[PATCH v2] powerpc/legacy_serial: Fix UBSAN: array-index-out-of-bounds

[Michael Ellerman <mpe@ellerman.id.au>]

From: Christophe Leroy <christophe.leroy@csgroup.eu>

UBSAN complains when a pointer is calculated with invalid
'legacy_serial_console' index, allthough the index is verified
before dereferencing the pointer.

Fix it by checking 'legacy_serial_console' validity before
calculating pointers.

Fixes: 0bd3f9e953bd ("powerpc/legacy_serial: Use early_ioremap()")
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/kernel/legacy_serial.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

v2: mpe: Just move the assignment of port/info below the check, as
    suggested by Segher.

diff --git a/arch/powerpc/kernel/legacy_serial.c b/arch/powerpc/kernel/legacy_serial.c
index 8b2c1a8553a0..cfc03e016ff2 100644
--- a/arch/powerpc/kernel/legacy_serial.c
+++ b/arch/powerpc/kernel/legacy_serial.c
@@ -356,13 +356,16 @@ static void __init setup_legacy_serial_console(int console)
 
 static int __init ioremap_legacy_serial_console(void)
 {
-	struct legacy_serial_info *info = &legacy_serial_infos[legacy_serial_console];
-	struct plat_serial8250_port *port = &legacy_serial_ports[legacy_serial_console];
+	struct plat_serial8250_port *port;
+	struct legacy_serial_info *info;
 	void __iomem *vaddr;
 
 	if (legacy_serial_console < 0)
 		return 0;
 
+	info = &legacy_serial_infos[legacy_serial_console];
+	port = &legacy_serial_ports[legacy_serial_console];
+
 	if (!info->early_addr)
 		return 0;
 
-- 
2.25.1