev *gasket_dev = (struct gasket_dev *)filp->private_data;
>>
>> @@ -183,33 +183,30 @@ static uint gasket_ioctl_check_permissions(struct file *filp, uint cmd)
>>                       alive, gasket_dev->status);
>>       }
>>
>> -     root = capable(CAP_SYS_ADMIN);
>> -     read = filp->f_mode & FMODE_READ;
>> -     write = filp->f_mode & FMODE_WRITE;
>> -     device_owner = (gasket_dev->dev_info.ownership.is_owned &&
>> -                     current->tgid == gasket_dev->dev_info.ownership.owner);
>> +     read = !!(filp->f_mode & FMODE_READ);
>> +     write = !!(filp->f_mode & FMODE_WRITE);
>
> These should be bool as well, right?

Right.

>
> I'll drop this patch, thanks.
>
> greg k-h



-- 
Todd