[PATCH 4.18 081/145] ovl: fix wrong use of impure dir cache in ovl_iterate()

[Greg Kroah-Hartman]

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

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

From: Amir Goldstein <amir73il@xxxxxxxxx>

commit 67810693077afc1ebf9e1646af300436cb8103c2 upstream.

Only upper dir can be impure, but if we are in the middle of
iterating a lower real dir, dir could be copied up and marked
impure. We only want the impure cache if we started iterating
a real upper dir to begin with.

Aditya Kali reported that the following reproducer hits the
WARN_ON(!cache->refcount) in ovl_get_cache():

 docker run --rm drupal:8.5.4-fpm-alpine \
    sh -c 'cd /var/www/html/vendor/symfony && \
           chown -R www-data:www-data . && ls -l .'

Reported-by: Aditya Kali <adityakali@xxxxxxxxxx>
Tested-by: Aditya Kali <adityakali@xxxxxxxxxx>
Fixes: 4edb83bb1041 ('ovl: constant d_ino for non-merge dirs')
Cc: <stable@xxxxxxxxxxxxxxx> # v4.14
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/overlayfs/readdir.c |   19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -668,6 +668,21 @@ static int ovl_fill_real(struct dir_cont
 	return orig_ctx->actor(orig_ctx, name, namelen, offset, ino, d_type);
 }
 
+static bool ovl_is_impure_dir(struct file *file)
+{
+	struct ovl_dir_file *od = file->private_data;
+	struct inode *dir = d_inode(file->f_path.dentry);
+
+	/*
+	 * Only upper dir can be impure, but if we are in the middle of
+	 * iterating a lower real dir, dir could be copied up and marked
+	 * impure. We only want the impure cache if we started iterating
+	 * a real upper dir to begin with.
+	 */
+	return od->is_upper && ovl_test_flag(OVL_IMPURE, dir);
+
+}
+
 static int ovl_iterate_real(struct file *file, struct dir_context *ctx)
 {
 	int err;
@@ -696,7 +711,7 @@ static int ovl_iterate_real(struct file
 		rdt.parent_ino = stat.ino;
 	}
 
-	if (ovl_test_flag(OVL_IMPURE, d_inode(dir))) {
+	if (ovl_is_impure_dir(file)) {
 		rdt.cache = ovl_cache_get_impure(&file->f_path);
 		if (IS_ERR(rdt.cache))
 			return PTR_ERR(rdt.cache);
@@ -727,7 +742,7 @@ static int ovl_iterate(struct file *file
 		 */
 		if (ovl_xino_bits(dentry->d_sb) ||
 		    (ovl_same_sb(dentry->d_sb) &&
-		     (ovl_test_flag(OVL_IMPURE, d_inode(dentry)) ||
+		     (ovl_is_impure_dir(file) ||
 		      OVL_TYPE_MERGE(ovl_path_type(dentry->d_parent))))) {
 			return ovl_iterate_real(file, ctx);
 		}