Re: [PATCH] nfc: st21nfca: fix possible double free in st21nfca_im_recv_dep_res_cb()

[Hangyu Hua]

On 2022/6/23 17:42, Paolo Abeni wrote:
> On Wed, 2022-06-22 at 14:51 +0800, Hangyu Hua wrote:
> > nfc_tm_data_received will free skb internally when it fails. There is no
> > need to free skb in st21nfca_im_recv_dep_res_cb again.
> >
> > Fix this by setting skb to NULL when nfc_tm_data_received fails.
> >
> > Fixes: 1892bf844ea0 ("NFC: st21nfca: Adding P2P support to st21nfca in Initiator & Target mode")
> > Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx>
> > ---
> >   drivers/nfc/st21nfca/dep.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/nfc/st21nfca/dep.c b/drivers/nfc/st21nfca/dep.c
> > index 1ec651e31064..07ac5688011c 100644
> > --- a/drivers/nfc/st21nfca/dep.c
> > +++ b/drivers/nfc/st21nfca/dep.c
> > @@ -594,7 +594,8 @@ static void st21nfca_im_recv_dep_res_cb(void *context, struct sk_buff *skb,
> >   			    ST21NFCA_NFC_DEP_PFB_PNI(dep_res->pfb + 1);
> >   			size++;
> >   			skb_pull(skb, size);
> > -			nfc_tm_data_received(info->hdev->ndev, skb);
> > +			if (nfc_tm_data_received(info->hdev->ndev, skb))
> > +				skb = NULL;
>
> Note that 'skb' not used (nor freed) by this function after this point:
> the next 'break' statement refears to the inner switch, and land to the
> execution flow to the 'return' statement a few lines below.
> kfree_skb(skb) is never reached.
>
> Paolo

My fault. I messed up two switch statements. I will be more careful next 
time.

hangyu