Re: [PATCH v3] wifi: mt76: mt792x: fix use-after-free in mt76_rx_poll_complete

["Eason Lai (賴易聖)" <Eason.Lai@mediatek.com>]

On Mon, 2026-06-15 at 02:17 +0000, Eason Lai (賴易聖) wrote:
> After looking into the mac80211 STA removal flow, I didn't notice
> that synchronize_net() is invoked after mt76_sta_pre_rcu_remove().
> You are right. I will check mt7925_change_vif_links(). Thanks for the
> suggestion.
> 
> Best regards,
> Eason
> 
> -----Original Message-----
> From: Felix Fietkau <nbd@nbd.name> 
> Sent: Monday, June 1, 2026 7:13 PM
> To: JB Tsai (蔡志彬) <Jb.Tsai@mediatek.com>; lorenzo@kernel.org
> Cc: linux-wireless@vger.kernel.org;
> linux-mediatek@lists.infradead.org; Deren Wu (武德仁)
> <Deren.Wu@mediatek.com>; Sean Wang <Sean.Wang@mediatek.com>; Quan
> Zhou (周全) <Quan.Zhou@mediatek.com>; Ryder Lee
> <Ryder.Lee@mediatek.com>; Leon Yen (顏良儒) <Leon.Yen@mediatek.com>;
> Litien Chang (張立典) <Litien.Chang@mediatek.com>; Eason Lai (賴易聖)
> <Eason.Lai@mediatek.com>
> Subject: Re: [PATCH v3] wifi: mt76: mt792x: fix use-after-free in
> mt76_rx_poll_complete
> 
> On 06.05.26 10:43, JB Tsai wrote:
> > From: Eason Lai <Eason.Lai@mediatek.com>
> > 
> > A use-after-free issue occurs in mt76_rx_poll_complete due to a
> > race 
> > condition. The STA has already been removed, but the rx_status
> > still 
> > had a pointer to the wcid in the STA.
> > 
> > Use wcid_idx instead of storing the wcid pointer, and look up the
> > wcid 
> > via rcu_dereference() by wcid_idx.
> Unless I'm misreading something, it seems to me that this patch
> papers over a different bug instead of fixing the root cause.
> Right now the rx processing code relies on RCU to protect the wcid
> and sta data structures.
> The rcu lock/unlock around polling also seems correct to me.
> 
> Are the freed wcid pointers maybe related to a vif sta instead of an
> actual station? The use of devm_kfree in mt7925_change_vif_links
> looks suspicious to me.
> 
> Please let me know if I'm missing something here.
> 
> - Felix

The new patch is posted here:
https://lore.kernel.org/all/20260701010654.956863-1-eason.lai@mediatek.com/

Best regards,
Eason