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

Lorenzo Bianconi
2023-03-08T09:10:05Z

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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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