command: dupe mode name memory

The hashmap doesn't take ownership of the memory pointer to by these
slices, so we need to dupe them to avoid use-after-free.

 river/Config.zig               | 3 +++
 river/command/declare_mode.zig | 7 +++++--
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/river/Config.zig b/river/Config.zig
index 015d02d..ea45f38 100644
--- a/river/Config.zig
+++ b/river/Config.zig
@@ -61,12 +61,15 @@ pub fn init(self: *Self) !void {
     self.outer_padding = 8;
 
     self.mode_to_id = std.StringHashMap(usize).init(util.gpa);
+    errdefer self.mode_to_id.deinit();
     try self.mode_to_id.putNoClobber("normal", 0);
 
     self.modes = std.ArrayList(std.ArrayList(Mapping)).init(util.gpa);
+    errdefer self.modes.deinit();
     try self.modes.append(std.ArrayList(Mapping).init(util.gpa));
 
     self.float_filter = std.ArrayList([*:0]const u8).init(util.gpa);
+    errdefer self.float_filter.deinit();
 
     // Float views with app_id "float"
     try self.float_filter.append("float");
diff --git a/river/command/declare_mode.zig b/river/command/declare_mode.zig
index 943ede8..06472a9 100644
--- a/river/command/declare_mode.zig
+++ b/river/command/declare_mode.zig
@@ -18,6 +18,7 @@
 const std = @import("std");
 
 const c = @import("../c.zig");
+const util = @import("../util.zig");
 
 const Error = @import("../command.zig").Error;
 const Mapping = @import("../Mapping.zig");
@@ -45,7 +46,9 @@ pub fn declareMode(
         return Error.CommandFailed;
     }
 
-    try config.mode_to_id.putNoClobber(new_mode_name, config.modes.items.len);
-    errdefer _ = config.mode_to_id.remove(new_mode_name);
+    const owned_name = try std.mem.dupe(util.gpa, u8, new_mode_name);
+    errdefer util.gpa.free(owned_name);
+    try config.mode_to_id.putNoClobber(owned_name, config.modes.items.len);
+    errdefer _ = config.mode_to_id.remove(owned_name);
     try config.modes.append(std.ArrayList(Mapping).init(allocator));
 }