linux-kernel - Re: 2.6.25 Kernel - Problems with capabilities

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Date:	Mon, 21 Apr 2008 21:28:11 +0100
From:	David <david@...olicited.net>
To:	serge@...lyn.com
CC:	casey@...aufler-ca.com, Mike Galbraith <efault@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morgan <morgan@...nel.org>
Subject: Re: 2.6.25 Kernel - Problems with capabilities

serge@...lyn.com wrote:
> Quoting David (david@...olicited.net):
>   
>> serge@...lyn.com wrote:
>>     
>>>> /lib/libcap.so.1 -> libcap.so.1.92
>>>>
>>>> I guess that's 1.92 (should be the version shipped with SuSE 9.1).
>>>>     
>>>>         
>>> Ok, thanks, then it's definately not what I was thinking.
>>>
>>> (Will wait to check out your strace)
>>>   
>>>       
>> strace attached.
>>
>> Cheers
>> David
>>
>>     
>
> ...
>   
>> capget(0x20071026, 0, {, , })           = -1 EINVAL (Invalid argument)
>>     
>
> This is odd.  libcap-1.x should be passing in 0x19980330.
>
> Next, given the -EINVAL return value ntpd should be seeing a NULL result
> from cap_get_proc() and exiting right there.
>
> What version of ntpd is this?  (I must be looking at a wrong value, but
> even so the fact that cap_get_proc()->capget() is using 0x20071026 for
> version doesn't make sense)
>
>   
>> capset(0, 0, {CAP_NET_BIND_SERVICE|CAP_SYS_TIME, CAP_NET_BIND_SERVICE|CAP_SYS_TIME, CAP_NET_BIND_SERVICE|CAP_SYS_TIME}) = -1 EINVAL (Invalid argument)
>> time(NULL)                              = 1208803493
>> write(5, "21 Apr 19:44:53 ntpd[6118]: cap_"..., 92) = 92
>> munmap(0x40022000, 4096)                = 0
>> exit_group(-1)                          = ?
>> Process 6118 detached
>>     
>
>   
Oh dear .. more investigation... here's the source from libcap-1.92. 
capget() is being called with null arguments, which I guess returns with 
the latest version in ch.version ?

The switch then fails and the set gets called with version = 0 ??

Cheers
David

void _libcap_establish_api(void)
{
    struct __user_cap_header_struct ch;
    struct __user_cap_data_struct cs;

    if (_libcap_kernel_version) {
        _cap_debug("already identified kernal api 0x%.8x",
                   _libcap_kernel_version);
        return;
    }

    memset(&ch, 0, sizeof(ch));
    memset(&cs, 0, sizeof(cs));

    (void) capget(&ch, &cs);

    switch (ch.version) {

    case 0x19980330:
        _libcap_kernel_version = 0x19980330;
        _libcap_kernel_features = CAP_FEATURE_PROC;
        break;

    case 0x19990414:
        _libcap_kernel_version = 0x19990414;
        _libcap_kernel_features = CAP_FEATURE_PROC|CAP_FEATURE_FILE;
        break;

    default:
        _libcap_kernel_version = 0x00000000;
        _libcap_kernel_features = 0x00000000;
    }

    _cap_debug("version: %x, features: %x\n",
               _libcap_kernel_version, _libcap_kernel_features);
}


> thanks,
> -serge
>   

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