mount --bind and -o [re: nosuid/noexec/nodev handling]

[Ville Herva <vherva@mail.niksula.cs.hut.fi>]

On 2001-09-12 17:30:22 you wrote:
>
> nosuid, noexec and nodev are made vfsmount flags (instead of
> superblock ones).  Places that used to check them switched to checking
> vfsmount->mnt_flags.  get_filesystem_info() updated, ditto for
> do_add_mount() and do_remount(). 
>
> As the result, these flags are per-mountpoint now.  E.g. we can turn them
> on and off for arbitrary subtree:
> 
> mount --bind /home/luser /home/luser
> mount -o remount,noexec /home/luser
> 
> will turn noexec on for subtree at /hom/luser without affecting the rest
> /of home.  Other obvious applications is mounting a filesystem nosuid for
> chroot jail and normally outside of it, yodda, yodda.
> 
> Patch is completely straightforward.  Works here and it had been in ac for
> -a month (i.e. since 2.4.8-ac2).  Please, apply.

Ummh, is there a reason for this behaviour?

$ mount --bind -o noexec /bin /home/sftp/bin
$ mount 
(...)
/bin on /home/sftp/bin type none (rw,noexec,bind)
$ cd /home/sftp/bin
$ ./uname -a
Linux babbage 2.4.10-ac10 #4 SMP Wed Oct 10 11:39:11 EEST 2001 i686 unknown
$ mount -o remount,noexec /home/sftp/bin
$ mount 
(...)
/bin on /home/sftp/bin type none (rw,noexec,bind)
$ ./uname -a
zsh: permission denied: ./uname

That seems like a bug to me. At very least, mount shouldn't report noexec if
the mount point isn't. Or am I missing something?

Further:

$ mount --bind -o ro /bin /home/sftp/bin 
$ mount -o remount,ro,nosuid /home/sftp/bin 
$ mount: /home/sftp/bin is busy      
$ mount
(...)
/bin on /home/sftp/bin type none (ro,bind)
$ cd /home/sftp/bin
$ touch asdakhsdhdh
$ ls asdakhsdhdh
asdakhsdhdh

So I suppose ro (umask, some others as well) is not supported for --bind
mounted mount points? Would it be possible to have mount to report error if
non-functional -o options are passed to it?

And btw, thanks. --bind is a damn cool feature to have.


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