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    Subject[PATCH 4.15 048/122] net: sched: report if filter is too large to dump
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Roman Kapl <code@rkapl.cz>


    [ Upstream commit 5ae437ad5a2ed573b1ebb04e0afa70b8869f88dd ]

    So far, if the filter was too large to fit in the allocated skb, the
    kernel did not return any error and stopped dumping. Modify the dumper
    so that it returns -EMSGSIZE when a filter fails to dump and it is the
    first filter in the skb. If we are not first, we will get a next chance
    with more room.

    I understand this is pretty near to being an API change, but the
    original design (silent truncation) can be considered a bug.

    Note: The error case can happen pretty easily if you create a filter
    with 32 actions and have 4kb pages. Also recent versions of iproute try
    to be clever with their buffer allocation size, which in turn leads to

    Signed-off-by: Roman Kapl <code@rkapl.cz>
    Acked-by: Jiri Pirko <jiri@mellanox.com>
    Acked-by: Cong Wang <xiyou.wangcong@gmail.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/sched/cls_api.c | 7 ++++++-
    1 file changed, 6 insertions(+), 1 deletion(-)

    --- a/net/sched/cls_api.c
    +++ b/net/sched/cls_api.c
    @@ -1054,13 +1054,18 @@ static int tc_dump_tfilter(struct sk_buf
    nla_get_u32(tca[TCA_CHAIN]) != chain->index)
    continue;
    if (!tcf_chain_dump(chain, q, parent, skb, cb,
    - index_start, &index))
    + index_start, &index)) {
    + err = -EMSGSIZE;
    break;
    + }
    }

    cb->args[0] = index;

    out:
    + /* If we did no progress, the error (EMSGSIZE) is real */
    + if (skb->len == 0 && err)
    + return err;
    return skb->len;
    }


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