net: Fix data corruption when splicing from sockets.
The trick in socket splicing where we try to convert the skb->data into a page based reference using virt_to_page() does not work so well. The idea is to pass the virt_to_page() reference via the pipe buffer, and refcount the buffer using a SKB reference. But if we are splicing from a socket to a socket (via sendpage) this doesn't work. The from side processing will grab the page (and SKB) references. The sendpage() calls will grab page references only, return, and then the from side processing completes and drops the SKB ref. The page based reference to skb->data is not enough to keep the kmalloc() buffer backing it from being reused. Yet, that is all that the socket send side has at this point. This leads to data corruption if the skb->data buffer is reused by SLAB before the send side socket actually gets the TX packet out to the device. The fix employed here is to simply allocate a page and copy the skb->data bytes into that page. This will hurt performance, but there is no clear way to fix this properly without a copy at the present time, and it is important to get rid of the data corruption. With fixes from Herbert Xu. Tested-by: NWilly Tarreau <w@1wt.eu> Foreseen-by: NChangli Gao <xiaosuo@gmail.com> Diagnosed-by: NWilly Tarreau <w@1wt.eu> Reported-by: NWilly Tarreau <w@1wt.eu> Fixed-by: NJens Axboe <jens.axboe@oracle.com> Signed-off-by: NJarek Poplawski <jarkao2@gmail.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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