From 773ad7304837ec20a030522ca57439a2f7f993c2 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Wed, 17 Jun 2020 09:57:11 +0300
Subject: [PATCH] ovl: relax WARN_ON() when decoding lower directory file
 handle
Git-commit: 124c2de2c0aee96271e4ddab190083d8aa7aa71a
Patch-mainline: v5.8-rc6
References: bsc#1184176

Decoding a lower directory file handle to overlay path with cold
inode/dentry cache may go as follows:

1. Decode real lower file handle to lower dir path
2. Check if lower dir is indexed (was copied up)
3. If indexed, get the upper dir path from index
4. Lookup upper dir path in overlay
5. If overlay path found, verify that overlay lower is the lower dir
   from step 1

On failure to verify step 5 above, user will get an ESTALE error and a
WARN_ON will be printed.

A mismatch in step 5 could be a result of lower directory that was renamed
while overlay was offline, after that lower directory has been copied up
and indexed.

This is a scripted reproducer based on xfstest overlay/052:

  # Create lower subdir
  create_dirs
  create_test_files $lower/lowertestdir/subdir
  mount_dirs
  # Copy up lower dir and encode lower subdir file handle
  touch $SCRATCH_MNT/lowertestdir
  test_file_handles $SCRATCH_MNT/lowertestdir/subdir -p -o $tmp.fhandle
  # Rename lower dir offline
  unmount_dirs
  mv $lower/lowertestdir $lower/lowertestdir.new/
  mount_dirs
  # Attempt to decode lower subdir file handle
  test_file_handles $SCRATCH_MNT -p -i $tmp.fhandle

Since this WARN_ON() can be triggered by user we need to relax it.

Fixes: 4b91c30a5a19 ("ovl: lookup connected ancestor of dir in inode cache")
Cc: <stable@vger.kernel.org> # v4.16+
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Acked-by: David Disseldorp <ddiss@suse.de>

---
 fs/overlayfs/export.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 73c9775215b3..11dd8177770d 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -482,7 +482,7 @@ static struct dentry *ovl_lookup_real_inode(struct super_block *sb,
 	if (IS_ERR_OR_NULL(this))
 		return this;
 
-	if (WARN_ON(ovl_dentry_real_at(this, layer->idx) != real)) {
+	if (ovl_dentry_real_at(this, layer->idx) != real) {
 		dput(this);
 		this = ERR_PTR(-EIO);
 	}
-- 
2.26.2