Re: [PATCH] wireless: mt76: mt7921: Fix use-after-free in fw features query.

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> From: Ben Greear <greearb@candelatech.com>
> 
> Stop referencing 'features' memory after release_firmware is called.
> 
> Fixes this crash:
> 
> RIP: 0010:mt7921_check_offload_capability+0x17d
> mt7921_pci_probe+0xca/0x4b0

Hi Ben,

thx for fixing it. Just few minor comments inline.

Regards,
Lorenzo

> ...
> 
> Signed-off-by: Ben Greear <greearb@candelatech.com>
> ---
>  drivers/net/wireless/mediatek/mt76/mt7921/init.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/wireless/mediatek/mt76/mt7921/init.c b/drivers/net/wireless/mediatek/mt76/mt7921/init.c
> index 38d6563cb12f..3b6fb1a6b351 100644
> --- a/drivers/net/wireless/mediatek/mt76/mt7921/init.c
> +++ b/drivers/net/wireless/mediatek/mt76/mt7921/init.c
> @@ -171,6 +171,7 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
>  	const struct firmware *fw;
>  	int ret, i, offset = 0;
>  	const u8 *data, *end;
> +	u8 rv = 0;

I would say we can use a more meaningful name here, something like offload_capa
or similar. Moreover I thin you can move features pointer just in the
if (rel_info->tag == MT7921_FW_TAG_FEATURE) block.

Regards,
Lorenzo

>  
>  	ret = request_firmware(&fw, fw_wm, dev);
>  	if (ret)
> @@ -197,12 +198,17 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
>  	data += sizeof(*rel_info);
>  	end = data + le16_to_cpu(rel_info->len);
>  
> +	/* TODO:  This needs better sanity checking I think.
> +	 * Likely a corrupted firmware with bad rel_info->len, for instance,
> +	 * would blow this up.
> +	 */
>  	while (data < end) {
>  		rel_info = (struct mt7921_realease_info *)data;
>  		data += sizeof(*rel_info);
>  
>  		if (rel_info->tag == MT7921_FW_TAG_FEATURE) {
>  			features = (struct mt7921_fw_features *)data;
> +			rv = features->data;
>  			break;
>  		}
>  
> @@ -211,7 +217,7 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
>  
>  	release_firmware(fw);
>  
> -	return features ? features->data : 0;
> +	return rv;
>  }
>  EXPORT_SYMBOL_GPL(mt7921_check_offload_capability);
>  
> -- 
> 2.39.1
> 

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