[Ovmsdev] Leaf AZE1 Can1 stuck after poll 7BB group 61

[Michael Balzer]

I see you already checked the poll handlers don't write to the buffer, 
so that's a possible & better option.

But why do you limit the reserve() call? Clearly, the MAX_POLL_DATA_LEN 
isn't sufficient for the new poll, Wayne wants to add. Doing 
rxbuf.reserve(length + job.mlremain) should be perfectly OK, as it 
adapts to any reply size? After all, it's just a reservation, append 
will need to reallocate if it's too small. I think the module can get 
rid off MAX_POLL_DATA_LEN altogether when using the string memory directly.

Regards,
Michael


Am 25.03.25 um 09:54 schrieb Michael Geddes via OvmsDev:
> Why don't we just std:max() the  reserve() on the string and cast 
> c_str() to uint8_t * !?  That way we know the array access
> in the code won't fumble into uncharted space and we get rid of the 
> unchecked copy into the static memory space?
>
> //.ichael
>
> On Tue, 25 Mar 2025 at 16:38, Michael Balzer via OvmsDev 
> <ovmsdev at lists.openvehicles.com> wrote:
>
>     Wayne,
>
>     uh, yes, that's a typical buffer overflow pattern there, unguarded
>     copying of a string contents to a fixed size buffer:
>
>     >   static uint8_t buf[MAX_POLL_DATA_LEN];
>     >   memcpy(buf, rxbuf.c_str(), rxbuf.size());
>
>     Not sure why/if the handlers need an uint8_t array in the first
>     place,
>     but a quick first fix should be to adjust MAX_POLL_DATA_LEN:
>
>     > #define MAX_POLL_DATA_LEN         196
>
>     Add some spare room to the 329 bytes needed, just in case.
>
>     Regards,
>     Michael
>
>
>     Am 25.03.25 um 09:31 schrieb Wayne Love:
>     > Hi Micheal,
>     >
>     > Your comment...
>     >
>     >> Regarding Leaf CAN problems there ist a running investigation
>     here:
>     >>
>     https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/issues/980
>     >
>     > Is dead on the money.
>     >
>     > Polling group 61 returns an abnormally large response, 329 bytes.
>     > This causes a buffer overrun in
>     > OvmsVehicleNissanLeaf::IncomingPollReply with an unguarded
>     memcpy that
>     > causes the module to crash.  Once the module crashes, I get the
>     exact
>     > symptoms in issue 980.
>     >
>     > Appreciate your help with this.
>     >
>     > Thanks
>     > Wayne
>     >
>     >
>     >
>
>     -- 
>     Michael Balzer * Am Rahmen 5 * D-58313 Herdecke
>     Fon 02330 9104094 * Handy 0176 20698926
>
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-- 
Michael Balzer * Am Rahmen 5 * D-58313 Herdecke
Fon 02330 9104094 * Handy 0176 20698926

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