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question about map_read_chunks()

DISCUSSION Tom Tucker 1 participant 1 message Feb 20, 2012 1 message not in the archive

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Tom Tucker

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Hi Dan,

Quoted 8 lines

----- Forwarded message from Dan Carpenter<[email protected]> -----

Date: Mon, 20 Feb 2012 12:50:19 +0300
From: Dan Carpenter<[email protected]>
To: Tom Tucker<[email protected]>
Cc: "J. Bruce Fields"<[email protected]>, [email protected], [email protected]
Subject: question about map_read_chunks()

Quoted 7 lines

I had a couple questions about some map_read_chunks().

net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

    150          ch_bytes = ntohl(ch->rc_target.rs_length);
                 ^^^^^^^^

It look like this is 32 bits from the network?

Yes, it is. All these values should be clamped by the wsize/rsize, however, I don't think we enforce that. We should add a check to svc_rdma_xdr_decode_req().

Quoted 10 lines
    151          head->arg.head[0] = rqstp->rq_arg.head[0];
    152          head->arg.tail[0] = rqstp->rq_arg.tail[0];
    153          head->arg.pages =&head->pages[head->count];
    154          head->hdr_count = head->count; /* save count of hdr pages */
    155          head->arg.page_base = 0;
    156          head->arg.page_len = ch_bytes;
    157          head->arg.len = rqstp->rq_arg.len + ch_bytes;
                                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Can overflow.

Without the proposed check, it can.

Quoted 4 lines
    158          head->arg.buflen = rqstp->rq_arg.buflen + ch_bytes;
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Same. I didn't follow it through to see if an overflow matters. Does it?

I think it could cause bad things to happen, yes.

Quoted 10 lines
    159          head->count++;
    160          chl_map->ch[0].start = 0;
    161          while (byte_count) {
    162                  rpl_map->sge[sge_no].iov_base =
    163                          page_address(rqstp->rq_arg.pages[page_no]) + page_off;
    164                  sge_bytes = min_t(int, PAGE_SIZE-page_off, ch_bytes);
                                           ^^^

This is the wrong cast to use. A large ch_bytes would be counted as a negative value and get around the cap here.

I suppose, in theory, we could have a r/wsize > 2G, in which case, you are correct.

Quoted 5 lines
    165                  rpl_map->sge[sge_no].iov_len = sge_bytes;

regards,
dan carpenter

I think adding a check to svc_rdma_xdr_decode_req() would avoid any possibility of overflow. I'll code up a patch.

Thanks,
Tom