[PATCH] Input: cyttsp4_core: fix use after free bug

[PATCH] Input: cyttsp4_core: fix use after free bug

[Pan Bian]

The device md->input is used after it is released. Setting the device
data to NULL is unnecessary as the device is never used again. Instead,
md->input should be assigned NULL to avoid accessing the freed memory
accidently. Besides, checking md->si against NULL is superfluous as it
points to a variable address, which cannot be NULL.

Signed-off-by: Pan Bian <bianpan2016@163.com>
---
 drivers/input/touchscreen/cyttsp4_core.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/input/touchscreen/cyttsp4_core.c b/drivers/input/touchscreen/cyttsp4_core.c
index 4b22d49a0f49..2cd5f835665e 100644
--- a/drivers/input/touchscreen/cyttsp4_core.c
+++ b/drivers/input/touchscreen/cyttsp4_core.c
@@ -1990,11 +1990,6 @@ static int cyttsp4_mt_probe(struct cyttsp4 *cd)
 
 	/* get sysinfo */
 	md->si = &cd->sysinfo;
-	if (!md->si) {
-		dev_err(dev, "%s: Fail get sysinfo pointer from core p=%p\n",
-			__func__, md->si);
-		goto error_get_sysinfo;
-	}
 
 	rc = cyttsp4_setup_input_device(cd);
 	if (rc)
@@ -2004,8 +1999,7 @@ static int cyttsp4_mt_probe(struct cyttsp4 *cd)
 
 error_init_input:
 	input_free_device(md->input);
-error_get_sysinfo:
-	input_set_drvdata(md->input, NULL);
+	md->input = NULL;
 error_alloc_failed:
 	dev_err(dev, "%s failed.\n", __func__);
 	return rc;
-- 
2.7.4

Re: [PATCH] Input: cyttsp4_core: fix use after free bug

[Dmitry Torokhov]

On Tue, Nov 05, 2019 at 02:46:19PM +0800, Pan Bian wrote:
> The device md->input is used after it is released. Setting the device
> data to NULL is unnecessary as the device is never used again. Instead,
> md->input should be assigned NULL to avoid accessing the freed memory
> accidently.

No, we are tearing up the device anyway, I'd leave it as it was, so I'll
drop this chunk and apply the rest.

Thank you.

-- 
Dmitry