Re: [PATCH] ipmi: ssif: initialize ssif_info->client early

[Corey Minyard]

On Wed, Dec 08, 2021 at 10:32:39AM +0100, Mian Yousaf Kaukab wrote:
> During probe ssif_info->client is dereferenced in error path. However,
> it is set when some of the error checking has already been done. This
> causes following kernel crash if an error path is taken:
> 
> [   30.645593][  T674] ipmi_ssif 0-000e: ipmi_ssif: Not probing, Interface already present
> [   30.657616][  T674] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000088
> ...
> [   30.657723][  T674] pc : __dev_printk+0x28/0xa0
> [   30.657732][  T674] lr : _dev_err+0x7c/0xa0
> ...
> [   30.657772][  T674] Call trace:
> [   30.657775][  T674]  __dev_printk+0x28/0xa0
> [   30.657778][  T674]  _dev_err+0x7c/0xa0
> [   30.657781][  T674]  ssif_probe+0x548/0x900 [ipmi_ssif 62ce4b08badc1458fd896206d9ef69a3c31f3d3e]
> [   30.657791][  T674]  i2c_device_probe+0x37c/0x3c0
> ...
> 
> Initialize ssif_info->client before any error path can be taken. Clear
> i2c_client data in the error path to prevent the dangling pointer from
> leaking.

Sigh, I just sent some fixes up to Linus, so this was bound to happen :).
This is in my for-next tree, I'll send it up in a few days if everything
is ok.

Thanks,

-corey

> 
> Fixes: c4436c9149c5 ("ipmi_ssif: avoid registering duplicate ssif interface")
> Suggested-by: Takashi Iwai <tiwai@xxxxxxx>
> Signed-off-by: Mian Yousaf Kaukab <ykaukab@xxxxxxx>
> ---
>  drivers/char/ipmi/ipmi_ssif.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
> index 0c62e578749e..48aab77abebf 100644
> --- a/drivers/char/ipmi/ipmi_ssif.c
> +++ b/drivers/char/ipmi/ipmi_ssif.c
> @@ -1659,6 +1659,9 @@ static int ssif_probe(struct i2c_client *client, const struct i2c_device_id *id)
>  		}
>  	}
>  
> +	ssif_info->client = client;
> +	i2c_set_clientdata(client, ssif_info);
> +
>  	rv = ssif_check_and_remove(client, ssif_info);
>  	/* If rv is 0 and addr source is not SI_ACPI, continue probing */
>  	if (!rv && ssif_info->addr_source == SI_ACPI) {
> @@ -1679,9 +1682,6 @@ static int ssif_probe(struct i2c_client *client, const struct i2c_device_id *id)
>  		ipmi_addr_src_to_str(ssif_info->addr_source),
>  		client->addr, client->adapter->name, slave_addr);
>  
> -	ssif_info->client = client;
> -	i2c_set_clientdata(client, ssif_info);
> -
>  	/* Now check for system interface capabilities */
>  	msg[0] = IPMI_NETFN_APP_REQUEST << 2;
>  	msg[1] = IPMI_GET_SYSTEM_INTERFACE_CAPABILITIES_CMD;
> @@ -1881,6 +1881,7 @@ static int ssif_probe(struct i2c_client *client, const struct i2c_device_id *id)
>  
>  		dev_err(&ssif_info->client->dev,
>  			"Unable to start IPMI SSIF: %d\n", rv);
> +		i2c_set_clientdata(client, NULL);
>  		kfree(ssif_info);
>  	}
>  	kfree(resp);
> -- 
> 2.31.1
>