capable()-function

capable()-function

[Tony Glader]

Hi!

I was investigating problems with PCMCIA and found that
capable(CAP_SYS_ADMIN) returns always false in my case. If I'm calling
capable(CAP_SYS_ADMIN) as root - shouldn't it return true? What could
cause this? I'm using RH 8.0 and src-rpm of 2.4.18-14 kernel.

-- 
* Tony Glader 

Re: capable()-function

[Chris Wright]

* Tony Glader (Tony.Glader@blueberrysolutions.com) wrote:
> Hi!
> 
> I was investigating problems with PCMCIA and found that
> capable(CAP_SYS_ADMIN) returns always false in my case. If I'm calling
> capable(CAP_SYS_ADMIN) as root - shouldn't it return true? What could
> cause this? I'm using RH 8.0 and src-rpm of 2.4.18-14 kernel.

Well, it will return true if you _have_ CAP_SYS_ADMIN capability.
Typically root has all effective capabilities (except CAP_SETPCAP).
You can check your effective capabilities in /proc/[pid]/status.
I doubt your system can't get a process with CAP_SYS_ADMIN, you'd have
trouble mounting filesystems, etc... 

thanks,
-chris
-- 
Linux Security Modules     http://lsm.immunix.org     http://lsm.bkbits.net

Re: capable()-function

[Tony Glader]

On Wed, 9 Oct 2002, Chris Wright wrote:

> > I was investigating problems with PCMCIA and found that
> > capable(CAP_SYS_ADMIN) returns always false in my case. If I'm calling
> Typically root has all effective capabilities (except CAP_SETPCAP).
> You can check your effective capabilities in /proc/[pid]/status.

In this case capable() call has been made from a kernel module. I think a
module doesn't have a PID? Should I check capabilites of program that does
a ioctl() call that will cause module to do capable() checking?

Process that does ioctl() call is owned by root and has following 
capabilities:

CapInh: 0000000000000000
CapPrm: 00000000fffffeff
CapEff: 00000000fffffeff
 
I think there are at least CAP_SYS_ADMIN capability.

-- 
* Tony Glader 

Re: capable()-function

[Chris Wright]

* Tony Glader (Tony.Glader@blueberrysolutions.com) wrote:
> On Wed, 9 Oct 2002, Chris Wright wrote:
> 
> > > I was investigating problems with PCMCIA and found that
> > > capable(CAP_SYS_ADMIN) returns always false in my case. If I'm calling
> > Typically root has all effective capabilities (except CAP_SETPCAP).
> > You can check your effective capabilities in /proc/[pid]/status.
> 
> In this case capable() call has been made from a kernel module. I think a
> module doesn't have a PID? Should I check capabilites of program that does
> a ioctl() call that will cause module to do capable() checking?

The userspace task that called the ioctl() is the one to look at.

> Process that does ioctl() call is owned by root and has following 
> capabilities:
> 
> CapInh: 0000000000000000
> CapPrm: 00000000fffffeff
> CapEff: 00000000fffffeff

Ok, I don't think the capable() check is failing.
-chris
-- 
Linux Security Modules     http://lsm.immunix.org     http://lsm.bkbits.net

Re: capable()-function

[Tony Glader]

On Wed, 9 Oct 2002, Chris Wright wrote:

> > In this case capable() call has been made from a kernel module. I think a
> The userspace task that called the ioctl() is the one to look at.

...

> > CapInh: 0000000000000000
> > CapPrm: 00000000fffffeff
> > CapEff: 00000000fffffeff
> 
> Ok, I don't think the capable() check is failing.

So though me too, but now we are getting to the point - capable() check 
fails! How that can be possible?

-- 
* Tony Glader 

Re: capable()-function

[Chris Wright]

* Tony Glader (Tony.Glader@blueberrysolutions.com) wrote:
> On Wed, 9 Oct 2002, Chris Wright wrote:
> 
> > > In this case capable() call has been made from a kernel module. I think a
> > The userspace task that called the ioctl() is the one to look at.
> 
> ...
> 
> > > CapInh: 0000000000000000
> > > CapPrm: 00000000fffffeff
> > > CapEff: 00000000fffffeff
> > 
> > Ok, I don't think the capable() check is failing.
> 
> So though me too, but now we are getting to the point - capable() check 
> fails! How that can be possible?

You could dump something like this before the capable() call:

printk(KERN_DEBUG "%s:(%d) eff: 0x%x\n", current->comm, current->pid,
						cap_t(current->cap_effective));
-chris
-- 
Linux Security Modules     http://lsm.immunix.org     http://lsm.bkbits.net

Re: capable()-function

[Tony Glader]

On Wed, 9 Oct 2002, Chris Wright wrote:

> You could dump something like this before the capable() call:
> 
> printk(KERN_DEBUG "%s:(%d) eff: 0x%x\n", current->comm, current->pid,
> 						cap_t(current->cap_effective));

Ok. I got following result:

ÿÿ:(12290) eff: 0x0

Is the eff-value current capabilities? Why it is zero? The task who called 
it (cardmgr) was owned by root.

-- 
* Tony Glader