linux-kernel - Re: [PATCH] iwlwifi: properly check debugfs dentry before using it

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Date:   Wed, 17 Apr 2019 10:02:54 +0300
From:   Luca Coelho <luca@...lho.fi>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Laura Abbott <labbott@...hat.com>, linux-kernel@...r.kernel.org,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        Intel Linux Wireless <linuxwifi@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        linux-wireless@...r.kernel.org, stable <stable@...r.kernel.org>
Subject: Re: [PATCH] iwlwifi: properly check debugfs dentry before using it

On Sat, 2019-03-30 at 10:31 +0100, Greg Kroah-Hartman wrote:
> debugfs can now report an error code if something went wrong instead
> of
> just NULL.  So if the return value is to be used as a "real" dentry,
> it
> needs to be checked if it is an error before dereferencing it.
> 
> This is now happening because of ff9fb72bc077 ("debugfs: return error
> values, not NULL").  If multiple iwlwifi devices are in the system,
> this
> can cause problems when the driver attempts to create the main
> debugfs
> directory again.  Later on in the code we fail horribly by trying to
> dereference a pointer that is an error value.
> 
> Reported-by: Laura Abbott <labbott@...hat.com>
> Cc: Johannes Berg <johannes.berg@...el.com>
> Cc: Emmanuel Grumbach <emmanuel.grumbach@...el.com>
> Cc: Luca Coelho <luciano.coelho@...el.com>
> Cc: Intel Linux Wireless <linuxwifi@...el.com>
> Cc: Kalle Valo <kvalo@...eaurora.org>
> Cc: stable <stable@...r.kernel.org> # 5.0
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> 
> 
> diff --git a/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> b/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> index 2453ceabf00d..6925527d8457 100644
> --- a/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> +++ b/drivers/net/wireless/intel/iwlwifi/mvm/debugfs-vif.c
> @@ -774,8 +774,7 @@ void iwl_mvm_vif_dbgfs_register(struct iwl_mvm
> *mvm, struct ieee80211_vif *vif)
>  		return;
>  
>  	mvmvif->dbgfs_dir = debugfs_create_dir("iwlmvm", dbgfs_dir);
> -
> -	if (!mvmvif->dbgfs_dir) {
> +	if (IS_ERR_OR_NULL(mvmvif->dbgfs_dir)) {
>  		IWL_ERR(mvm, "Failed to create debugfs directory under
> %pd\n",
>  			dbgfs_dir);
>  		return;

Thanks! I've applied this internally and will send upstream for v5.1-
rc* following our normal upstreaming process.

I added the other Reported-by that Laura asked for and added "mvm:" to
the subject.

--
Cheers,
Luca.