mysterious sysctl failure on nullfs mount

[Kostik Belousov]

On Sat, Dec 10, 2011 at 10:50:07AM -0500, Kamil Choudhury wrote:
> Hi all:
> 
> I've been trying to figure out what's going on with this bug for a few days now:
> 
> http://docs.freebsd.org/cgi/getmsg.cgi?fetch=899628+0+current/freebsd-ports-bugs
> 
> Summary: you mount the virtualbox binaries to /usr/local/ via nullfs, and
> execution fails with a syctl error.
> 
> I've figured out the bit of code that's causing the error, and I've
> encapsulated it in the following (small) program:
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <errno.h>
> #include <sys/param.h>
> #include <sys/sysctl.h>
> 
> int main( void )
> {
>         char g_szSupLibHardenedExePath[5000];
>         int aiName[4];
>         aiName[0] = CTL_KERN;
>         aiName[1] = KERN_PROC;
>         aiName[2] = KERN_PROC_PATHNAME;
>         aiName[3] = getpid();
> 
>         size_t cbPath = sizeof( g_szSupLibHardenedExePath );
>         printf( "%d\n", cbPath );
>         if(sysctl(aiName, 4, g_szSupLibHardenedExePath, &cbPath, NULL, 0) < 0)
>                 printf( "sysctl failed" );
>         else
>                 printf( "sysctl succeeded" );
> 
>         return( 0 );
> }
> 
> Here's where it gets weird: if the code is executed in in
> /usr/local/lib/virtualbox, it fails with the sysctl error. If the code is
> executed in another location on the *same* nullfs mount (say,
> /usr/local/bin/), it executes fine.
> 
> There seems to be a something at a filesystem level that's preventing
> execution -- does anyone on the list know what that something may be?
You did not specified which version of the OS you are running.
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