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[PATCH 4.4 22/50] ovl: ignore lower entries when checking purity of non-directory entries

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4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <koct9i@gmail.com>

commit 45d11738969633ec07ca35d75d486bf2d8918df6 upstream.

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: Konstantin Khlebnikov <koct9i@gmail.com>
Reported-by: Viktor Stanchev <me@viktorstanchev.com>
Suggested-by: Vivek Goyal <vgoyal@redhat.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=109611
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/overlayfs/dir.c   |    7 +++++++
 fs/overlayfs/super.c |   12 +++++++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -903,6 +903,13 @@ static int ovl_rename2(struct inode *old
 	if (!overwrite && new_is_dir && !old_opaque && new_opaque)
 		ovl_remove_opaque(newdentry);
 
+	/*
+	 * Old dentry now lives in different location. Dentries in
+	 * lowerstack are stale. We cannot drop them here because
+	 * access to them is lockless. This could be only pure upper
+	 * or opaque directory - numlower is zero. Or upper non-dir
+	 * entry - its pureness is tracked by flag opaque.
+	 */
 	if (old_opaque != new_opaque) {
 		ovl_dentry_set_opaque(old, new_opaque);
 		if (!overwrite)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -76,12 +76,14 @@ enum ovl_path_type ovl_path_type(struct
 	if (oe->__upperdentry) {
 		type = __OVL_PATH_UPPER;
 
-		if (oe->numlower) {
-			if (S_ISDIR(dentry->d_inode->i_mode))
-				type |= __OVL_PATH_MERGE;
-		} else if (!oe->opaque) {
+		/*
+		 * Non-dir dentry can hold lower dentry from previous
+		 * location. Its purity depends only on opaque flag.
+		 */
+		if (oe->numlower && S_ISDIR(dentry->d_inode->i_mode))
+			type |= __OVL_PATH_MERGE;
+		else if (!oe->opaque)
 			type |= __OVL_PATH_PURE;
-		}
 	} else {
 		if (oe->numlower > 1)
 			type |= __OVL_PATH_MERGE;

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[PATCH 4.4 00/50] 4.4.6-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 11/50] KVM: MMU: fix reserved bit check for ept=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 47/50] MIPS: smp.c: Fix uninitialised temp_foreign_map Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 10/50] KVM: MMU: fix ept=0/pte.u=1/pte.w=0/CR0.WP=0/CR4.SMEP=1/EFER.NX=0 combo Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 14/50] tracing: Fix check for cpu online when event is disabled Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:10 +0100
  [PATCH 4.4 39/50] Revert "drm/radeon/pm: adjust display configuration after powerstate" Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 30/50] mac80211: minstrel_ht: set default tx aggregation timeout to 0 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
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  [PATCH 4.4 40/50] powerpc: Fix dedotify for binutils >= 2.26 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 28/50] mac80211: minstrel: Change expected throughput unit back to Kbps Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 33/50] mac80211: Fix Public Action frame RX in AP mode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 41/50] powerpc/powernv: Add a kmsg_dumper that flushes console output on panic Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 29/50] mac80211: fix use of uninitialised values in RX aggregation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 22/50] ovl: ignore lower entries when checking purity of non-directory entries Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 04/50] ARM: OMAP2+: hwmod: Introduce ti,no-idle dt property Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 45/50] ovl: fix getcwd() failure after unsuccessful rmdir Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 23/50] ovl: fix working on distributed fs as lower layer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
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  [PATCH 4.4 24/50] wext: fix message delay/ordering Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
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  [PATCH 4.4 44/50] ovl: copy new uid/gid into overlayfs runtime inode Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 35/50] x86/mm: Fix slow_virt_to_phys() for X86_PAE again Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
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  [PATCH 4.4 34/50] gpu: ipu-v3: Do not bail out on missing optional port nodes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:20 +0100
  [PATCH 4.4 15/50] dmaengine: at_xdmac: fix residue computation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
  [PATCH 4.4 25/50] cfg80211/wext: fix message ordering Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
  [PATCH 4.4 20/50] ASoC: wm8994: Fix enum ctl accesses in a wrong type Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-14 19:30 +0100
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  Re: [PATCH 4.4 00/50] 4.4.6-stable review Guenter Roeck <linux@roeck-us.net> - 2016-03-15 03:40 +0100
    Re: [PATCH 4.4 00/50] 4.4.6-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-03-16 16:50 +0100

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