• Miklos Szeredi's avatar
    [PATCH] namespace.c: fix bind mount from foreign namespace · 68b47139
    Miklos Szeredi authored
    I'm resending this patch, because I still believe it's the correct fix.
    
    Tested before/after applying the patch with a test application
    available from:
    
      http://www.inf.bme.hu/~mszeredi/nstest.c
    
    Bind mount from a foreign namespace results in an un-removable mount.
    The reason is that mnt->mnt_namespace is copied from the old mount in
    clone_mnt().  Because of this check_mnt() in sys_umount() will fail.
    
    The solution is to set mnt->mnt_namespace to current->namespace in
    clone_mnt().  clone_mnt() is either called from do_loopback() or
    copy_tree().  copy_tree() is called from do_loopback() or
    copy_namespace().
    
    When called (directly or indirectly) from do_loopback(), always
    current->namspace is being modified: check_mnt(nd->mnt).  So setting
    mnt->mnt_namespace to current->namspace is the right thing to do.
    
    When called from copy_namespace(), the setting of mnt_namespace is
    irrelevant, since mnt_namespace is reset later in that function for
    all copied mounts.
    
    Jamie said:
    
      This patch is correct.  The old code was buggy for more fundamental and
      serious reason: it broke the invariant that a tree of vfsmnts all have the
      same value of mnt_namespace (and the same for the mnt_list list).
    Signed-off-by: default avatarMiklos Szeredi <miklos@szeredi.hu>
    Acked-by: default avatarJamie Lokier <jamie@shareable.org>
    Cc: <viro@parcelfarce.linux.theplanet.co.uk>
    Cc: Christoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    68b47139
namespace.c 34.9 KB