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comp.lang.ruby

execve syscall in ruby

Daniel Kami??ski

7/19/2008 6:43:00 PM

Hi
I've tried to call execve using Kernel#syscall. Execve is 11 in my case
[i386] so i'm trying to call:

syscall(11, '/bin/true', ['true'].pack('p*') , ['X=1'].pack('p*'))

but it raises Bad address (Errno::EFAULT) exception, called it with
strace:

% strace -eexecve ruby -e "syscall(11, '/bin/true', ['true'].pack('p*')
, ['X=1'].pack('p*'))"
execve("/usr/bin/ruby", ["ruby", "-e", "syscall(11, \'/bin/true\',
[\'true\'"...], [/* 75 vars */]) = 0
execve("/bin/true", ["true"..., 0x4800, 0x6000000, 0x11, "\7!"...,
""..., 0x7000000, 0x49, "\7!"...,
"\310\261\371A\310\261\371A\320\261\371A\320\261\371A\330\261\371A\330\261\371A\340\261\371A\340\261\371A"...],
[/* 4 vars */]) = -1 EFAULT (Bad address)
-e:1:in `syscall': Bad address (Errno::EFAULT)
from -e:1

execve(2) man says:
EFAULT filename points outside your accessible address space.

Both execve traces differs, second argument [an arguments array] in
second execve doesn't look the same like in first execve invocation,
it's longer, has addidional values and ... [three dots] after strings
suggesting they're in fact probably longer [i don't know strace
formatting rules well]. Is it something wrong with p* packing? Anybody
tried calling execve in ruby this way?:)
--
Posted via http://www.ruby-....
6 Answers

Daniel Kami??ski

7/19/2008 7:37:00 PM

0

That's me again, now i know that i have to terminate an array with null
pointer, is this possible in ruby?


--
Posted via http://www.ruby-....

Rolando Abarca

7/19/2008 8:49:00 PM

0

On 19-07-2008, at 15:36, Daniel Kaminski wrote:

> That's me again, now i know that i have to terminate an array with
> null
> pointer, is this possible in ruby?

NULL is just a 0 (zero):

$ ruby -e "syscall(11, '/home/rolando/test.rb', ['true', 'lala',
0].pack('ppi'), ['X=1', 0].pack('pi'))"
["lala"]
{"X"=>"1"}

$ cat test.rb
#!/usr/local/bin/ruby

p ARGV
p ENV

> --
> Posted via http://www.ruby-....


regards,
--
Rolando Abarca M.

Daniel Kami??ski

7/19/2008 9:01:00 PM

0

Rolando Abarca wrote:
> On 19-07-2008, at 15:36, Daniel Kaminski wrote:
>
>> That's me again, now i know that i have to terminate an array with
>> null
>> pointer, is this possible in ruby?
>
> NULL is just a 0 (zero):
>
> $ ruby -e "syscall(11, '/home/rolando/test.rb', ['true', 'lala',
> 0].pack('ppi'), ['X=1', 0].pack('pi'))"
> ["lala"]
> {"X"=>"1"}
>
> $ cat test.rb
> #!/usr/local/bin/ruby
>
> p ARGV
> p ENV


-e:1:in `syscall': string contains null byte (ArgumentError)
from -e:1

It's the same error when tried ['true', nil].pack('p*'), result is the
same too, it adds '000\000\000\000'.
Do you have patched ruby build or something? i managed to make it work
by commenting few lines from string.c responsible for above exception.

regards:-)

--
Posted via http://www.ruby-....

Daniel Kami??ski

7/19/2008 9:14:00 PM

0

Ah, stupid me, haven't noticed a bug:
http://rubyforge.org/tracker/index.php?func=detail&aid=20895&group_id=426&...
--
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Rolando Abarca

7/19/2008 9:55:00 PM

0

On 19-07-2008, at 17:01, Daniel Kaminski wrote:

> Rolando Abarca wrote:
>> On 19-07-2008, at 15:36, Daniel Kaminski wrote:
>>
>>> That's me again, now i know that i have to terminate an array with
>>> null
>>> pointer, is this possible in ruby?
>>
>> NULL is just a 0 (zero):
>>
>> $ ruby -e "syscall(11, '/home/rolando/test.rb', ['true', 'lala',
>> 0].pack('ppi'), ['X=1', 0].pack('pi'))"
>> ["lala"]
>> {"X"=>"1"}
>>
>> $ cat test.rb
>> #!/usr/local/bin/ruby
>>
>> p ARGV
>> p ENV
>
>
> -e:1:in `syscall': string contains null byte (ArgumentError)
> from -e:1
>
> It's the same error when tried ['true', nil].pack('p*'), result is the
> same too, it adds '000\000\000\000'.
> Do you have patched ruby build or something? i managed to make it work
> by commenting few lines from string.c responsible for above exception.
>
> regards:-)

I think you're missing the fact that I used 'ppi' as the argument to
pack (NULL is an integer) and not 'p*'.
regards,
--
Rolando Abarca M.

Daniel Kami??ski

7/19/2008 10:50:00 PM

0

Rolando Abarca wrote:
>
> I think you're missing the fact that I used 'ppi' as the argument to
> pack (NULL is an integer) and not 'p*'.
> regards,

Except that the problem is already solved [see above, pasted a link] you
seems to be missing the fact that I was saing that ['true',0
].pack('pi') and ['true',nil ].pack('p*') gives the same result and the
p* method is better because you don't have to control 'p' count in
pack() argument.

--
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