<div dir="auto">That's to make sure a minimum width so that packages shorter than expected dont have issues with the functions accessing it beyond the buffer. <div dir="auto"><br></div><div dir="auto">Oversize will just adapt anyway.</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, 25 Mar 2025, 17:49 Michael Balzer via OvmsDev, <<a href="mailto:ovmsdev@lists.openvehicles.com">ovmsdev@lists.openvehicles.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div>
I see you already checked the poll handlers don't write to the
buffer, so that's a possible & better option.<br>
<br>
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.<br>
<br>
Regards,<br>
Michael<br>
<br>
<br>
<div>Am 25.03.25 um 09:54 schrieb Michael
Geddes via OvmsDev:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>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 </div>
<div>in the code won't fumble into uncharted space and we get
rid of the unchecked copy into the static memory space? </div>
<div><br>
</div>
<div>//.ichael</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, 25 Mar 2025 at 16:38,
Michael Balzer via OvmsDev <<a href="mailto:ovmsdev@lists.openvehicles.com" target="_blank" rel="noreferrer">ovmsdev@lists.openvehicles.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Wayne,<br>
<br>
uh, yes, that's a typical buffer overflow pattern there,
unguarded <br>
copying of a string contents to a fixed size buffer:<br>
<br>
> static uint8_t buf[MAX_POLL_DATA_LEN];<br>
> memcpy(buf, rxbuf.c_str(), rxbuf.size());<br>
<br>
Not sure why/if the handlers need an uint8_t array in the
first place, <br>
but a quick first fix should be to adjust MAX_POLL_DATA_LEN:<br>
<br>
> #define MAX_POLL_DATA_LEN 196<br>
<br>
Add some spare room to the 329 bytes needed, just in case.<br>
<br>
Regards,<br>
Michael<br>
<br>
<br>
Am 25.03.25 um 09:31 schrieb Wayne Love:<br>
> Hi Micheal,<br>
><br>
> Your comment...<br>
><br>
>> Regarding Leaf CAN problems there ist a running
investigation here: <br>
>> <a href="https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/issues/980" rel="noreferrer noreferrer" target="_blank">https://github.com/openvehicles/Open-Vehicle-Monitoring-System-3/issues/980</a><br>
><br>
> Is dead on the money.<br>
><br>
> Polling group 61 returns an abnormally large response,
329 bytes. <br>
> This causes a buffer overrun in <br>
> OvmsVehicleNissanLeaf::IncomingPollReply with an
unguarded memcpy that <br>
> causes the module to crash. Once the module crashes, I
get the exact <br>
> symptoms in issue 980.<br>
><br>
> Appreciate your help with this.<br>
><br>
> Thanks<br>
> Wayne<br>
><br>
><br>
><br>
<br>
-- <br>
Michael Balzer * <a href="https://www.google.com/maps/search/Am+Rahmen+5+*+D-58313+Herdecke?entry=gmail&source=g">Am Rahmen 5 * D-58313 Herdecke</a><br>
Fon 02330 9104094 * Handy 0176 20698926<br>
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