linux-kernel - [PATCH] serial: sh-sci: Fix use-after-free on subsequent port startup

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Date:   Tue, 17 Jul 2018 10:58:10 +0200
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Chris Brandt <chris.brandt@...esas.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>
Cc:     linux-serial@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] serial: sh-sci: Fix use-after-free on subsequent port startup

sci_request_irq() checks port->irqstr[j] for a NULL pointer, to decide
if a fallback interrupt name string should be allocated or not.

While this string is freed during port shutdown, the pointer is not
zeroed.  Hence on a subsequent startup of the port, it will still be
pointing to the freed memory, leading to e.g.

    WARNING: CPU: 0 PID: 404 at fs/proc/generic.c:388 __proc_create+0xbc/0x260
    name len 0

or to a crash (the latter is more likely with CONFIG_DEBUG_SLAB=y, due
to the poisoning of freed memory).

Instead of zeroeing the pointer at multiple places, preinitialize
port->irqstr[j] to zero to fix this.

Fixes: 8b0bbd956228ae87 ("serial: sh-sci: Add support for R7S9210")
Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
 drivers/tty/serial/sh-sci.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/serial/sh-sci.c b/drivers/tty/serial/sh-sci.c
index 5808edfe3f7be404..f8e53ac5c17dfb94 100644
--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c
@@ -1872,6 +1872,7 @@ static int sci_request_irq(struct sci_port *port)
 		}

 		desc = sci_irq_desc + i;
+		port->irqstr[j] = NULL;
 		if (SCIx_TEIDRI_IRQ_EXISTS(port)) {
 			/*
 			 * ERI and BRI are muxed, just register ERI and
-- 
2.17.1