nullfs distinct path check: take into account filesystems

[Gleb Kurtsou]

On (31/05/2010 19:54), Andriy Gapon wrote:
> 
> Right now mount_nullfs doesn't allow to, for example, mount / in /tmp/somedir even
> if /tmp is a different filesystem.
> I think there is no reason to do that and thus propose the following patch.
Why don't we remove mount_nullfs entirely? Such check is trivial to do
in kernel, all is needed is to change mntopts and add compatibility
shims.

Take a look at pefs_mount if interested:
http://github.com/glk/pefs/blob/master/sys/fs/pefs/pefs_vfsops.c

There is no mount_pefs and 'pefs mount' command exec's /sbin/mount,
'mount -t pefs' is supported as well; search for pefs_mount in:
http://github.com/glk/pefs/blob/master/sbin/pefs/pefs_ctl.c

Thanks,
Gleb.

> 
> diff --git a/sbin/mount_nullfs/mount_nullfs.c b/sbin/mount_nullfs/mount_nullfs.c
> index abca9fa..4bd426f 100644
> --- a/sbin/mount_nullfs/mount_nullfs.c
> +++ b/sbin/mount_nullfs/mount_nullfs.c
> @@ -46,6 +46,7 @@ static const char rcsid[] =
> 
>  #include <sys/param.h>
>  #include <sys/mount.h>
> +#include <sys/stat.h>
>  #include <sys/uio.h>
> 
>  #include <err.h>
> @@ -62,7 +63,8 @@ struct mntopt mopts[] = {
>  	MOPT_END
>  };
> 
> -int	subdir(const char *, const char *);
> +static int	samefs(const char *p1, const char *p2);
> +static int	subdir(const char *, const char *);
>  static void	usage(void) __dead2;
> 
>  int
> @@ -93,7 +95,8 @@ main(int argc, char *argv[])
>  	(void)checkpath(argv[0], target);
>  	(void)checkpath(argv[1], source);
> 
> -	if (subdir(target, source) || subdir(source, target))
> +	if (samefs(target, source)
> +	    && (subdir(target, source) || subdir(source, target)))
>  		errx(EX_USAGE, "%s (%s) and %s are not distinct paths",
>  		    argv[0], target, argv[1]);
> 
> @@ -116,6 +119,21 @@ main(int argc, char *argv[])
>  }
> 
>  int
> +samefs(const char *p1, const char *p2)
> +{
> +	struct stat sb;
> +	uint32_t fsid1;
> +	uint32_t fsid2;
> +
> +	stat(p1, &sb);
> +	fsid1 = sb.st_dev;
> +	stat(p2, &sb);
> +	fsid2 = sb.st_dev;
> +
> +	return (fsid1 == fsid2);
> +}
> +
> +int
>  subdir(const char *p, const char *dir)
>  {
>  	int l;
> 
> -- 
> Andriy Gapon
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