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. Oversize will just adapt anyway. On Tue, 25 Mar 2025, 17:49 Michael Balzer via OvmsDev, < ovmsdev@lists.openvehicles.com> wrote:
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@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
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