[PATCH 3.16 258/306] xc2028: Fix use-after-free bug properly

Ben Hutchings
2017-02-15T23:12:27Z

From: Takashi Iwai <tiwai@suse.de>

commit 22a1e7783e173ab3d86018eb590107d68df46c11 upstream.

The commit 8dfbcc4351a0 ("[media] xc2028: avoid use after free") tried
to address the reported use-after-free by clearing the reference.

However, it's clearing the wrong pointer; it sets NULL to
priv->ctrl.fname, but it's anyway overwritten by the next line
memcpy(&priv->ctrl, p, sizeof(priv->ctrl)).

OTOH, the actual code accessing the freed string is the strcmp() call
with priv->fname:
if (!firmware_name[0] && p->fname &&
priv->fname && strcmp(p->fname, priv->fname))
free_firmware(priv);

where priv->fname points to the previous file name, and this was
already freed by kfree().

For fixing the bug properly, this patch does the following:

- Keep the copy of firmware file name in only priv->fname,
priv->ctrl.fname isn't changed;
- The allocation is done only when the firmware gets loaded;
- The kfree() is called in free_firmware() commonly

Fixes: commit 8dfbcc4351a0 ('[media] xc2028: avoid use after free')
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
drivers/media/tuners/tuner-xc2028.c | 37 ++++++++++++++++---------------------
1 file changed, 16 insertions(+), 21 deletions(-)

--- a/drivers/media/tuners/tuner-xc2028.c
+++ b/drivers/media/tuners/tuner-xc2028.c
@@ -281,6 +281,14 @@ static void free_firmware(struct xc2028_
int i;
tuner_dbg("%s called\n", __func__);

+ /* free allocated f/w string */
+ if (priv->fname != firmware_name)
+ kfree(priv->fname);
+ priv->fname = NULL;
+
+ priv->state = XC2028_NO_FIRMWARE;
+ memset(&priv->cur_fw, 0, sizeof(priv->cur_fw));
+
if (!priv->firm)
return;

@@ -291,9 +299,6 @@ static void free_firmware(struct xc2028_

priv->firm = NULL;
priv->firm_size = 0;
- priv->state = XC2028_NO_FIRMWARE;
-
- memset(&priv->cur_fw, 0, sizeof(priv->cur_fw));
}

static int load_all_firmwares(struct dvb_frontend *fe,
@@ -884,9 +889,8 @@ read_not_reliable:
return 0;

fail:
- priv->state = XC2028_NO_FIRMWARE;
+ free_firmware(priv);

- memset(&priv->cur_fw, 0, sizeof(priv->cur_fw));
if (retry_count < 8) {
msleep(50);
retry_count++;
@@ -1332,11 +1336,8 @@ static int xc2028_dvb_release(struct dvb
mutex_lock(&xc2028_list_mutex);

/* only perform final cleanup if this is the last instance */
- if (hybrid_tuner_report_instance_count(priv) == 1) {
+ if (hybrid_tuner_report_instance_count(priv) == 1)
free_firmware(priv);
- kfree(priv->ctrl.fname);
- priv->ctrl.fname = NULL;
- }

if (priv)
hybrid_tuner_release_state(priv);
@@ -1399,19 +1400,8 @@ static int xc2028_set_config(struct dvb_

/*
* Copy the config data.
- * For the firmware name, keep a local copy of the string,
- * in order to avoid troubles during device release.
*/
- kfree(priv->ctrl.fname);
- priv->ctrl.fname = NULL;
memcpy(&priv->ctrl, p, sizeof(priv->ctrl));
- if (p->fname) {
- priv->ctrl.fname = kstrdup(p->fname, GFP_KERNEL);
- if (priv->ctrl.fname == NULL) {
- rc = -ENOMEM;
- goto unlock;
- }
- }

/*
* If firmware name changed, frees firmware. As free_firmware will
@@ -1426,10 +1416,15 @@ static int xc2028_set_config(struct dvb_

if (priv->state == XC2028_NO_FIRMWARE) {
if (!firmware_name[0])
- priv->fname = priv->ctrl.fname;
+ priv->fname = kstrdup(p->fname, GFP_KERNEL);
else
priv->fname = firmware_name;

+ if (!priv->fname) {
+ rc = -ENOMEM;
+ goto unlock;
+ }
+
rc = request_firmware_nowait(THIS_MODULE, 1,
priv->fname,
priv->i2c_props.adap->dev.parent,