On Thu, 19 Sept 2019 at 22:39, <miny...@acm.org> wrote:
>
> From: Corey Minyard <cminy...@mvista.com>
>
> Signed-off-by: Corey Minyard <cminy...@mvista.com>
> ---
Very old patch, but Coverity has decided it doesn't like something
in this function that's still basically the same in the current codebase
(CID 1487146):
> +static int ipmi_write_data(SMBusDevice *dev, uint8_t *buf, uint8_t len)
> +{
> + SMBusIPMIDevice *sid = SMBUS_IPMI(dev);
> + bool send = false;
> + uint8_t cmd;
> + int ret = 0;
> +
> + /* length is guaranteed to be >= 1. */
> + cmd = *buf++;
> + len--;
> +
> + /* Handle read request, which don't have any data in the write part. */
> + switch (cmd) {
> + case SSIF_IPMI_RESPONSE:
> + sid->currblk = 0;
> + ret = ipmi_load_readbuf(sid);
> + break;
> +
> + case SSIF_IPMI_MULTI_PART_RESPONSE_MIDDLE:
> + sid->currblk++;
> + ret = ipmi_load_readbuf(sid);
> + break;
> +
> + case SSIF_IPMI_MULTI_PART_RETRY:
> + if (len >= 1) {
> + sid->currblk = buf[0];
> + ret = ipmi_load_readbuf(sid);
> + } else {
> + ret = -1;
> + }
> + break;
> +
> + default:
> + break;
> + }
> +
> + /* This should be a message write, make the length is there and correct.
> */
> + if (len >= 1) {
> + if (*buf != len - 1 || *buf > MAX_SSIF_IPMI_MSG_CHUNK) {
> + return -1; /* Bogus message */
> + }
> + buf++;
> + len--;
> + }
After all of this preamble, len can be zero...
> +
> + switch (cmd) {
> + case SSIF_IPMI_REQUEST:
> + send = true;
> + /* FALLTHRU */
> + case SSIF_IPMI_MULTI_PART_REQUEST_START:
> + if (len < 2) {
> + return -1; /* Bogus. */
> + }
> + memcpy(sid->inmsg, buf, len);
> + sid->inlen = len;
> + break;
> +
> + case SSIF_IPMI_MULTI_PART_REQUEST_END:
> + send = true;
> + /* FALLTHRU */
> + case SSIF_IPMI_MULTI_PART_REQUEST_MIDDLE:
> + if (!sid->inlen) {
> + return -1; /* Bogus. */
> + }
> + if (sid->inlen + len > MAX_SSIF_IPMI_MSG_SIZE) {
> + sid->inlen = 0; /* Discard the message. */
> + return -1; /* Bogus. */
> + }
...this error checking on the values of the 'middle' request
means that after one 'middle' request we can end up with
sid->inlen == MAX_SSIF_IPMI_MSG_SIZE (ie we filled the
entire sid->inmsg[] array).
But then if we get another 'middle' request with len == 0,
that will pass this error checking because (sid->inlen + len == MSG_SIZE)
and fall through into...
> + if (len < 32) {
> + /*
> + * Special hack, a multi-part middle that is less than 32 bytes
> + * marks the end of a message. The specification is fairly
> + * confusing, so some systems to this, even sending a zero
> + * length end message to mark the end.
> + */
> + send = true;
> + }
> + memcpy(sid->inmsg + sid->inlen, buf, len);
...calling memcpy() with argument 1 being a pointer that points
one past the end of the array. Even though len will be 0 and
we won't memcpy() anything, this is (depending on how you choose
to intepret things the C standard doesn't come right out and state
explicitly) undefined behaviour, because memcpy() wants to be passed
valid pointers, even if you ask it to do no work with a zero len.
This isn't going to be a visible bug in practical terms, but it would
make Coverity happy if we either (a) rejected a request with an empty
length or else (b) skipped the memcpy(). I don't know enough about
IPMI to know which is better.
> + sid->inlen += len;
> + break;
> + }
> +
> + if (send && sid->inlen) {
> + smbus_ipmi_send_msg(sid);
> + }
> +
> + return ret;
> +}
thanks
-- PMM
