smb3: Fix root directory when server returns inode number of zero

Some servers return inode number zero for the root directory, which
causes ls to display incorrect data (missing "." and "..").

If the server returns zero for the inode number of the root directory,
fake an inode number for it.

Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
CC: Stable <stable@vger.kernel.org>

fs/cifs/cifsglob.h

@@ -1470,6 +1470,7 @@ struct dfs_info3_param {
 #define CIFS_FATTR_NEED_REVAL		0x4
 #define CIFS_FATTR_INO_COLLISION	0x8
 #define CIFS_FATTR_UNKNOWN_NLINK	0x10
+#define CIFS_FATTR_FAKE_ROOT_INO	0x20
 
 struct cifs_fattr {
 	u32		cf_flags;

fs/cifs/inode.c

@@ -707,6 +707,18 @@ cgfi_exit:
 	return rc;
 }
 
+/* Simple function to return a 64 bit hash of string.  Rarely called */
+static __u64 simple_hashstr(const char *str)
+{
+	const __u64 hash_mult =  1125899906842597L; /* a big enough prime */
+	__u64 hash = 0;
+
+	while (*str)
+		hash = (hash + (__u64) *str++) * hash_mult;
+
+	return hash;
+}
+
 int
 cifs_get_inode_info(struct inode **inode, const char *full_path,
 		    FILE_ALL_INFO *data, struct super_block *sb, int xid,
@@ -816,6 +828,14 @@ cifs_get_inode_info(struct inode **inode, const char *full_path,
 						 tmprc);
 					fattr.cf_uniqueid = iunique(sb, ROOT_I);
 					cifs_autodisable_serverino(cifs_sb);
+				} else if ((fattr.cf_uniqueid == 0) &&
+						strlen(full_path) == 0) {
+					/* some servers ret bad root ino ie 0 */
+					cifs_dbg(FYI, "Invalid (0) inodenum\n");
+					fattr.cf_flags |=
+						CIFS_FATTR_FAKE_ROOT_INO;
+					fattr.cf_uniqueid =
+						simple_hashstr(tcon->treeName);
 				}
 			}
 		} else
@@ -832,6 +852,16 @@ cifs_get_inode_info(struct inode **inode, const char *full_path,
 				&fattr.cf_uniqueid, data);
 			if (tmprc)
 				fattr.cf_uniqueid = CIFS_I(*inode)->uniqueid;
+			else if ((fattr.cf_uniqueid == 0) &&
+					strlen(full_path) == 0) {
+				/*
+				 * Reuse existing root inode num since
+				 * inum zero for root causes ls of . and .. to
+				 * not be returned
+				 */
+				cifs_dbg(FYI, "Srv ret 0 inode num for root\n");
+				fattr.cf_uniqueid = CIFS_I(*inode)->uniqueid;
+			}
 		} else
 			fattr.cf_uniqueid = CIFS_I(*inode)->uniqueid;
 	}
@@ -893,6 +923,9 @@ cifs_get_inode_info(struct inode **inode, const char *full_path,
 	}
 
 cgii_exit:
+	if ((*inode) && ((*inode)->i_ino == 0))
+		cifs_dbg(FYI, "inode number of zero returned\n");
+
 	kfree(buf);
 	cifs_put_tlink(tlink);
 	return rc;