4.15-stable review patch.  If anyone has any objections, please let me know.


From: Roman Kapl <c...@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 <c...@rkapl.cz>
Acked-by: Jiri Pirko <j...@mellanox.com>
Acked-by: Cong Wang <xiyou.wangc...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@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)
                if (!tcf_chain_dump(chain, q, parent, skb, cb,
-                                   index_start, &index))
+                                   index_start, &index)) {
+                       err = -EMSGSIZE;
+               }
        cb->args[0] = index;
+       /* If we did no progress, the error (EMSGSIZE) is real */
+       if (skb->len == 0 && err)
+               return err;
        return skb->len;

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