OSS-Fuzz: Add new fuzzer targets layout processing

Signed-off-by: Arthur Chan <arthur.chan@adalogics.com>

Makefile.am

@@ -257,7 +257,8 @@ check_PROGRAMS = \
 	fuzz/input-fuzzer \
 	fuzz/cmd-parse-fuzzer \
 	fuzz/format-fuzzer \
-	fuzz/style-fuzzer
+	fuzz/style-fuzzer \
+	fuzz/layout-fuzzer
 fuzz_input_fuzzer_LDFLAGS = $(FUZZING_LIBS)
 fuzz_input_fuzzer_LDADD = $(LDADD) $(tmux_OBJECTS)
 fuzz_cmd_parse_fuzzer_LDFLAGS = $(FUZZING_LIBS)
@@ -266,6 +267,8 @@ fuzz_format_fuzzer_LDFLAGS = $(FUZZING_LIBS)
 fuzz_format_fuzzer_LDADD = $(LDADD) $(tmux_OBJECTS)
 fuzz_style_fuzzer_LDFLAGS = $(FUZZING_LIBS)
 fuzz_style_fuzzer_LDADD = $(LDADD) $(tmux_OBJECTS)
+fuzz_layout_fuzzer_LDFLAGS = $(FUZZING_LIBS)
+fuzz_layout_fuzzer_LDADD = $(LDADD) $(tmux_OBJECTS)
 endif
 
 # Install tmux.1 in the right format.

fuzz/layout-fuzzer.c

@@ -0,0 +1,111 @@
+/*
+ * Copyright (c) 2026 Arthur Chan <arthur.chan@adalogics.com>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
+ * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
+ * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * Fuzz the custom layout parser.
+ *
+ * A layout string such as "bb62,80x24,0,0{40x24,0,0,1,39x24,41,0,2}" is
+ * accepted by select-layout and is what tmux stores and restores for a
+ * window, so it is parsed from configuration and from commands. It drives
+ * layout-custom.c (the string parser and the checksum), then layout.c, which
+ * resizes and assigns the cells.
+ *
+ * layout_parse() refuses a window with no panes, and refuses a layout whose
+ * cell count is smaller than the pane count, so the window is given a fixed
+ * number of panes. The count is fixed rather than derived from the input, so
+ * a mutation always means a different layout string.
+ */
+
+#include <sys/types.h>
+
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "tmux.h"
+
+#define FUZZER_MAXLEN 1024
+#define FUZZER_PANES 4
+
+struct event_base	*libevent;
+
+int
+LLVMFuzzerTestOneInput(const u_char *data, size_t size)
+{
+	struct window		*w;
+	struct window_pane	*wp;
+	char			*buf, *cause = NULL, *dump;
+	u_int			 i;
+
+	if (size == 0 || size > FUZZER_MAXLEN)
+		return 0;
+
+	/* layout_parse() takes a C string. */
+	buf = malloc(size + 1);
+	if (buf == NULL)
+		return 0;
+	memcpy(buf, data, size);
+	buf[size] = '\0';
+
+	w = window_create(80, 24, 0, 0);
+	if (w == NULL) {
+		free(buf);
+		return 0;
+	}
+	window_add_ref(w, __func__);
+
+	for (i = 0; i < FUZZER_PANES; i++) {
+		wp = window_add_pane(w, NULL, 0, 0);
+		if (w->active == NULL)
+			w->active = wp;
+	}
+
+	if (layout_parse(w, buf, &cause) == 0) {
+		dump = layout_dump(w, w->layout_root, 1);
+		free(dump);
+	}
+	free(cause);
+
+	window_remove_ref(w, __func__);
+
+	free(buf);
+	return 0;
+}
+
+int
+LLVMFuzzerInitialize(__unused int *argc, __unused char ***argv)
+{
+	const struct options_table_entry	*oe;
+
+	global_environ = environ_create();
+	global_options = options_create(NULL);
+	global_s_options = options_create(NULL);
+	global_w_options = options_create(NULL);
+	for (oe = options_table; oe->name != NULL; oe++) {
+		if (oe->scope & OPTIONS_TABLE_SERVER)
+			options_default(global_options, oe);
+		if (oe->scope & OPTIONS_TABLE_SESSION)
+			options_default(global_s_options, oe);
+		if (oe->scope & OPTIONS_TABLE_WINDOW)
+			options_default(global_w_options, oe);
+	}
+
+	libevent = osdep_event_init();
+
+	socket_path = xstrdup("dummy");
+
+	return 0;
+}

fuzz/layout-fuzzer.dict

@@ -0,0 +1,17 @@
+# tmux custom layout strings: "<checksum>,<sx>x<sy>,<x>,<y>{...}" / "[...]"
+","
+"x"
+"{"
+"}"
+"["
+"]"
+"0"
+"1"
+"80x24,0,0"
+"40x24,0,0"
+"bb62,"
+"cafe,"
+",0,0,0"
+",0,0{"
+",0,0["
+"@"

fuzz/layout-fuzzer.options

@@ -0,0 +1,2 @@
+[libfuzzer]
+max_len = 1024