After rename file dentry still holds reference to lower dentry from
previous location. This doesn't matter for data access because data comes
from upper dentry. But this stale lower dentry taints dentry at new
location and turns it into non-pure upper. Such file leaves visible
whiteout entry after remove in directory which shouldn't have whiteouts at
all.

Overlayfs already tracks pureness of file location in oe->opaque.  This
patch just uses that for detecting actual path type.

Comment from Vivek Goyal's patch:

Here are the details of the problem. Do following.

$ mkdir upper lower work merged upper/dir/
$ touch lower/test
$ sudo mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=
work merged
$ mv merged/test merged/dir/
$ rm merged/dir/test
$ ls -l merged/dir/
/usr/bin/ls: cannot access merged/dir/test: No such file or directory
total 0
c????????? ? ? ? ?            ? test

Basic problem seems to be that once a file has been unlinked, a whiteout
has been left behind which was not needed and hence it becomes visible.

Whiteout is visible because parent dir is of not type MERGE, hence
od->is_real is set during ovl_dir_open(). And that means ovl_iterate()
passes on iterate handling directly to underlying fs. Underlying fs does
not know/filter whiteouts so it becomes visible to user.

Why did we leave a whiteout to begin with when we should not have.
ovl_do_remove() checks for OVL_TYPE_PURE_UPPER() and does not leave
whiteout if file is pure upper. In this case file is not found to be pure
upper hence whiteout is left.

So why file was not PURE_UPPER in this case? I think because dentry is
still carrying some leftover state which was valid before rename. For
example, od->numlower was set to 1 as it was a lower file. After rename,
this state is not valid anymore as there is no such file in lower.
Signed-off-by: NKonstantin Khlebnikov <koct9i@gmail.com>
Reported-by: NViktor Stanchev <me@viktorstanchev.com>
Suggested-by: NVivek Goyal <vgoyal@redhat.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=109611Acked-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>

ovl_remove_upper() should do d_drop() only after it successfully
removes the dir, otherwise a subsequent getcwd() system call will
fail, breaking userspace programs.

This is to fix: https://bugzilla.kernel.org/show_bug.cgi?id=110491Signed-off-by: NRui Wang <rui.y.wang@intel.com>
Reviewed-by: NKonstantin Khlebnikov <koct9i@gmail.com>
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

OpenWRT folks reported that overlayfs fails to mount if upper fs is full,
because workdir can't be created.  Wordir creation can fail for various
other reasons too.

There's no reason that the mount itself should fail, overlayfs can work
fine without a workdir, as long as the overlay isn't modified.

So mount it read-only and don't allow remounting read-write.

Add a couple of WARN_ON()s for the impossible case of workdir being used
despite being read-only.

Reported-by: Bastian Bittorf <bittorf@bluebottle.com> 
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Cc: <stable@vger.kernel.org> # v3.18+

When removing an opaque directory we can't just call rmdir() to check for
emptiness, because the directory will need to be replaced with a whiteout.
The replacement is done with RENAME_EXCHANGE, which doesn't check
emptiness.

Solution is just to check emptiness by reading the directory.  In the
future we could add a new rename flag to check for emptiness even for
RENAME_EXCHANGE to optimize this case.
Reported-by: NVincent Batts <vbatts@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>
Tested-by: NJordi Pujol Palomer <jordipujolp@gmail.com>
Fixes: 263b4a0f ("ovl: dont replace opaque dir")
Cc: <stable@vger.kernel.org> # v4.0+

Convert the following where appropriate:

 (1) S_ISLNK(dentry->d_inode) to d_is_symlink(dentry).

 (2) S_ISREG(dentry->d_inode) to d_is_reg(dentry).

 (3) S_ISDIR(dentry->d_inode) to d_is_dir(dentry).  This is actually more
     complicated than it appears as some calls should be converted to
     d_can_lookup() instead.  The difference is whether the directory in
     question is a real dir with a ->lookup op or whether it's a fake dir with
     a ->d_automount op.

In some circumstances, we can subsume checks for dentry->d_inode not being
NULL into this, provided we the code isn't in a filesystem that expects
d_inode to be NULL if the dirent really *is* negative (ie. if we're going to
use d_inode() rather than d_backing_inode() to get the inode pointer).

Note that the dentry type field may be set to something other than
DCACHE_MISS_TYPE when d_inode is NULL in the case of unionmount, where the VFS
manages the fall-through from a negative dentry to a lower layer.  In such a
case, the dentry type of the negative union dentry is set to the same as the
type of the lower dentry.

However, if you know d_inode is not NULL at the call site, then you can use
the d_is_xxx() functions even in a filesystem.

There is one further complication: a 0,0 chardev dentry may be labelled
DCACHE_WHITEOUT_TYPE rather than DCACHE_SPECIAL_TYPE.  Strictly, this was
intended for special directory entry types that don't have attached inodes.

The following perl+coccinelle script was used:

use strict;

my @callers;
open($fd, 'git grep -l \'S_IS[A-Z].*->d_inode\' |') ||
    die "Can't grep for S_ISDIR and co. callers";
@callers = <$fd>;
close($fd);
unless (@callers) {
    print "No matches\n";
    exit(0);
}

my @cocci = (
    '@@',
    'expression E;',
    '@@',
    '',
    '- S_ISLNK(E->d_inode->i_mode)',
    '+ d_is_symlink(E)',
    '',
    '@@',
    'expression E;',
    '@@',
    '',
    '- S_ISDIR(E->d_inode->i_mode)',
    '+ d_is_dir(E)',
    '',
    '@@',
    'expression E;',
    '@@',
    '',
    '- S_ISREG(E->d_inode->i_mode)',
    '+ d_is_reg(E)' );

my $coccifile = "tmp.sp.cocci";
open($fd, ">$coccifile") || die $coccifile;
print($fd "$_\n") || die $coccifile foreach (@cocci);
close($fd);

foreach my $file (@callers) {
    chomp $file;
    print "Processing ", $file, "\n";
    system("spatch", "--sp-file", $coccifile, $file, "--in-place", "--no-show-diff") == 0 ||
	die "spatch failed";
}

[AV: overlayfs parts skipped]
Signed-off-by: NDavid Howells <dhowells@redhat.com>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

This patch adds two macros:

OVL_XATTR_PRE_NAME and OVL_XATTR_PRE_LEN

to present ovl_xattr name prefix and its length. Also, a
new macro OVL_XATTR_OPAQUE is introduced to replace old
*ovl_opaque_xattr*.

Fix the length of "trusted.overlay." to *16*.
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

When removing an empty opaque directory, then it makes no sense to replace
it with an exact replica of itself before removal.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

OVL_PATH_PURE_UPPER -> __OVL_PATH_UPPER | __OVL_PATH_PURE
OVL_PATH_UPPER      -> __OVL_PATH_UPPER
OVL_PATH_MERGE      -> __OVL_PATH_UPPER | __OVL_PATH_MERGE
OVL_PATH_LOWER      -> 0

Multiple R/O layers will allow __OVL_PATH_MERGE without __OVL_PATH_UPPER.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

ovl_remove_and_whiteout() needs to check if upper dentry exists or not
after having locked upper parent directory.

Previously we used a "type" value computed before locking the upper parent
directory, which is susceptible to racing with copy-up.

There's a similar check in ovl_check_empty_and_clear().  This one is not
actually racy, since copy-up doesn't change the "emptyness" property of a
directory.  Add a comment to this effect, and check the existence of upper
dentry locally to make the code cleaner.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree.  All modifications
go to the upper, writable layer.

This type of mechanism is most often used for live CDs but there's a
wide variety of other uses.

The implementation differs from other "union filesystem"
implementations in that after a file is opened all operations go
directly to the underlying, lower or upper, filesystems.  This
simplifies the implementation and allows native performance in these
cases.

The dentry tree is duplicated from the underlying filesystems, this
enables fast cached lookups without adding special support into the
VFS.  This uses slightly more memory than union mounts, but dentries
are relatively small.

Currently inodes are duplicated as well, but it is a possible
optimization to share inodes for non-directories.

Opening non directories results in the open forwarded to the
underlying filesystem.  This makes the behavior very similar to union
mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file
descriptors).

Usage:

  mount -t overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay

The following cotributions have been folded into this patch:

Neil Brown <neilb@suse.de>:
 - minimal remount support
 - use correct seek function for directories
 - initialise is_real before use
 - rename ovl_fill_cache to ovl_dir_read

Felix Fietkau <nbd@openwrt.org>:
 - fix a deadlock in ovl_dir_read_merged
 - fix a deadlock in ovl_remove_whiteouts

Erez Zadok <ezk@fsl.cs.sunysb.edu>
 - fix cleanup after WARN_ON

Sedat Dilek <sedat.dilek@googlemail.com>
 - fix up permission to confirm to new API

Robin Dong <hao.bigrat@gmail.com>
 - fix possible leak in ovl_new_inode
 - create new inode in ovl_link

Andy Whitcroft <apw@canonical.com>
 - switch to __inode_permission()
 - copy up i_uid/i_gid from the underlying inode

AV:
 - ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits
 - ovl_clear_empty() - one failure exit forgetting to do unlock_rename(),
   lack of check for udir being the parent of upper, dropping and regaining
   the lock on udir (which would require _another_ check for parent being
   right).
 - bogus d_drop() in copyup and rename [fix from your mail]
 - copyup/remove and copyup/rename races [fix from your mail]
 - ovl_dir_fsync() leaving ERR_PTR() in ->realfile
 - ovl_entry_free() is pointless - it's just a kfree_rcu()
 - fold ovl_do_lookup() into ovl_lookup()
 - manually assigning ->d_op is wrong.  Just use ->s_d_op.
 [patches picked from Miklos]:
 * copyup/remove and copyup/rename races
 * bogus d_drop() in copyup and rename

Also thanks to the following people for testing and reporting bugs:

  Jordi Pujol <jordipujolp@gmail.com>
  Andy Whitcroft <apw@canonical.com>
  Michal Suchanek <hramrach@centrum.cz>
  Felix Fietkau <nbd@openwrt.org>
  Erez Zadok <ezk@fsl.cs.sunysb.edu>
  Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>