lkml.org 
[lkml]   [2022]   [May]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH net] NFC: hci: fix sleep in atomic context bugs in nfc_hci_hcp_message_tx
Hello,

On Mon, 16 May 2022 08:44:39 +0200 Krzysztof wrote:

> > There are sleep in atomic context bugs when the request to secure
> > element of st21nfca is timeout. The root cause is that kzalloc and
> > alloc_skb with GFP_KERNEL parameter is called in st21nfca_se_wt_timeout
> > which is a timer handler. The call tree shows the execution paths that
> > could lead to bugs:
> >
> > (Interrupt context)
> > st21nfca_se_wt_timeout
> > nfc_hci_send_event
> > nfc_hci_hcp_message_tx
> > kzalloc(..., GFP_KERNEL) //may sleep
> > alloc_skb(..., GFP_KERNEL) //may sleep
> >
> > This patch changes allocation mode of kzalloc and alloc_skb from
> > GFP_KERNEL to GFP_ATOMIC in order to prevent atomic context from
> > sleeping. The GFP_ATOMIC flag makes memory allocation operation
> > could be used in atomic context.
> >
> > Fixes: 8b8d2e08bf0d ("NFC: HCI support")
> > Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
> > ---
> > net/nfc/hci/hcp.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/net/nfc/hci/hcp.c b/net/nfc/hci/hcp.c
> > index 05c60988f59..1caf9c2086f 100644
> > --- a/net/nfc/hci/hcp.c
> > +++ b/net/nfc/hci/hcp.c
> > @@ -30,7 +30,7 @@ int nfc_hci_hcp_message_tx(struct nfc_hci_dev *hdev, u8 pipe,
> > int hci_len, err;
> > bool firstfrag = true;
> >
> > - cmd = kzalloc(sizeof(struct hci_msg), GFP_KERNEL);
> > + cmd = kzalloc(sizeof(*cmd), GFP_ATOMIC);
>
> No, this does not look correct. This function can sleep, so it can use
> GFP_KERNEL. Please just look at the function before replacing any flags...

I am sorry, I don`t understand why nfc_hci_hcp_message_tx() can sleep.

I think st21nfca_se_wt_timeout() is a timer handler, which is in interrupt context.
The call tree shows the execution paths that could lead to bugs:

st21nfca_hci_se_io()
mod_timer(&info->se_info.bwi_timer,...)
st21nfca_se_wt_timeout() //timer handler, interrupt context
nfc_hci_send_event()
nfc_hci_hcp_message_tx()
kzalloc(..., GFP_KERNEL) //may sleep
alloc_skb(..., GFP_KERNEL) //may sleep

What`s more, I think the "mutex_lock(&hdev->msg_tx_mutex)" called by nfc_hci_hcp_message_tx()
is also improper.

Please correct me, If you think I am wrong. Thanks for your time.

Best regards,
Duoming Zhou

\
 
 \ /
  Last update: 2022-05-16 12:27    [W:0.068 / U:0.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site