On Feb 14, 2011, at 11:41 AM, Cyril Hrubis wrote:
> Hi!
>>>> Hmm I see the problem now. However as a root, I could read and run files
>>>> with just an exec flag, at least here. I suppose the test works here by
>>>> some saved-id magick. I'll look deeper into this.
>>>>
>>>
>>> I think I've found the cause. The wait() funcion returns -1 if exec*
>>> hasn't succeded to run the file (and sets the status to 0). I'm not sure
>>> if this is POSIX compilant behaviour, I'll check on that later.
>>>
>>> What flavour of glibc/kernel are you testing there, it seems that it
>>> behaves a little different than mine. Here I have glibc-2.11.
>>>
>>> Anyway, I'll fix the test to check for return value from wait(), add the
>>> fix for octal file mode and fix the runtest files.
>>
>> Grr, got myself caught. Strace behaves differently when running with
>> root + setegid + exec, so lets start digging again.
>>
>
> Okay, seems that linux kernel (at least here) allows you to execute
> file if your user/group/other has at least execute rights and real uid 0.
>
> That is the reason why these tests runs fine here.
Maybe Linux has now adopted the philosophy that has broken BSD for some
time with [e]access(2), where it will always succeed for root regardless of
whether or not root really has the ability to read the file per the file mode,
e.g.?
%test -w usb.img
%echo $?
1
%exit
# sudo test -w usb.img
# echo $?
0
# exit
$ test -w usb.img
$ echo $?
0
$ ls -l usb.img
-rw-r--r-- 1 garrcoop garrcoop 188743680 Oct 21 15:49 usb.img
Assume $ is me, % is someone else, and # is sudo'ed to root.
Cheers,
-Garrett
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