linux-kernel - [PATCH] Input: synaptics-rmi4 - Really fix attn

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Date:   Mon, 27 Apr 2020 14:55:48 -0700
From:   Evan Green <evgreen@...omium.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Evan Green <evgreen@...omium.org>, stable@...r.kernel.org,
        Nick Desaulniers <nick.desaulniers@...il.com>,
        Allison Randal <allison@...utok.net>,
        Andrew Duggan <aduggan@...aptics.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Enrico Weigelt <info@...ux.net>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] Input: synaptics-rmi4 - Really fix attn_data use-after-free

Fix a use-after-free noticed by running with KASAN enabled. If
rmi_irq_fn() is run twice in a row, then rmi_f11_attention() (among
others) will end up reading from drvdata->attn_data.data, which was
freed and left dangling in rmi_irq_fn().

Commit 55edde9fff1a ("Input: synaptics-rmi4 - prevent UAF reported by
KASAN") correctly identified and analyzed this bug. However the attempted
fix only NULLed out a local variable, missing the fact that
drvdata->attn_data is a struct, not a pointer.

NULL out the correct pointer in the driver data to prevent the attention
functions from copying from it.

Fixes: 55edde9fff1a ("Input: synaptics-rmi4 - prevent UAF reported by KASAN")
Fixes: b908d3cd812a ("Input: synaptics-rmi4 - allow to add attention data")

Signed-off-by: Evan Green <evgreen@...omium.org>

Cc: stable@...r.kernel.org
Cc: Nick Desaulniers <nick.desaulniers@...il.com>
---

 drivers/input/rmi4/rmi_driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/input/rmi4/rmi_driver.c b/drivers/input/rmi4/rmi_driver.c
index 190b9974526bb..c18e1a25bca6e 100644
--- a/drivers/input/rmi4/rmi_driver.c
+++ b/drivers/input/rmi4/rmi_driver.c
@@ -205,7 +205,7 @@ static irqreturn_t rmi_irq_fn(int irq, void *dev_id)
 
 	if (count) {
 		kfree(attn_data.data);
-		attn_data.data = NULL;
+		drvdata->attn_data.data = NULL;
 	}
 
 	if (!kfifo_is_empty(&drvdata->attn_fifo))
-- 
2.24.1