linux-kernel - Re: [PATCH v10 3/7] i2c: fsi: Add port structures

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Date:   Wed, 20 Jun 2018 13:34:15 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Eddie James <eajames@...ux.vnet.ibm.com>, linux-i2c@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        wsa@...-dreams.de, robh+dt@...nel.org, joel@....id.au,
        mark.rutland@....com, gregkh@...uxfoundation.org,
        rdunlap@...radead.org, andy.shevchenko@...il.com, peda@...ntia.se
Subject: Re: [PATCH v10 3/7] i2c: fsi: Add port structures

On Wed, 2018-06-13 at 14:36 -0500, Eddie James wrote:
>  }
>  
> +static int fsi_i2c_remove(struct device *dev)
> +{
> +       struct fsi_i2c_master *i2c = dev_get_drvdata(dev);
> +       struct fsi_i2c_port *port;
> +
> +       list_for_each_entry(port, &i2c->ports, list) {
> +               i2c_del_adapter(&port->adapter);
> +               kfree(port);
> +       }
> +
> +       return 0;
> +}
> +

This is a use-after-free, the list linkage of the freed port is used to
get to the next one. With memory poisoning, kbooom !

You can fold that in:

>From f9d9092160897e7308f6990067a03e937339537f Mon Sep 17 00:00:00 2001
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
Date: Wed, 20 Jun 2018 13:27:32 +1000
Subject: [PATCH] i2c: fsi: Fix use after free

Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
---
 drivers/i2c/busses/i2c-fsi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-fsi.c b/drivers/i2c/busses/i2c-fsi.c
index 713959b44403..ff69ab6aa79a 100644
--- a/drivers/i2c/busses/i2c-fsi.c
+++ b/drivers/i2c/busses/i2c-fsi.c
@@ -696,9 +696,10 @@ static int fsi_i2c_probe(struct device *dev)
 static int fsi_i2c_remove(struct device *dev)
 {
 	struct fsi_i2c_master *i2c = dev_get_drvdata(dev);
-	struct fsi_i2c_port *port;
+	struct fsi_i2c_port *port, *tmp;
 
-	list_for_each_entry(port, &i2c->ports, list) {
+	list_for_each_entry_safe(port,tmp, &i2c->ports, list) {
+		list_del(&port->list);
 		i2c_del_adapter(&port->adapter);
 		kfree(port);
 	}