On Mon, Jul 12, 2021 at 11:38:43AM -0700, Brian Norris wrote:

On Sun, Jul 11, 2021 at 6:43 PM Pkshih [off-list ref] wrote:

quoted

quoted

-----Original Message-----
From: Len Baker [mailto:len.baker@gmx.com]

In the rtw_pci_init_rx_ring function the "if (len > TRX_BD_IDX_MASK)"
statement guarantees that len is less than or equal to GENMASK(11, 0) or
in other words that len is less than or equal to 4095. However the
rx_ring->buf has a size of RTK_MAX_RX_DESC_NUM (defined as 512). This
way it is possible an out-of-bounds write in the for statement due to
the i variable can exceed the rx_ring->buff size.

Fix it using the ARRAY_SIZE macro.

Cc: stable@vger.kernel.org
Addresses-Coverity-ID: 1461515 ("Out-of-bounds write")

Coverity seems to be giving a false warning here. I presume it's
taking the |len| comparison as proof that |len| might be as large as
TRX_BD_IDX_MASK, but as noted below, that's not really true; the |len|
comparison is really just dead code.

I agree.

quoted

quoted

Fixes: e3037485c68ec ("rtw88: new Realtek 802.11ac driver")
Signed-off-by: Len Baker <redacted>

quoted

To prevent the 'len' argument from exceeding the array size of rx_ring->buff, I
suggest to add another checking statement, like

        if (len > ARRAY_SIZE(rx_ring->buf)) {
                rtw_err(rtwdev, "len %d exceeds maximum RX ring buffer\n", len);
                return -EINVAL;
        }

That seems like a better idea, if we really need to patch anything.

I think it is reasonable to protect any potencial overflow (for example, if
this function is used in the future with a parameter greater than 512). It
is better to be defensive in this case :)

quoted

But, I wonder if this a false alarm because 'len' is equal to ARRAY_SIZE(rx_ring->buf)
for now.

Or to the point: rtw_pci_init_rx_ring() is only ever called with a
fixed constant -- RTK_MAX_RX_DESC_NUM (i.e., 512) -- so the alleged
overflow cannot happen.

Brian

I will send a v2 for review.

Thanks,
Len