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SubjectRe: [PATCH 4.9 03/63] 9p/net: Fix zero-copy path in the 9p virtio transport
On Fri, Sep 7, 2018 at 2:34 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> 4.9-stable review patch. If anyone has any objections, please let me know.
>

Do your scripts have a bad hair day ? The subject says 4.18.

Guenter

> ------------------
>
> From: Chirantan Ekbote <chirantan@chromium.org>
>
> commit d28c756caee6e414d9ba367d0b92da24145af2a8 upstream.
>
> The zero-copy optimization when reading or writing large chunks of data
> is quite useful. However, the 9p messages created through the zero-copy
> write path have an incorrect message size: it should be the size of the
> header + size of the data being written but instead it's just the size
> of the header.
>
> This only works if the server ignores the size field of the message and
> otherwise breaks the framing of the protocol. Fix this by re-writing the
> message size field with the correct value.
>
> Tested by running `dd if=/dev/zero of=out bs=4k count=1` inside a
> virtio-9p mount.
>
> Link: http://lkml.kernel.org/r/20180717003529.114368-1-chirantan@chromium.org
> Signed-off-by: Chirantan Ekbote <chirantan@chromium.org>
> Reviewed-by: Greg Kurz <groug@kaod.org>
> Tested-by: Greg Kurz <groug@kaod.org>
> Cc: Dylan Reid <dgreid@chromium.org>
> Cc: Guenter Roeck <groeck@chromium.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
> net/9p/trans_virtio.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> --- a/net/9p/trans_virtio.c
> +++ b/net/9p/trans_virtio.c
> @@ -406,6 +406,7 @@ p9_virtio_zc_request(struct p9_client *c
> p9_debug(P9_DEBUG_TRANS, "virtio request\n");
>
> if (uodata) {
> + __le32 sz;
> int n = p9_get_mapped_pages(chan, &out_pages, uodata,
> outlen, &offs, &need_drop);
> if (n < 0)
> @@ -416,6 +417,12 @@ p9_virtio_zc_request(struct p9_client *c
> memcpy(&req->tc->sdata[req->tc->size - 4], &v, 4);
> outlen = n;
> }
> + /* The size field of the message must include the length of the
> + * header and the length of the data. We didn't actually know
> + * the length of the data until this point so add it in now.
> + */
> + sz = cpu_to_le32(req->tc->size + outlen);
> + memcpy(&req->tc->sdata[0], &sz, sizeof(sz));
> } else if (uidata) {
> int n = p9_get_mapped_pages(chan, &in_pages, uidata,
> inlen, &offs, &need_drop);
>
>

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