[PATCH 10/28] of/fdt: Replace strlcat() with snprintf() in early_init_dt_scan_chosen()

When CONFIG_CMDLINE_EXTEND is enabled, early_init_dt_scan_chosen() uses
two strlcat() calls to append a space and CONFIG_CMDLINE to the command
line buffer.

In preparation for removing the deprecated strlcat() API[1], replace the
strlcat() calls with a single snprintf() call using the existing string
length.

Additionally, check for a NULL initial_boot_params pointer and jump to
"handle_cmdline" so that CONFIG_CMDLINE handling still occurs without
dereferencing a NULL FDT pointer in fdt_path_offset().

Link: https://github.com/KSPP/linux/issues/370 [1]
Cc: codemender-patching+linux@google.com
Assisted-by: Assistant:Claude-3.5-Sonnet [editor_update_file, shell_command_run]
Signed-off-by: Bill Wendling <morbo@google.com>
---
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---
 drivers/of/fdt.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
index a64afc3ded3d..311021a83f03 100644
--- a/drivers/of/fdt.c
+++ b/drivers/of/fdt.c

@@ -1095,6 +1095,9 @@ int __init early_init_dt_scan_chosen(char *cmdline)
 	const void *rng_seed;
 	const void *fdt = initial_boot_params;
 
+	if (!fdt)
+		goto handle_cmdline;
+
 	node = fdt_path_offset(fdt, "/chosen");
 	if (node < 0)
 		node = fdt_path_offset(fdt, "/chosen@0");

@@ -1133,8 +1136,12 @@ int __init early_init_dt_scan_chosen(char *cmdline)
 	 */
 #ifdef CONFIG_CMDLINE
 #if defined(CONFIG_CMDLINE_EXTEND)
-	strlcat(cmdline, " ", COMMAND_LINE_SIZE);
-	strlcat(cmdline, CONFIG_CMDLINE, COMMAND_LINE_SIZE);
+	{
+		size_t len = strlen(cmdline);
+
+		if (len < COMMAND_LINE_SIZE)
+			snprintf(cmdline + len, COMMAND_LINE_SIZE - len, " %s", CONFIG_CMDLINE);
+	}
 #elif defined(CONFIG_CMDLINE_FORCE)
 	strscpy(cmdline, CONFIG_CMDLINE, COMMAND_LINE_SIZE);
 #else

-- 
2.55.0.1032.g73a4cd73de-goog