netdev - Re: [benet] possible endianness bug in be_cmd_txq

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Date:   Sun, 10 Dec 2017 18:43:08 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     netdev@...r.kernel.org
Cc:     Sathya Perla <sathya.perla@...lex.com>
Subject: Re: [benet] possible endianness bug in be_cmd_txq_create()

On Sun, Dec 10, 2017 at 04:41:20PM +0000, Al Viro wrote:

> I don't have the hardware, so the above is completely untested (caught by
> sparse when trying to do endianness annotations in drivers/net), but it
> does look like it might be worth a look from benet maintainers.

Another very fishy place is be_roce_mcc_cmd().

        req = embedded_payload(wrb);
        resp = embedded_payload(wrb);

        be_wrb_cmd_hdr_prepare(req, hdr->subsystem,
                               hdr->opcode, wrb_payload_size, wrb, NULL);

OK, we'd formed a (little-endian) header in the first 32 bytes of req and
filled wrb->{tag0,tag1,payload_length,embedded}.

        memcpy(req, wrb_payload, wrb_payload_size);
        be_dws_cpu_to_le(req, wrb_payload_size);

... only to overwrite *req with wrb_payload bulk-converted to little-endian.
OK, so it's responsibility of caller to have prepare payload so that it
would form a valid header after byteswap.

        status = be_mcc_notify_wait(adapter);
        if (cmd_status)
                *cmd_status = (status & 0xffff);
        if (ext_status)
                *ext_status = 0;

OK, we submit the resulting wrb and wait for reply.

        memcpy(wrb_payload, resp, sizeof(*resp) + resp->response_length);
        be_dws_le_to_cpu(wrb_payload, sizeof(*resp) + resp->response_length);

Then we copy the response back into caller-supplied buffer, bulk-converting
it from little-endian to host-endian.  Hardware puts little-endian there,
caller wants host-endian.  But... ->response_length is a 32bit value at
offset 8 from the beginning of response.  Is it little-endian or host-endian?
In the former case we are fucked on b-e host - the value we pass to memcpy()
is going to be in hundreds of megabytes...  And everything in response seems
to be little-endian - we certainly include response_length itself into the
area covered by that bulk byteswap.