lkml.org 
[lkml]   [2020]   [May]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] debugfs: Add mount restriction option
Date
On 5/28/20 2:23 PM, Greg Kroah-Hartman wrote:
> On Thu, May 28, 2020 at 12:04:32PM +0000, Enderborg, Peter wrote:
>> On 5/28/20 11:27 AM, Greg Kroah-Hartman wrote:
>>> On Thu, May 28, 2020 at 08:39:02AM +0000, Enderborg, Peter wrote:
>>>> On 5/28/20 10:27 AM, Greg Kroah-Hartman wrote:
>>>>> On Thu, May 28, 2020 at 10:00:31AM +0200, Peter Enderborg wrote:
>>>>>> Since debugfs include sensitive information it need to be treated
>>>>>> carefully. But it also has many very useful debug functions for userspace.
>>>>>> With this option we can have same configuration for system with
>>>>>> need of debugfs and a way to turn it off. It is needed new
>>>>>> kernel command line parameter to be activated.
>>>>> By "configuration" do you mean "kernel configuration"? What is wrong
>>>>> with relying on the build option like we do today?
>>>>>
>>>>> You might want to reword all of this to make more sense about the
>>>>> "problem" you are trying to solve here, as I don't really understand it,
>>>>> sorry.
>>>>>
>>>>>
>>>>>> Signed-off-by: Peter Enderborg <peter.enderborg@sony.com>
>>>>>> ---
>>>>>> fs/debugfs/inode.c | 17 ++++++++++++++++-
>>>>>> lib/Kconfig.debug | 10 ++++++++++
>>>>>> 2 files changed, 26 insertions(+), 1 deletion(-)
>>>>> No documentation update? That's not good :(
>>>>>
>>>>>
>>>>>> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
>>>>>> index b7f2e971ecbc..bde37dab77e0 100644
>>>>>> --- a/fs/debugfs/inode.c
>>>>>> +++ b/fs/debugfs/inode.c
>>>>>> @@ -786,10 +786,25 @@ bool debugfs_initialized(void)
>>>>>> }
>>>>>> EXPORT_SYMBOL_GPL(debugfs_initialized);
>>>>>>
>>>>>> +static int allow_debugfs;
>>>>>> +
>>>>>> +static int __init debugfs_kernel(char *str)
>>>>>> +{
>>>>>> + if (str && !strcmp(str, "true"))
>>>>>> + allow_debugfs = true;
>>>>>> +
>>>>>> + return 0;
>>>>>> +
>>>>>> +}
>>>>>> +early_param("debugfs", debugfs_kernel);
>>>>>> +
>>>>>> static int __init debugfs_init(void)
>>>>>> {
>>>>>> int retval;
>>>>>> -
>>>>>> +#ifdef CONFIG_DEBUG_FS_MOUNT_RESTRICTED
>>>>>> + if (!allow_debugfs)
>>>>>> + return -EPERM;
>>>>>> +#endif
>>>>> But you are not restricting the ability to mount it here, you are
>>>>> removing the ability for it to even start up at all. What does this
>>>>> break for code that thinks the filesystem is registered (i.e. the call
>>>>> to simple_pin_fs() in start_creating() in fs/debugfs/inode.c?
>>>>>
>>>> If it does, the lines below is also cause the same problem.
>>> In a working system, errors in the lines below will never happen :)
>> I think it is not unreasonable to expect that debug functionality are robust enough to handle
>> system where not everything is working smoothly.
> I do not disagree, but have you tested this to ensure that your kernel
> still works when you disable debugfs in this manner?

So far only tested on fedora f32 (x86_64) and older arm64 systems.

So far only zswap that prints out that "debugfs initialization failed" and it still works fine.


> If so, great! Just trying to point out a potential problem...


Will do new patchset, im waiting a bit longer to see if there some other comments first.


> thanks,
>
> greg k-h

\
 
 \ /
  Last update: 2020-05-28 14:42    [W:0.053 / U:2.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site