netdev - [benet] possible endianness bug in be_cmd_txq

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Message-ID: <20171210164120.GS21978@ZenIV.linux.org.uk>
Date:   Sun, 10 Dec 2017 16:41:20 +0000
From:   Al Viro <viro@...IV.linux.org.uk>
To:     netdev@...r.kernel.org
Cc:     Vasundhara Volam <vasundhara.volam@...lex.com>,
        Sathya Perla <sathya.perla@...lex.com>
Subject: [benet] possible endianness bug in be_cmd_txq_create()

In be_cmd_txq_create() we have
        if (req->hdr.version > 0)
                req->if_id = cpu_to_le16(adapter->if_handle);
        req->num_pages = PAGES_4K_SPANNED(q_mem->va, q_mem->size);
        req->ulp_num = BE_ULP1_NUM;
        req->type = BE_ETH_TX_RING_TYPE_STANDARD;
        req->cq_id = cpu_to_le16(cq->id);
        req->queue_size = be_encoded_q_len(txq->len);
        be_cmd_page_addrs_prepare(req->pages, ARRAY_SIZE(req->pages), q_mem);
        ver = req->hdr.version;

req points to 

struct be_cmd_req_eth_tx_create {
        struct be_cmd_req_hdr hdr;
        u8 num_pages;
        u8 ulp_num;
        u16 type;
        u16 if_id;
        u8 queue_size;
        u8 rsvd0;
        u32 rsvd1;
        u16 cq_id;
        u16 rsvd2;
        u32 rsvd3[13];
        struct phys_addr pages[8];
} __packed;

Everything appears to be consistent with little-endian data - direct
assignments to u8 fields, cpu_to_le16 for cq_id and if_id, phys_addr
array is also filled with little-endian data, so's ->hdr (several
lines prior, by be_wrb_cmd_hdr_prepare()).

The only exception is
        req->type = BE_ETH_TX_RING_TYPE_STANDARD;
where we set a 16bit field with host-endian constant (2).

benet is playing silly buggers with swap-in-place in some places, but
it's always 32bit values getting swapped, so this can't be happening
here (num_pages, ulp_num and type form a 32bit-aligned word, and
on big-endian cpu_to_le32() done to it would've ended up with num_pages = 2,
ulp_num = 0, type = 256 + PAGES_4K_SPANNED(q_mem->va, q_mem->size), which is
unlikely to do anything good).

So it really smells like this line should've been
        req->type = cpu_to_le16(BE_ETH_TX_RING_TYPE_STANDARD);

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.