Remove duplicated include.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

Setting POSIX ACL needs special handling:

1) Some permission checks are done by ->setxattr() which now uses mounter's
creds ("ovl: do operations on underlying file system in mounter's
context").  These permission checks need to be done with current cred as
well.

2) Setting ACL can fail for various reasons.  We do not need to copy up in
these cases.

In the mean time switch to using generic_setxattr.

[Arnd Bergmann] Fix link error without POSIX ACL. posix_acl_from_xattr()
doesn't have a 'static inline' implementation when CONFIG_FS_POSIX_ACL is
disabled, and I could not come up with an obvious way to do it.

This instead avoids the link error by defining two sets of ACL operations
and letting the compiler drop one of the two at compile time depending
on CONFIG_FS_POSIX_ACL. This avoids all references to the ACL code,
also leading to smaller code.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

Inode attributes are copied up to overlay inode (uid, gid, mode, atime,
mtime, ctime) so generic code using these fields works correcty.  If a hard
link is created in overlayfs separate inodes are allocated for each link.
If chmod/chown/etc. is performed on one of the links then the inode
belonging to the other ones won't be updated.

This patch attempts to fix this by sharing inodes for hard links.

Use inode hash (with real inode pointer as a key) to make sure overlay
inodes are shared for hard links on upper.  Hard links on lower are still
split (which is not user observable until the copy-up happens, see
Documentation/filesystems/overlayfs.txt under "Non-standard behavior").

The inode is only inserted in the hash if it is non-directoy and upper.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

To get from overlay inode to real inode we currently use 'struct
ovl_entry', which has lifetime connected to overlay dentry.  This is okay,
since each overlay dentry had a new overlay inode allocated.

Following patch will break that assumption, so need to leave out ovl_entry.
This patch stores the real inode directly in i_private, with the lowest bit
used to indicate whether the inode is upper or lower.

Lifetime rules remain, using ovl_inode_real() must only be done while
caller holds ref on overlay dentry (and hence on real dentry), or within
RCU protected regions.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

Fix atime update logic in overlayfs.

This patch adds an i_op->update_time() handler to overlayfs inodes.  This
forwards atime updates to the upper layer only.  No atime updates are done
on lower layers.

Remove implicit atime updates to underlying files and directories with
O_NOATIME.  Remove explicit atime update in ovl_readlink().

Clear atime related mnt flags from cloned upper mount.  This means atime
updates are controlled purely by overlayfs mount options.

Reported-by: Konstantin Khlebnikov <koct9i@gmail.com> 
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

The fact that we always do permission checking on the overlay inode and
clear MAY_WRITE for checking access to the lower inode allows cruft to be
removed from ovl_permission().

1) "default_permissions" option effectively did generic_permission() on the
overlay inode with i_mode, i_uid and i_gid updated from underlying
filesystem.  This is what we do by default now.  It did the update using
vfs_getattr() but that's only needed if the underlying filesystem can
change (which is not allowed).  We may later introduce a "paranoia_mode"
that verifies that mode/uid/gid are not changed.

2) splitting out the IS_RDONLY() check from inode_permission() also becomes
unnecessary once we remove the MAY_WRITE from the lower inode check.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

Now we are planning to do DAC permission checks on overlay inode
itself. And to make it work, we will need to make sure we can get acls from
underlying inode. So define ->get_acl() for overlay inodes and this in turn
calls into underlying filesystem to get acls, if any.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

No point in keeping overlay inodes around since they will never be reused.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

The hash salting changes meant that we can no longer reuse the hash in the
overlay dentry to look up the underlying dentry.

Instead of lookup_hash(), use lookup_one_len_unlocked() and swith to
mounter's creds (like we do for all other operations later in the series).

Now the lookup_hash() export introduced in 4.6 by 3c9fe8cd ("vfs: add
lookup_hash() helper") is unused and can possibly be removed; its
usefulness negated by the hash salting and the idea that mounter's creds
should be used on operations on underlying filesystems.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Fixes: 8387ff25 ("vfs: make the string hashes salt the hash")

overlay needs underlying fs to support d_type. Recently I put in a
patch in to detect this condition and started failing mount if
underlying fs did not support d_type.

But this breaks existing configurations over kernel upgrade. Those who
are running docker (partially broken configuration) with xfs not
supporting d_type, are surprised that after kernel upgrade docker does
not run anymore.

https://github.com/docker/docker/issues/22937#issuecomment-229881315

So instead of erroring out, detect broken configuration and warn
about it. This should allow existing docker setups to continue
working after kernel upgrade.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Fixes: 45aebeaf ("ovl: Ensure upper filesystem supports d_type")
Cc: <stable@vger.kernel.org> 4.6

The two methods essentially do the same: find the real dentry/inode
belonging to an overlay dentry.  The difference is in the usage:

vfs_open() uses ->d_select_inode() and expects the function to perform
copy-up if necessary based on the open flags argument.

file_dentry() uses ->d_real() passing in the overlay dentry as well as the
underlying inode.

vfs_rename() uses ->d_select_inode() but passes zero flags.  ->d_real()
with a zero inode would have worked just as well here.

This patch merges the functionality of ->d_select_inode() into ->d_real()
by adding an 'open_flags' argument to the latter.

[Al Viro] Make the signature of d_real() match that of ->d_real() again.
And constify the inode argument, while we are at it.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

d_type check requires successful creation of workdir as iterates
through work dir and expects work dir to be present in it. If that's
not the case, this check will always return d_type not supported even
if underlying filesystem might be supporting it.

So don't do this check if work dir creation failed in previous step.
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

In user namespace the whiteout creation fails with -EPERM because the
current process isn't capable(CAP_SYS_ADMIN) when setting xattr.

A simple reproducer:

$ mkdir upper lower work merged lower/dir
$ sudo mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merged
$ unshare -m -p -f -U -r bash

Now as root in the user namespace:

\# touch merged/dir/{1,2,3} # this will force a copy up of lower/dir
\# rm -fR merged/*

This ends up failing with -EPERM after the files in dir has been
correctly deleted:

unlinkat(4, "2", 0)                     = 0
unlinkat(4, "1", 0)                     = 0
unlinkat(4, "3", 0)                     = 0
close(4)                                = 0
unlinkat(AT_FDCWD, "merged/dir", AT_REMOVEDIR) = -1 EPERM (Operation not
permitted)

Interestingly, if you don't place files in merged/dir you can remove it,
meaning if upper/dir does not exist, creating the char device file works
properly in that same location.

This patch uses ovl_sb_creator_cred() to get the cred struct from the
superblock mounter and override the old cred with these new ones so that
the whiteout creation is possible because overlay is wrong in assuming that
the creds it will get with prepare_creds will be in the initial user
namespace.  The old cap_raise game is removed in favor of just overriding
the old cred struct.

This patch also drops from ovl_copy_up_one() the following two lines:

override_cred->fsuid = stat->uid;
override_cred->fsgid = stat->gid;

This is because the correct uid and gid are taken directly with the stat
struct and correctly set with ovl_set_attr().
Signed-off-by: NAntonio Murdaca <runcom@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

Generally permission checking is not necessary when overlayfs looks up a
dentry on one of the underlying layers, since search permission on base
directory was already checked in ovl_permission().

More specifically using lookup_one_len() causes a problem when the lower
directory lacks search permission for a specific user while the upper
directory does have search permission.  Since lookups are cached, this
causes inconsistency in behavior: success depends on who did the first
lookup.

So instead use lookup_hash() which doesn't do the permission check.
Reported-by: NIgnacy Gawędzki <ignacy.gawedzki@green-communications.fr>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

This series fixes bugs in nfs and ext4 due to 4bacc9c9 ("overlayfs:
Make f_path always point to the overlay and f_inode to the underlay").

Regular files opened on overlayfs will result in the file being opened on
the underlying filesystem, while f_path points to the overlayfs
mount/dentry.

This confuses filesystems which get the dentry from struct file and assume
it's theirs.

Add a new helper, file_dentry() [*], to get the filesystem's own dentry
from the file.  This checks file->f_path.dentry->d_flags against
DCACHE_OP_REAL, and returns file->f_path.dentry if DCACHE_OP_REAL is not
set (this is the common, non-overlayfs case).

In the uncommon case it will call into overlayfs's ->d_real() to get the
underlying dentry, matching file_inode(file).

The reason we need to check against the inode is that if the file is copied
up while being open, d_real() would return the upper dentry, while the open
file comes from the lower dentry.

[*] If possible, it's better simply to use file_inode() instead.
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Tested-by: NGoldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: NTrond Myklebust <trond.myklebust@primarydata.com>
Cc: <stable@vger.kernel.org> # v4.2
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Daniel Axtens <dja@axtens.net>

In some instances xfs has been created with ftype=0 and there if a file
on lower fs is removed, overlay leaves a whiteout in upper fs but that
whiteout does not get filtered out and is visible to overlayfs users.

And reason it does not get filtered out because upper filesystem does
not report file type of whiteout as DT_CHR during iterate_dir().

So it seems to be a requirement that upper filesystem support d_type for
overlayfs to work properly. Do this check during mount and fail if d_type
is not supported.
Suggested-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NVivek Goyal <vgoyal@redhat.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

This patch hides error about missing lowerdir if MS_SILENT is set.

We use mount(NULL, "/", "overlay", MS_SILENT, NULL) for testing support of
overlayfs: syscall returns -ENODEV if it's not supported. Otherwise kernel
automatically loads module and returns -EINVAL because lowerdir is missing.
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>

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>

This adds missing .d_select_inode into alternative dentry_operations.
Signed-off-by: NKonstantin Khlebnikov <koct9i@gmail.com>
Fixes: 7c03b5d4 ("ovl: allow distributed fs as lower layer")
Fixes: 4bacc9c9 ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Reviewed-by: NNikolay Borisov <kernel@kyup.com>
Tested-by: NNikolay Borisov <kernel@kyup.com>
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org> # 4.2+

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>

i386 allmodconfig:

  In file included from fs/overlayfs/super.c:10:0:
  fs/overlayfs/super.c: In function 'ovl_fill_super':
  include/linux/fs.h:898:36: error: 'PAGE_CACHE_SIZE' undeclared (first use in this function)
   #define MAX_LFS_FILESIZE (((loff_t)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)
                                      ^
  fs/overlayfs/super.c:939:19: note: in expansion of macro 'MAX_LFS_FILESIZE'
    sb->s_maxbytes = MAX_LFS_FILESIZE;
                     ^
  include/linux/fs.h:898:36: note: each undeclared identifier is reported only once for each function it appears in
   #define MAX_LFS_FILESIZE (((loff_t)PAGE_CACHE_SIZE << (BITS_PER_LONG-1))-1)
                                      ^
  fs/overlayfs/super.c:939:19: note: in expansion of macro 'MAX_LFS_FILESIZE'
    sb->s_maxbytes = MAX_LFS_FILESIZE;
                     ^

Cc: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Without this copy-up of a file can be forced, even without actually being
allowed to do anything on the file.

[Arnd Bergmann] include <linux/pagemap.h> for PAGE_CACHE_SIZE (used by
MAX_LFS_FILESIZE definition).
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>

We copy i_uid and i_gid of underlying inode into overlayfs inode.  Except
for the root inode.

Fix this omission.
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Cc: <stable@vger.kernel.org>

The overlayfs file system is not recognized by programs
like tail because the magic number is not in standard header location.

Move it so that the value will propagate on for the GNU library
and utilities. Needs to go in the fstatfs manual page as well.
Signed-off-by: NStephen Hemminger <stephen@networkplumber.org>
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>

Add mount option "default_permissions" to alter the way permissions are
calculated.

Without this option and prior to this patch permissions were calculated by
underlying lower or upper filesystem.

With this option the permissions are calculated by overlayfs based on the
file owner, group and mode bits.

This has significance for example when a read-only exported NFS filesystem
is used as a lower layer.  In this case the underlying NFS filesystem will
reply with EROFS, in which case all we know is that the filesystem is
read-only.  But that's not what we are interested in, we are interested in
whether the access would be allowed if the filesystem wasn't read-only; the
server doesn't tell us that, and would need updating at various levels,
which doesn't seem practicable.
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>

This fixes memory leak after umount.

Kmemleak report:

unreferenced object 0xffff8800ba791010 (size 8):
  comm "mount", pid 2394, jiffies 4294996294 (age 53.920s)
  hex dump (first 8 bytes):
    20 1c 13 02 00 88 ff ff                           .......
  backtrace:
    [<ffffffff811f8cd4>] create_object+0x124/0x2c0
    [<ffffffff817a059b>] kmemleak_alloc+0x7b/0xc0
    [<ffffffff811dffe6>] __kmalloc+0x106/0x340
    [<ffffffffa0152bfc>] ovl_fill_super+0x55c/0x9b0 [overlay]
    [<ffffffff81200ac4>] mount_nodev+0x54/0xa0
    [<ffffffffa0152118>] ovl_mount+0x18/0x20 [overlay]
    [<ffffffff81201ab3>] mount_fs+0x43/0x170
    [<ffffffff81220d34>] vfs_kern_mount+0x74/0x170
    [<ffffffff812233ad>] do_mount+0x22d/0xdf0
    [<ffffffff812242cb>] SyS_mount+0x7b/0xc0
    [<ffffffff817b6bee>] entry_SYSCALL_64_fastpath+0x12/0x76
    [<ffffffffffffffff>] 0xffffffffffffffff
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Fixes: dd662667 ("ovl: add mutli-layer infrastructure")
Cc: <stable@vger.kernel.org> # v4.0+

This fixes small memory leak after mount.

Kmemleak report:

unreferenced object 0xffff88003683fe00 (size 16):
  comm "mount", pid 2029, jiffies 4294909563 (age 33.380s)
  hex dump (first 16 bytes):
    20 27 1f bb 00 88 ff ff 40 4b 0f 36 02 88 ff ff   '......@K.6....
  backtrace:
    [<ffffffff811f8cd4>] create_object+0x124/0x2c0
    [<ffffffff817a059b>] kmemleak_alloc+0x7b/0xc0
    [<ffffffff811dffe6>] __kmalloc+0x106/0x340
    [<ffffffffa01b7a29>] ovl_fill_super+0x389/0x9a0 [overlay]
    [<ffffffff81200ac4>] mount_nodev+0x54/0xa0
    [<ffffffffa01b7118>] ovl_mount+0x18/0x20 [overlay]
    [<ffffffff81201ab3>] mount_fs+0x43/0x170
    [<ffffffff81220d34>] vfs_kern_mount+0x74/0x170
    [<ffffffff812233ad>] do_mount+0x22d/0xdf0
    [<ffffffff812242cb>] SyS_mount+0x7b/0xc0
    [<ffffffff817b6bee>] entry_SYSCALL_64_fastpath+0x12/0x76
    [<ffffffffffffffff>] 0xffffffffffffffff
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: NMiklos Szeredi <miklos@szeredi.hu>
Fixes: a78d9f0d ("ovl: support multiple lower layers")
Cc: <stable@vger.kernel.org> # v4.0+

Many file systems that implement the show_options hook fail to correctly
escape their output which could lead to unescaped characters (e.g.  new
lines) leaking into /proc/mounts and /proc/[pid]/mountinfo files.  This
could lead to confusion, spoofed entries (resulting in things like
systemd issuing false d-bus "mount" notifications), and who knows what
else.  This looks like it would only be the root user stepping on
themselves, but it's possible weird things could happen in containers or
in other situations with delegated mount privileges.

Here's an example using overlay with setuid fusermount trusting the
contents of /proc/mounts (via the /etc/mtab symlink).  Imagine the use
of "sudo" is something more sneaky:

  $ BASE="ovl"
  $ MNT="$BASE/mnt"
  $ LOW="$BASE/lower"
  $ UP="$BASE/upper"
  $ WORK="$BASE/work/ 0 0
  none /proc fuse.pwn user_id=1000"
  $ mkdir -p "$LOW" "$UP" "$WORK"
  $ sudo mount -t overlay -o "lowerdir=$LOW,upperdir=$UP,workdir=$WORK" none /mnt
  $ cat /proc/mounts
  none /root/ovl/mnt overlay rw,relatime,lowerdir=ovl/lower,upperdir=ovl/upper,workdir=ovl/work/ 0 0
  none /proc fuse.pwn user_id=1000 0 0
  $ fusermount -u /proc
  $ cat /proc/mounts
  cat: /proc/mounts: No such file or directory

This fixes the problem by adding new seq_show_option and
seq_show_option_n helpers, and updating the vulnerable show_option
handlers to use them as needed.  Some, like SELinux, need to be open
coded due to unusual existing escape mechanisms.

[akpm@linux-foundation.org: add lost chunk, per Kees]
[keescook@chromium.org: seq_show_option should be using const parameters]
Signed-off-by: NKees Cook <keescook@chromium.org>
Acked-by: NSerge Hallyn <serge.hallyn@canonical.com>
Acked-by: NJan Kara <jack@suse.com>
Acked-by: NPaul Moore <paul@paul-moore.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: NKees Cook <keescook@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Allow filesystems with .d_revalidate as lower layer(s), but not as upper
layer.

For local filesystems the rule was that modifications on the layers
directly while being part of the overlay results in undefined behavior.

This can easily be extended to distributed filesystems: we assume the tree
used as lower layer is static, which means ->d_revalidate() should always
return "1".  If that is not the case, return -ESTALE, don't try to work
around the modification.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

NFS and other distributed filesystems may place automount points in the
tree.  Previoulsy overlayfs refused to mount such filesystems types (based
on the existence of the .d_automount callback), even if the actual export
didn't have any automount points.

It cannot be determined in advance whether the filesystem has automount
points or not.  The solution is to allow fs with .d_automount but refuse to
traverse any automount points encountered.
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Make file->f_path always point to the overlay dentry so that the path in
/proc/pid/fd is correct and to ensure that label-based LSMs have access to the
overlay as well as the underlay (path-based LSMs probably don't need it).

Using my union testsuite to set things up, before the patch I see:

	[root@andromeda union-testsuite]# bash 5</mnt/a/foo107
	[root@andromeda union-testsuite]# ls -l /proc/$$/fd/
	...
	lr-x------. 1 root root 64 Jun  5 14:38 5 -> /a/foo107
	[root@andromeda union-testsuite]# stat /mnt/a/foo107
	...
	Device: 23h/35d Inode: 13381       Links: 1
	...
	[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
	...
	Device: 23h/35d Inode: 13381       Links: 1
	...

After the patch:

	[root@andromeda union-testsuite]# bash 5</mnt/a/foo107
	[root@andromeda union-testsuite]# ls -l /proc/$$/fd/
	...
	lr-x------. 1 root root 64 Jun  5 14:22 5 -> /mnt/a/foo107
	[root@andromeda union-testsuite]# stat /mnt/a/foo107
	...
	Device: 23h/35d Inode: 40346       Links: 1
	...
	[root@andromeda union-testsuite]# stat -L /proc/$$/fd/5
	...
	Device: 23h/35d Inode: 40346       Links: 1
	...

Note the change in where /proc/$$/fd/5 points to in the ls command.  It was
pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107
(which is correct).

The inode accessed, however, is the lower layer.  The union layer is on device
25h/37d and the upper layer on 24h/36d.
Signed-off-by: NDavid Howells <dhowells@redhat.com>
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+

After importing multi-lower layer support, users could mount a r/o
partition as the left most lowerdir instead of using it as upperdir.
And a r/o upperdir may cause an error like

	overlayfs: failed to create directory ./workdir/work

during mount.

This patch check the *s_flags* of upper fs and return an error if
it is a r/o partition. The checking of *upper_mnt->mnt_sb->s_flags*
can be removed now.

This patch also remove

	/* FIXME: workdir is not needed for a R/O mount */

from ovl_fill_super() because:

1) for upper fs r/o case
Setting a r/o partition as upper is prevented, no need to care about
workdir in this case.

2) for "mount overlay -o ro" with a r/w upper fs case
Users could remount overlayfs to r/w in this case, so workdir should
not be omitted.
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Recently multi-lower layer mount support allow upperdir and workdir
to be omitted, then cause overlayfs can be mount with only one
lowerdir directory. This action make no sense and have potential risk.

This patch check the total number of lower directories to prevent
mounting overlayfs with only one directory.

Also, an error message is added to indicate lower directories exceed
OVL_MAX_STACK limit.
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Overlayfs should print an error message if an incorrect mount option
is caught like other filesystems.

After this patch, improper option input could be clearly known.
Reported-by: NFabian Sturm <fabian.sturm@aduu.de>
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Overlayfs should be mounted read-only when upper-fs is read-only or nonexistent.
But now it can be remounted read-write and this can cause kernel panic.
So we should prevent read-write remount when the above situation happens.
Signed-off-by: NSeunghun Lee <waydi1@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

Current multi-layer support overlayfs has a regression in
.lookup(). If there is a directory in upperdir and a regular
file has same name in lowerdir in a merged directory, lower
file is hidden and upper directory is set to opaque in former
case. But it is changed in present code.

In lowerdir lookup path, if a found inode is not directory,
the type checking of previous inode is missing. This inode
will be copied to the lowerstack of ovl_entry directly.

That will lead to several wrong conditions, for example,
the reading of the directory in upperdir may return an error
like:

   ls: reading directory .: Not a directory

This patch makes the lowerdir lookup path check the opaque
for non-directory file too.
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>

The function ovl_fill_super() in recently multi-layer support
version will incorrectly return 0 at error handling path and
then cause kernel panic.

This failure can be reproduced by mounting a overlayfs with
upperdir and workdir in different mounts.

And also, If the memory allocation of *lower_mnt* fail, this
function may return an zero either.

This patch fix this problem by setting *err* to proper error
number before jumping to error handling path.
Signed-off-by: Nhujianyang <hujianyang@huawei.com>
Signed-off-by: NMiklos Szeredi <mszeredi@suse.cz>