Re: pivot_root seems to be broken in 2.4.21-ac4

["Mika Penttilä" <mika.penttila@kolumbus.fi>]

Alan Cox wrote:

>On Maw, 2003-07-22 at 18:37, Jason Baron wrote:
>  
>
>>>I tell init to re-execute itself (after pivot_root and thus from the new 
>>>root fs), which causes init to close its old fds and open new ones from 
>>>the new root fs with. This is necessary because init already runs as pid 
>>>1 when I start the root fs switching. Maybe something changed with the 
>>>kernel process fds from 2.4.21-rc2 to 2.4.21-ac4 ?
>>>
>>>      
>>>
>>yes, see the addition of the unshare_files function in kernel/fork.c
>>    
>>
>
>Shouldnt really have changed anything except for security exploits and
>threaded apps doing weird stuff. In normal situations the files count is
>one so we should actually be executing nothing more exciting that an
>atomic_inc/atomic_dec.
>
>I wonder what is going on here.
>
>-
>  
>
But kernel threads may be incrementing init's files->count before user 
space init execs, so unshare_files() after execve("/sbin/init") ends up 
copying files.

--Mika