[ceph] parse_longname(): strrchr() expects NUL-terminated string

... and parse_longname() is not guaranteed that.  That's the reason
why it uses kmemdup_nul() to build the argument for kstrtou64();
the problem is, kstrtou64() is not the only thing that need it.

Just get a NUL-terminated copy of the entire thing and be done
with that...

Fixes: dd66df0 "ceph: add support for encrypted snapshot names"
Tested-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Author: Al Viro

fs/ceph/crypto.c

@@ -215,35 +215,31 @@ static struct inode *parse_longname(const struct inode *parent,
 	struct ceph_client *cl = ceph_inode_to_client(parent);
 	struct inode *dir = NULL;
 	struct ceph_vino vino = { .snap = CEPH_NOSNAP };
-	char *inode_number;
-	char *name_end;
-	int orig_len = *name_len;
+	char *name_end, *inode_number;
 	int ret = -EIO;
-
+	/* NUL-terminate */
+	char *str __free(kfree) = kmemdup_nul(name, *name_len, GFP_KERNEL);
+	if (!str)
+		return ERR_PTR(-ENOMEM);
 	/* Skip initial '_' */
-	name++;
-	name_end = strrchr(name, '_');
+	str++;
+	name_end = strrchr(str, '_');
 	if (!name_end) {
-		doutc(cl, "failed to parse long snapshot name: %s\n", name);
+		doutc(cl, "failed to parse long snapshot name: %s\n", str);
 		return ERR_PTR(-EIO);
 	}
-	*name_len = (name_end - name);
+	*name_len = (name_end - str);
 	if (*name_len <= 0) {
 		pr_err_client(cl, "failed to parse long snapshot name\n");
 		return ERR_PTR(-EIO);
 	}
 
 	/* Get the inode number */
-	inode_number = kmemdup_nul(name_end + 1,
-				   orig_len - *name_len - 2,
-				   GFP_KERNEL);
-	if (!inode_number)
-		return ERR_PTR(-ENOMEM);
+	inode_number = name_end + 1;
 	ret = kstrtou64(inode_number, 10, &vino.ino);
 	if (ret) {
-		doutc(cl, "failed to parse inode number: %s\n", name);
-		dir = ERR_PTR(ret);
-		goto out;
+		doutc(cl, "failed to parse inode number: %s\n", str);
+		return ERR_PTR(ret);
 	}
 
 	/* And finally the inode */
@@ -254,9 +250,6 @@ static struct inode *parse_longname(const struct inode *parent,
 		if (IS_ERR(dir))
 			doutc(cl, "can't find inode %s (%s)\n", inode_number, name);
 	}
-
-out:
-	kfree(inode_number);
 	return dir;
 }