• Andreas Gruenbacher's avatar
    [PATCH] Fix d_path for lazy unmounts · eb3dfb0c
    Andreas Gruenbacher authored
    Here is a bugfix to d_path.
    First, when d_path() hits a lazily unmounted mount point, it tries to
    prepend the name of the lazily unmounted dentry to the path name.  It gets
    this wrong, and also overwrites the slash that separates the name from the
    following pathname component.  This is demonstrated by the attached test
    case, which prints "getcwd returned d_path-bugsubdir" with the bug.  The
    correct result would be "getcwd returned d_path-bug/subdir".
    It could be argued that the name of the root dentry should not be part of
    the result of d_path in the first place.  On the other hand, what the
    unconnected namespace was once reachable as may provide some useful hints
    to users, and so that seems okay.
    Second, it isn't always possible to tell from the __d_path result whether
    the specified root and rootmnt (i.e., the chroot) was reached: lazy
    unmounts of bind mounts will produce a path that does start with a
    non-slash so we can tell from that, but other lazy unmounts will produce a
    path that starts with a slash, just like "ordinary" paths.
    The attached patch cleans up __d_path() to fix the bug with overlapping
    pathname components.  It also adds a @fail_deleted argument, which allows
    to get rid of some of the mess in sys_getcwd().  Grabbing the dcache_lock
    can then also be moved into __d_path().  The patch also makes sure that
    paths will only start with a slash for paths which are connected to the
    root and rootmnt.
    The @fail_deleted argument could be added to d_path() as well: this would
    allow callers to recognize deleted files, without having to resort to the
    ambiguous check for the " (deleted)" string at the end of the pathnames.
    This is not currently done, but it might be worthwhile.
    Signed-off-by: default avatarAndreas Gruenbacher <agruen@suse.de>
    Cc: Neil Brown <neilb@suse.de>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: Christoph Hellwig <hch@lst.de>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
dcache.c 54.3 KB