[PATCH 4.20 48/92] CIFS: Fix mounts if the client is low on credits

[Greg Kroah-Hartman]

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

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

[ Upstream commit 6a9cbdd1ceca1dc2359ddf082efe61b97c3e752b ]

If the server doesn't grant us at least 3 credits during the mount
we won't be able to complete it because query path info operation
requires 3 credits. Use the cached file handle if possible to allow
the mount to succeed.

Signed-off-by: Pavel Shilovsky <pshilov@xxxxxxxxxxxxx>
Reviewed-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
Signed-off-by: Steve French <stfrench@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 fs/cifs/smb2inode.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/cifs/smb2inode.c b/fs/cifs/smb2inode.c
index a8999f930b22..057d2034209f 100644
--- a/fs/cifs/smb2inode.c
+++ b/fs/cifs/smb2inode.c
@@ -294,6 +294,8 @@ smb2_query_path_info(const unsigned int xid, struct cifs_tcon *tcon,
 	int rc;
 	struct smb2_file_all_info *smb2_data;
 	__u32 create_options = 0;
+	struct cifs_fid fid;
+	bool no_cached_open = tcon->nohandlecache;
 
 	*adjust_tz = false;
 	*symlink = false;
@@ -302,6 +304,21 @@ smb2_query_path_info(const unsigned int xid, struct cifs_tcon *tcon,
 			    GFP_KERNEL);
 	if (smb2_data == NULL)
 		return -ENOMEM;
+
+	/* If it is a root and its handle is cached then use it */
+	if (!strlen(full_path) && !no_cached_open) {
+		rc = open_shroot(xid, tcon, &fid);
+		if (rc)
+			goto out;
+		rc = SMB2_query_info(xid, tcon, fid.persistent_fid,
+				     fid.volatile_fid, smb2_data);
+		close_shroot(&tcon->crfid);
+		if (rc)
+			goto out;
+		move_smb2_info_to_cifs(data, smb2_data);
+		goto out;
+	}
+
 	if (backup_cred(cifs_sb))
 		create_options |= CREATE_OPEN_BACKUP_INTENT;
 
-- 
2.19.1