smb3: Fix regression in time handling

Fixes: cb7a69e605 ("cifs: Initialize filesystem timestamp ranges")

Only very old servers (e.g. OS/2 and DOS) did not support
DCE TIME (100 nanosecond granularity).  Fix the checks used
to set minimum and maximum times.

Fixes xfstest generic/258 (on 5.4-rc1 and later)

CC: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>

fs/cifs/cifsfs.c

@@ -169,19 +169,27 @@ cifs_read_super(struct super_block *sb)
 	else
 		sb->s_maxbytes = MAX_NON_LFS;
 
-	/* BB FIXME fix time_gran to be larger for LANMAN sessions */
-	sb->s_time_gran = 100;
-
-	if (tcon->unix_ext) {
+	/* Some very old servers like DOS and OS/2 used 2 second granularity */
+	if ((tcon->ses->server->vals->protocol_id == SMB10_PROT_ID) &&
+	    ((tcon->ses->capabilities &
+	      tcon->ses->server->vals->cap_nt_find) == 0) &&
+	    !tcon->unix_ext) {
+		sb->s_time_gran = 1000000000; /* 1 second is max allowed gran */
+		ts = cnvrtDosUnixTm(cpu_to_le16(SMB_DATE_MIN), 0, 0);
+		sb->s_time_min = ts.tv_sec;
+		ts = cnvrtDosUnixTm(cpu_to_le16(SMB_DATE_MAX),
+				    cpu_to_le16(SMB_TIME_MAX), 0);
+		sb->s_time_max = ts.tv_sec;
+	} else {
+		/*
+		 * Almost every server, including all SMB2+, uses DCE TIME
+		 * ie 100 nanosecond units, since 1601.  See MS-DTYP and MS-FSCC
+		 */
+		sb->s_time_gran = 100;
 		ts = cifs_NTtimeToUnix(0);
 		sb->s_time_min = ts.tv_sec;
 		ts = cifs_NTtimeToUnix(cpu_to_le64(S64_MAX));
 		sb->s_time_max = ts.tv_sec;
-	} else {
-		ts = cnvrtDosUnixTm(cpu_to_le16(SMB_DATE_MIN), 0, 0);
-		sb->s_time_min = ts.tv_sec;
-		ts = cnvrtDosUnixTm(cpu_to_le16(SMB_DATE_MAX), cpu_to_le16(SMB_TIME_MAX), 0);
-		sb->s_time_max = ts.tv_sec;
 	}
 
 	sb->s_magic = CIFS_MAGIC_NUMBER;