x86/boot: Validate console=uart8250 baud rate to fix early boot hang

When the baud rate is empty, 0, invalid, or overflows to 0 when stored
as an int, the system will hang during early boot because of a division
by zero in early_serial_init().

Fall back to DEFAULT_BAUD when the resulting baud rate is 0 to prevent
an early system hang.

Fixes: ce0aa5dd20e4 ("x86, setup: Make the setup code also accept console=uart8250")
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260713194924.126472-3-thorsten.blum@linux.dev

diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
index 023bf1c3de8b7a1d1d5b22c9dd1c9312ed07ad70..5b83beab89e15085dc4d9ab8828c177881d3f95e 100644 (file)
--- a/arch/x86/boot/early_serial_console.c
+++ b/arch/x86/boot/early_serial_console.c
@@ -117,7 +117,7 @@ static unsigned int probe_baud(int port)
 static void parse_console_uart8250(void)
 {
        char optstr[64], *options;
-       int baud = DEFAULT_BAUD;
+       int baud;
        int port = 0;
 
        /*
@@ -136,10 +136,13 @@ static void parse_console_uart8250(void)
        else
                return;
 
-       if (options && (options[0] == ','))
-               baud = simple_strtoull(options + 1, &options, 0);
-       else
+       if (options && (options[0] == ',')) {
+               baud = simple_strtoull(options + 1, NULL, 0);
+               if (!baud)
+                       baud = DEFAULT_BAUD;
+       } else {
                baud = probe_baud(port);
+       }
 
        if (port)
                early_serial_init(port, baud);