ovl: do not encode lower fh with upper sb_writers held

When lower fs is a nested overlayfs, calling encode_fh() on a lower
directory dentry may trigger copy up and take sb_writers on the upper fs
of the lower nested overlayfs.

The lower nested overlayfs may have the same upper fs as this overlayfs,
so nested sb_writers lock is illegal.

Move all the callers that encode lower fh to before ovl_want_write().

Signed-off-by: Amir Goldstein <amir73il@gmail.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 12156e2091ad..f8455fcb8b07 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -1013,12 +1013,18 @@ static void ovl_cleanup_index(struct dentry *dentry)
 	struct dentry *index = NULL;
 	struct inode *inode;
 	struct qstr name = { };
+	bool got_write = false;
 	int err;
 
 	err = ovl_get_index_name(ofs, lowerdentry, &name);
 	if (err)
 		goto fail;
 
+	err = ovl_want_write(dentry);
+	if (err)
+		goto fail;
+
+	got_write = true;
 	inode = d_inode(upperdentry);
 	if (!S_ISDIR(inode->i_mode) && inode->i_nlink != 1) {
 		pr_warn_ratelimited("cleanup linked index (%pd2, ino=%lu, nlink=%u)\n",
@@ -1056,6 +1062,8 @@ static void ovl_cleanup_index(struct dentry *dentry)
 		goto fail;
 
 out:
+	if (got_write)
+		ovl_drop_write(dentry);
 	kfree(name.name);
 	dput(index);
 	return;
@@ -1135,6 +1143,8 @@ void ovl_nlink_end(struct dentry *dentry)
 {
 	struct inode *inode = d_inode(dentry);
 
+	ovl_drop_write(dentry);
+
 	if (ovl_test_flag(OVL_INDEX, inode) && inode->i_nlink == 0) {
 		const struct cred *old_cred;
 
@@ -1143,7 +1153,6 @@ void ovl_nlink_end(struct dentry *dentry)
 		revert_creds(old_cred);
 	}
 
-	ovl_drop_write(dentry);
 	ovl_inode_unlock(inode);
 }