[PATCH] [media] Staging: media/lirc: don't call put_ir_rx on rx twice

[PATCH] [media] Staging: media/lirc: don't call put_ir_rx on rx twice

[Colin King]

From: Colin Ian King <colin.king@canonical.com>

There is an exit path where rx is kfree'd on put_ir_rx and then
a jump to label out_put_xx will again kfree it with another
call to put_ir_rx.  Fix this by adding a new label that avoids
this 2nd call to put_ir_rx for this specific case.

Detected with CoverityScan, CID#145119 ("Use after free")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/staging/media/lirc/lirc_zilog.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/media/lirc/lirc_zilog.c b/drivers/staging/media/lirc/lirc_zilog.c
index 34aac3e..5dd1e62 100644
--- a/drivers/staging/media/lirc/lirc_zilog.c
+++ b/drivers/staging/media/lirc/lirc_zilog.c
@@ -1597,7 +1597,7 @@ static int ir_probe(struct i2c_client *client, const struct i2c_device_id *id)
 			i2c_set_clientdata(client, NULL);
 			put_ir_rx(rx, true);
 			ir->l.features &= ~LIRC_CAN_REC_LIRCCODE;
-			goto out_put_xx;
+			goto out_put_tx;
 		}
 
 		/* Proceed only if the Tx client is also ready */
@@ -1637,6 +1637,7 @@ static int ir_probe(struct i2c_client *client, const struct i2c_device_id *id)
 out_put_xx:
 	if (rx != NULL)
 		put_ir_rx(rx, true);
+out_put_tx:
 	if (tx != NULL)
 		put_ir_tx(tx, true);
 out_put_ir:
-- 
2.10.2

Re: [PATCH] [media] Staging: media/lirc: don't call put_ir_rx on rx twice

[Dan Carpenter]

This one is a false positive.  The original code is correct.

I was looking through my mail boxes to see the history of this and why
it hadn't been fixed earlier.  Someone tried to fix it in 2011:
https://www.spinics.net/lists/linux-driver-devel/msg17403.html
Then I complained about it again in 2014 when I was looking at a
different bug in that same function.  Now you're the third person to
think this code is suspicious.

I think part of the problem is that get_ir_rx(ir) is hidden as a
function parameter instead of on its own line.  But really even that
wouldn't totally fix the issue.

regards,
dan carpenter