* [PATCH v2 1/2] HID: u2fzero: explicitly check for errors
@ 2021-10-18 12:21 Andrej Shadura
2021-10-18 12:21 ` [PATCH v2 2/2] HID: u2fzero: properly handle timeouts in usb_submit_urb Andrej Shadura
2021-10-18 14:15 ` [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Alan Stern
0 siblings, 2 replies; 5+ messages in thread
From: Andrej Shadura @ 2021-10-18 12:21 UTC (permalink / raw)
To: Jiří Kosina; +Cc: linux-input, linux-usb, stable, kernel
The previous commit fixed handling of incomplete packets but broke error
handling: offsetof returns an unsigned value (size_t), but when compared
against the signed return value, the return value is interpreted as if
it were unsigned, so negative return values are never less than the
offset.
Fixes: 22d65765f211 ("HID: u2fzero: ignore incomplete packets without data")
Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
---
drivers/hid/hid-u2fzero.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
index d70cd3d7f583..5145d758bea0 100644
--- a/drivers/hid/hid-u2fzero.c
+++ b/drivers/hid/hid-u2fzero.c
@@ -200,7 +200,7 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
ret = u2fzero_recv(dev, &req, &resp);
/* ignore errors or packets without data */
- if (ret < offsetof(struct u2f_hid_msg, init.data))
+ if (ret < 0 || ret < offsetof(struct u2f_hid_msg, init.data))
return 0;
/* only take the minimum amount of data it is safe to take */
--
2.33.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v2 2/2] HID: u2fzero: properly handle timeouts in usb_submit_urb
2021-10-18 12:21 [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Andrej Shadura
@ 2021-10-18 12:21 ` Andrej Shadura
2021-10-18 14:15 ` [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Alan Stern
1 sibling, 0 replies; 5+ messages in thread
From: Andrej Shadura @ 2021-10-18 12:21 UTC (permalink / raw)
To: Jiří Kosina; +Cc: linux-input, linux-usb, stable, kernel
The wait_for_completion_timeout function returns 0 if timed out or a
positive value if completed. Hence, "less than zero" comparison always
misses timeouts and doesn't kill the URB as it should, leading to
re-sending it while it is active.
Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
---
drivers/hid/hid-u2fzero.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
index 5145d758bea0..562da98cfb82 100644
--- a/drivers/hid/hid-u2fzero.c
+++ b/drivers/hid/hid-u2fzero.c
@@ -132,7 +132,7 @@ static int u2fzero_recv(struct u2fzero_device *dev,
ret = (wait_for_completion_timeout(
&ctx.done, msecs_to_jiffies(USB_CTRL_SET_TIMEOUT)));
- if (ret < 0) {
+ if (ret == 0) {
usb_kill_urb(dev->urb);
hid_err(hdev, "urb submission timed out");
} else {
--
2.33.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/2] HID: u2fzero: explicitly check for errors
2021-10-18 12:21 [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Andrej Shadura
2021-10-18 12:21 ` [PATCH v2 2/2] HID: u2fzero: properly handle timeouts in usb_submit_urb Andrej Shadura
@ 2021-10-18 14:15 ` Alan Stern
2021-10-18 14:17 ` Andrej Shadura
1 sibling, 1 reply; 5+ messages in thread
From: Alan Stern @ 2021-10-18 14:15 UTC (permalink / raw)
To: Andrej Shadura
Cc: Jiří Kosina, linux-input, linux-usb, stable, kernel
On Mon, Oct 18, 2021 at 02:21:43PM +0200, Andrej Shadura wrote:
> The previous commit fixed handling of incomplete packets but broke error
> handling: offsetof returns an unsigned value (size_t), but when compared
> against the signed return value, the return value is interpreted as if
> it were unsigned, so negative return values are never less than the
> offset.
>
> Fixes: 22d65765f211 ("HID: u2fzero: ignore incomplete packets without data")
> Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
> Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
> ---
> drivers/hid/hid-u2fzero.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
> index d70cd3d7f583..5145d758bea0 100644
> --- a/drivers/hid/hid-u2fzero.c
> +++ b/drivers/hid/hid-u2fzero.c
> @@ -200,7 +200,7 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
> ret = u2fzero_recv(dev, &req, &resp);
>
> /* ignore errors or packets without data */
> - if (ret < offsetof(struct u2f_hid_msg, init.data))
> + if (ret < 0 || ret < offsetof(struct u2f_hid_msg, init.data))
Although the patch description does a good job of explaining what's
happening, someone merely reading the code will most likely not
understand.
One alternative is to add a comment. Another is simply to force a
signed integer comparison:
if (ret < (ssize_t) offsetof(...
Alan Stern
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/2] HID: u2fzero: explicitly check for errors
2021-10-18 14:15 ` [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Alan Stern
@ 2021-10-18 14:17 ` Andrej Shadura
2021-10-18 14:38 ` Alan Stern
0 siblings, 1 reply; 5+ messages in thread
From: Andrej Shadura @ 2021-10-18 14:17 UTC (permalink / raw)
To: Alan Stern; +Cc: Jiří Kosina, linux-input, linux-usb, stable, kernel
On 18/10/2021 16:15, Alan Stern wrote:
> On Mon, Oct 18, 2021 at 02:21:43PM +0200, Andrej Shadura wrote:
>> The previous commit fixed handling of incomplete packets but broke error
>> handling: offsetof returns an unsigned value (size_t), but when compared
>> against the signed return value, the return value is interpreted as if
>> it were unsigned, so negative return values are never less than the
>> offset.
>>
>> Fixes: 22d65765f211 ("HID: u2fzero: ignore incomplete packets without data")
>> Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
>> Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
>> ---
>> drivers/hid/hid-u2fzero.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
>> index d70cd3d7f583..5145d758bea0 100644
>> --- a/drivers/hid/hid-u2fzero.c
>> +++ b/drivers/hid/hid-u2fzero.c
>> @@ -200,7 +200,7 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
>> ret = u2fzero_recv(dev, &req, &resp);
>>
>> /* ignore errors or packets without data */
>> - if (ret < offsetof(struct u2f_hid_msg, init.data))
>> + if (ret < 0 || ret < offsetof(struct u2f_hid_msg, init.data))
>
> Although the patch description does a good job of explaining what's
> happening, someone merely reading the code will most likely not
> understand.
>
> One alternative is to add a comment. Another is simply to force a
> signed integer comparison:
>
> if (ret < (ssize_t) offsetof(...
I have considered that, but I thought that is actually less readable
than having two conditions. I’m curious that you say "ignore errors or
packets without data" is not clear enough — how would you reword that
without inflating it too much?
--
Cheers,
Andrej
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2 1/2] HID: u2fzero: explicitly check for errors
2021-10-18 14:17 ` Andrej Shadura
@ 2021-10-18 14:38 ` Alan Stern
0 siblings, 0 replies; 5+ messages in thread
From: Alan Stern @ 2021-10-18 14:38 UTC (permalink / raw)
To: Andrej Shadura
Cc: Jiří Kosina, linux-input, linux-usb, stable, kernel
On Mon, Oct 18, 2021 at 04:17:57PM +0200, Andrej Shadura wrote:
> On 18/10/2021 16:15, Alan Stern wrote:
> > On Mon, Oct 18, 2021 at 02:21:43PM +0200, Andrej Shadura wrote:
> > > The previous commit fixed handling of incomplete packets but broke error
> > > handling: offsetof returns an unsigned value (size_t), but when compared
> > > against the signed return value, the return value is interpreted as if
> > > it were unsigned, so negative return values are never less than the
> > > offset.
> > >
> > > Fixes: 22d65765f211 ("HID: u2fzero: ignore incomplete packets without data")
> > > Fixes: 42337b9d4d95 ("HID: add driver for U2F Zero built-in LED and RNG")
> > > Signed-off-by: Andrej Shadura <andrew.shadura@collabora.co.uk>
> > > ---
> > > drivers/hid/hid-u2fzero.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/hid/hid-u2fzero.c b/drivers/hid/hid-u2fzero.c
> > > index d70cd3d7f583..5145d758bea0 100644
> > > --- a/drivers/hid/hid-u2fzero.c
> > > +++ b/drivers/hid/hid-u2fzero.c
> > > @@ -200,7 +200,7 @@ static int u2fzero_rng_read(struct hwrng *rng, void *data,
> > > ret = u2fzero_recv(dev, &req, &resp);
> > > /* ignore errors or packets without data */
> > > - if (ret < offsetof(struct u2f_hid_msg, init.data))
> > > + if (ret < 0 || ret < offsetof(struct u2f_hid_msg, init.data))
> >
> > Although the patch description does a good job of explaining what's
> > happening, someone merely reading the code will most likely not
> > understand.
> >
> > One alternative is to add a comment. Another is simply to force a
> > signed integer comparison:
> >
> > if (ret < (ssize_t) offsetof(...
>
> I have considered that, but I thought that is actually less readable than
> having two conditions. I’m curious that you say "ignore errors or packets
> without data" is not clear enough — how would you reword that without
> inflating it too much?
You misunderstand. The existing comment is clear enough. But the code
itself is misleading:
if (ret < 0 || ret < offsetof(...
looks redundant. Someone reading it for the first time will
automatically think: "If ret < 0 then certainly it is < the offset of
some internal field. So why perform two comparisons when one is
enough?"
To help such a reader understand what is happening, you could add a
comment like:
/*
* offsetof returns an unsigned value, so the comparison with
* ret uses unsigned arithmetic and won't detect a negative
* error value. We need a separate test for errors.
*/
If you think a comment like this is preferable to a typecast, fine.
Another alternative is:
ret -= offsetof(...);
if (ret < 0)
return 0;
which may look more complicated but allows you to simplify the max3
computation in the next line.
Alan Stern
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2021-10-18 14:38 UTC | newest]
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2021-10-18 14:15 ` [PATCH v2 1/2] HID: u2fzero: explicitly check for errors Alan Stern
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