Re: [PATCH] nfc: fix memory leak of se_io context in nfc_genl_se_io

[Fedor Pchelkin <pchelkin@ispras.ru>]

On Tue, Feb 28, 2023 at 11:14:03AM +0100, Krzysztof Kozlowski wrote:
> On 27/02/2023 16:05, Fedor Pchelkin wrote:
> >>> Fixes: 5ce3f32b5264 ("NFC: netlink: SE API implementation")
> >>> Reported-by: syzbot+df64c0a2e8d68e78a4fa@syzkaller.appspotmail.com
> >>> Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
> >>> Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
> >>
> >> SoB order is a bit odd. Who is the author?
> >>
> > 
> > The author is me (Fedor). I thought the authorship is expressed with the
> > first Signed-off-by line, isn't it?
> 
> Yes and since you are sending it, then what is Alexey's Sob for? The
> tags are in order...
> 

Now I get what you mean. Alexey is my supervisor and the patches I make
are passed through him (even though they are sent by me). If this is not
a customary thing, then I'll take that into account for further
submissions. I guess something like Acked-by is more appropriate?

> > 
> >>> ---
> >>>  drivers/nfc/st-nci/se.c   | 6 ++++++
> >>>  drivers/nfc/st21nfca/se.c | 6 ++++++
> >>>  net/nfc/netlink.c         | 4 ++++
> >>>  3 files changed, 16 insertions(+)
> >>>
> >>> diff --git a/drivers/nfc/st-nci/se.c b/drivers/nfc/st-nci/se.c
> >>> index ec87dd21e054..b2f1ced8e6dd 100644
> >>> --- a/drivers/nfc/st-nci/se.c
> >>> +++ b/drivers/nfc/st-nci/se.c
> >>> @@ -672,6 +672,12 @@ int st_nci_se_io(struct nci_dev *ndev, u32 se_idx,
> >>>  					ST_NCI_EVT_TRANSMIT_DATA, apdu,
> >>>  					apdu_length)
> >> nci_hci_send_event() should also free it in its error paths.
> >> nci_data_exchange_complete() as well? Who eventually frees it? These
> >> might be separate patches.
> >>
> >>
> > 
> > nci_hci_send_event(), as I can see, should not free the callback context.
> > I should have probably better explained that in the commit info (will
> > include this in the patch v2), but the main thing is: nfc_se_io() is
> > called with se_io_cb callback function as an argument and that callback is 
> > the exact place where an allocated se_io_ctx context should be freed. And
> > it is actually freed there unless some error path happens that leads the
> 
> Exactly, so why nci_hci_send_event() error path should not free it?
> 

nci_hci_send_event() should not free it on its error path because the
bwi_timer is already charged before nci_hci_send_event() is called.

The pattern in the .se_io functions of the corresponding drivers (st-nci,
st21nfca) is following:

	info->se_info.cb = cb;
	info->se_info.cb_context = cb_context;
	mod_timer(&info->se_info.bwi_timer, jiffies +
		  msecs_to_jiffies(info->se_info.wt_timeout)); // <-charged
	info->se_info.bwi_active = true;
	return nci_hci_send_event(...);

As the timer is charged, it will eventually call se_io_cb() to free the
context, even if the error path is taken inside nci_hci_send_event().

Am I missing something?

> > timer which triggers this se_io_cb callback not to be charged at all.
> > 
> 
> 
> Best regards,
> Krzysztof
>