[PATCH] MIPS: Loongson64: env: Check UARTs passed by LEFI cautiously

[Rong Zhang]

Some firmware does not set nr_uarts properly and passes empty items.
Iterate at most min(system->nr_uarts, MAX_UARTS) items to prevent
out-of-bounds access, and ignore UARTs with addr 0 silently.

Meanwhile, our DT only works with UPIO_MEM but theoretically firmware
may pass other IO types, so explicitly check against that.

Tested on Loongson-LS3A4000-7A1000-NUC-SE.

Fixes: 3989ed418483 ("MIPS: Loongson64: env: Fixup serial clock-frequency when using LEFI")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Rong Zhang <rongrong@xxxxxxxxxxxxxxxxx>
---
 arch/mips/loongson64/env.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/arch/mips/loongson64/env.c b/arch/mips/loongson64/env.c
index 11ddf02d6a15..c6b99b3740ea 100644
--- a/arch/mips/loongson64/env.c
+++ b/arch/mips/loongson64/env.c
@@ -17,8 +17,10 @@
 #include <linux/dma-map-ops.h>
 #include <linux/export.h>
 #include <linux/libfdt.h>
+#include <linux/minmax.h>
 #include <linux/pci_ids.h>
 #include <linux/string_choices.h>
+#include <linux/serial_core.h>
 #include <asm/bootinfo.h>
 #include <loongson.h>
 #include <boot_param.h>
@@ -106,9 +108,23 @@ static void __init lefi_fixup_fdt(struct system_loongson *system)
 
 	is_loongson64g = (read_c0_prid() & PRID_IMP_MASK) == PRID_IMP_LOONGSON_64G;
 
-	for (i = 0; i < system->nr_uarts; i++) {
+	for (i = 0; i < min(system->nr_uarts, MAX_UARTS); i++) {
 		uartdev = &system->uarts[i];
 
+		/*
+		 * Some firmware does not set nr_uarts properly and passes empty
+		 * items. Ignore them silently.
+		 */
+		if (uartdev->uart_base == 0)
+			continue;
+
+		/* Our DT only works with UPIO_MEM. */
+		if (uartdev->iotype != UPIO_MEM) {
+			pr_warn("Ignore UART 0x%llx with iotype %u passed by firmware\n",
+				uartdev->uart_base, uartdev->iotype);
+			continue;
+		}
+
 		ret = lefi_fixup_fdt_serial(fdt_buf, uartdev->uart_base,
 					    uartdev->uartclk);
 		/*

base-commit: 69237f8c1f69112cca7388af7fab6d0ee45a2525
-- 
2.53.0