diff mbox series

[v2] usb: gadget: ncm: Fix handling of zero block length packets

Message ID 20240228115441.2105585-1-quic_kriskura@quicinc.com (mailing list archive)
State Accepted
Commit f90ce1e04cbcc76639d6cba0fdbd820cd80b3c70
Headers show
Series [v2] usb: gadget: ncm: Fix handling of zero block length packets | expand

Commit Message

Krishna Kurapati Feb. 28, 2024, 11:54 a.m. UTC
While connecting to a Linux host with CDC_NCM_NTB_DEF_SIZE_TX
set to 65536, it has been observed that we receive short packets,
which come at interval of 5-10 seconds sometimes and have block
length zero but still contain 1-2 valid datagrams present.

According to the NCM spec:

"If wBlockLength = 0x0000, the block is terminated by a
short packet. In this case, the USB transfer must still
be shorter than dwNtbInMaxSize or dwNtbOutMaxSize. If
exactly dwNtbInMaxSize or dwNtbOutMaxSize bytes are sent,
and the size is a multiple of wMaxPacketSize for the
given pipe, then no ZLP shall be sent.

wBlockLength= 0x0000 must be used with extreme care, because
of the possibility that the host and device may get out of
sync, and because of test issues.

wBlockLength = 0x0000 allows the sender to reduce latency by
starting to send a very large NTB, and then shortening it when
the sender discovers that there’s not sufficient data to justify
sending a large NTB"

However, there is a potential issue with the current implementation,
as it checks for the occurrence of multiple NTBs in a single
giveback by verifying if the leftover bytes to be processed is zero
or not. If the block length reads zero, we would process the same
NTB infintely because the leftover bytes is never zero and it leads
to a crash. Fix this by bailing out if block length reads zero.

Cc: <stable@vger.kernel.org>
Fixes: 427694cfaafa ("usb: gadget: ncm: Handle decoding of multiple NTB's in unwrap call")
Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
---
Changes in v2:
Removed goto label

Link to v1:
https://lore.kernel.org/all/20240226112815.2616719-1-quic_kriskura@quicinc.com/

 drivers/usb/gadget/function/f_ncm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Maciej Żenczykowski Feb. 28, 2024, 12:48 p.m. UTC | #1
On Wed, Feb 28, 2024 at 3:54 AM Krishna Kurapati
<quic_kriskura@quicinc.com> wrote:
>
> While connecting to a Linux host with CDC_NCM_NTB_DEF_SIZE_TX
> set to 65536, it has been observed that we receive short packets,
> which come at interval of 5-10 seconds sometimes and have block
> length zero but still contain 1-2 valid datagrams present.
>
> According to the NCM spec:
>
> "If wBlockLength = 0x0000, the block is terminated by a
> short packet. In this case, the USB transfer must still
> be shorter than dwNtbInMaxSize or dwNtbOutMaxSize. If
> exactly dwNtbInMaxSize or dwNtbOutMaxSize bytes are sent,
> and the size is a multiple of wMaxPacketSize for the
> given pipe, then no ZLP shall be sent.
>
> wBlockLength= 0x0000 must be used with extreme care, because
> of the possibility that the host and device may get out of
> sync, and because of test issues.
>
> wBlockLength = 0x0000 allows the sender to reduce latency by
> starting to send a very large NTB, and then shortening it when
> the sender discovers that there’s not sufficient data to justify
> sending a large NTB"
>
> However, there is a potential issue with the current implementation,
> as it checks for the occurrence of multiple NTBs in a single
> giveback by verifying if the leftover bytes to be processed is zero
> or not. If the block length reads zero, we would process the same
> NTB infintely because the leftover bytes is never zero and it leads
> to a crash. Fix this by bailing out if block length reads zero.
>
> Cc: <stable@vger.kernel.org>
> Fixes: 427694cfaafa ("usb: gadget: ncm: Handle decoding of multiple NTB's in unwrap call")
> Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>
> ---
> Changes in v2:
> Removed goto label
>
> Link to v1:
> https://lore.kernel.org/all/20240226112815.2616719-1-quic_kriskura@quicinc.com/
>
>  drivers/usb/gadget/function/f_ncm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
> index e2a059cfda2c..28f4e6552e84 100644
> --- a/drivers/usb/gadget/function/f_ncm.c
> +++ b/drivers/usb/gadget/function/f_ncm.c
> @@ -1346,7 +1346,7 @@ static int ncm_unwrap_ntb(struct gether *port,
>         if (to_process == 1 &&
>             (*(unsigned char *)(ntb_ptr + block_len) == 0x00)) {
>                 to_process--;
> -       } else if (to_process > 0) {
> +       } else if ((to_process > 0) && (block_len != 0)) {
>                 ntb_ptr = (unsigned char *)(ntb_ptr + block_len);
>                 goto parse_ntb;
>         }
> --
> 2.34.1

Reviewed-by: Maciej Żenczykowski <maze@google.com>
diff mbox series

Patch

diff --git a/drivers/usb/gadget/function/f_ncm.c b/drivers/usb/gadget/function/f_ncm.c
index e2a059cfda2c..28f4e6552e84 100644
--- a/drivers/usb/gadget/function/f_ncm.c
+++ b/drivers/usb/gadget/function/f_ncm.c
@@ -1346,7 +1346,7 @@  static int ncm_unwrap_ntb(struct gether *port,
 	if (to_process == 1 &&
 	    (*(unsigned char *)(ntb_ptr + block_len) == 0x00)) {
 		to_process--;
-	} else if (to_process > 0) {
+	} else if ((to_process > 0) && (block_len != 0)) {
 		ntb_ptr = (unsigned char *)(ntb_ptr + block_len);
 		goto parse_ntb;
 	}