NFSD: correctly range-check v4.x minor version when setting versions.

Writing to /proc/fs/nfsd/versions allows individual major versions
and NFSv4 minor versions to be enabled or disabled.

However NFSv4.0 cannot currently be disabled, thought there is no good reason.
Also the minor number is parsed as a 'long' but used as an 'int'
so '4294967297' will be incorrectly treated as '1'.

This patch removes the test on 'minor == 0' and switches to kstrtouint()
to get correct range checking.

When reading from /proc/fs/nfsd/versions, 4.0 is current not reported.
To allow the disabling for v4.0 to be visible, while maintaining
backward compatibility, change code to report "-4.0" if appropriate, but
not "+4.0".
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfsctl.c

@@ -569,8 +569,7 @@ static ssize_t __write_versions(struct file *file, char *buf, size_t size)
 			if (*minorp == '.') {
 				if (num != 4)
 					return -EINVAL;
-				minor = simple_strtoul(minorp+1, NULL, 0);
-				if (minor == 0)
+				if (kstrtouint(minorp+1, 0, &minor) < 0)
 					return -EINVAL;
 				if (nfsd_minorversion(minor, sign == '-' ?
 						     NFSD_CLEAR : NFSD_SET) < 0)
@@ -613,8 +612,13 @@ static ssize_t __write_versions(struct file *file, char *buf, size_t size)
 			tlen += len;
 		}
 	if (nfsd_vers(4, NFSD_AVAIL))
-		for (minor = 1; minor <= NFSD_SUPPORTED_MINOR_VERSION;
+		for (minor = 0; minor <= NFSD_SUPPORTED_MINOR_VERSION;
 		     minor++) {
+			if (minor == 0 && nfsd_minorversion(minor, NFSD_TEST))
+				/* for backward compatibility, don't report
+				 * +4.0
+				 */
+				continue;
 			len = snprintf(buf, remaining, " %c4.%u",
 					(nfsd_vers(4, NFSD_TEST) &&
 					 nfsd_minorversion(minor, NFSD_TEST)) ?