printk: Check valid console index for preferred console

Let's check for valid console index values for preferred console to avoid
bogus console index numbers from kernel command line.

Let's also return an error for negative index numbers for the preferred
console. Unlike for device drivers, a negative index is not valid for the
preferred console.

Let's also constify idx while at it.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20231012064300.50221-1-tony@atomide.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/linux/console.h b/include/linux/console.h
index 5ff6f11c47b18413ace14390037c518a70e5d68b..1be13c9695e0d8c0c408d54493c02a7de279e114 100644 (file)
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -347,7 +347,7 @@ enum con_flush_mode {
        CONSOLE_REPLAY_ALL,
 };
 
-extern int add_preferred_console(char *name, int idx, char *options);
+extern int add_preferred_console(char *name, const short idx, char *options);
 extern void console_force_preferred_locked(struct console *con);
 extern void register_console(struct console *);
 extern int unregister_console(struct console *);

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 0b3af1529778c0ffe58675af216faeba434aba5e..b16c0bab88c66a319091a3e467fd9f35f54faa49 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2404,12 +2404,20 @@ static void set_user_specified(struct console_cmdline *c, bool user_specified)
        console_set_on_cmdline = 1;
 }
 
-static int __add_preferred_console(char *name, int idx, char *options,
+static int __add_preferred_console(char *name, const short idx, char *options,
                                   char *brl_options, bool user_specified)
 {
        struct console_cmdline *c;
        int i;
 
+       /*
+        * We use a signed short index for struct console for device drivers to
+        * indicate a not yet assigned index or port. However, a negative index
+        * value is not valid for preferred console.
+        */
+       if (idx < 0)
+               return -EINVAL;
+
        /*
         *      See if this tty is not yet registered, and
         *      if we have a slot free.
@@ -2513,7 +2521,7 @@ __setup("console=", console_setup);
  * commonly to provide a default console (ie from PROM variables) when
  * the user has not supplied one.
  */
-int add_preferred_console(char *name, int idx, char *options)
+int add_preferred_console(char *name, const short idx, char *options)
 {
        return __add_preferred_console(name, idx, options, NULL, false);
 }