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SubjectRe: [PATCH 1/2] media: ir-kbd-i2c: prevent potential NULL pointer access
On Mon, Jul 22, 2019 at 07:26:31PM +0200, Wolfram Sang wrote:
> i2c_new_dummy() can fail returning a NULL pointer. The code does not
> bail out in this case and the returned pointer is blindly used.

I don't see how. The existing code tries to set up the tx part; if
i2c_new_dummy() return NULL then the rcdev is registered without tx,
and tx_c is never used.

> Convert
> to devm_i2c_new_dummy_device() which returns an ERR_PTR and also bail
> out when failing the validity check.

Possibly I was being overly cautious with not bailing out if tx can't
be registered; moving to devm is probably a good idea. However the
commit message is misleading, because the existing code has no
NULL pointer access.

Sean

>
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
> ---
> drivers/media/i2c/ir-kbd-i2c.c | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/media/i2c/ir-kbd-i2c.c b/drivers/media/i2c/ir-kbd-i2c.c
> index 876d7587a1da..f46717052efc 100644
> --- a/drivers/media/i2c/ir-kbd-i2c.c
> +++ b/drivers/media/i2c/ir-kbd-i2c.c
> @@ -885,9 +885,12 @@ static int ir_probe(struct i2c_client *client, const struct i2c_device_id *id)
> INIT_DELAYED_WORK(&ir->work, ir_work);
>
> if (probe_tx) {
> - ir->tx_c = i2c_new_dummy(client->adapter, 0x70);
> - if (!ir->tx_c) {
> + ir->tx_c = devm_i2c_new_dummy_device(&client->dev,
> + client->adapter, 0x70);
> + if (IS_ERR(ir->tx_c)) {
> dev_err(&client->dev, "failed to setup tx i2c address");
> + err = PTR_ERR(ir->tx_c);
> + goto err_out_free;
> } else if (!zilog_init(ir)) {
> ir->carrier = 38000;
> ir->duty_cycle = 40;
> @@ -904,9 +907,6 @@ static int ir_probe(struct i2c_client *client, const struct i2c_device_id *id)
> return 0;
>
> err_out_free:
> - if (ir->tx_c)
> - i2c_unregister_device(ir->tx_c);
> -
> /* Only frees rc if it were allocated internally */
> rc_free_device(rc);
> return err;
> @@ -919,9 +919,6 @@ static int ir_remove(struct i2c_client *client)
> /* kill outstanding polls */
> cancel_delayed_work_sync(&ir->work);
>
> - if (ir->tx_c)
> - i2c_unregister_device(ir->tx_c);
> -
> /* unregister device */
> rc_unregister_device(ir->rc);
>
> --
> 2.20.1

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