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netlink: Add answer_flags to netlink_callback

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With dump filtering we need a way to ensure the NLM_F_DUMP_FILTERED
flag is set on a message back to the user if the data returned is
influenced by some input attributes. Normally this can be done as
messages are added to the skb, but if the filter results in no data
being returned, the user could be confused as to why.

This patch adds answer_flags to the netlink_callback allowing dump
handlers to set the NLM_F_DUMP_FILTERED at a minimum in the
NLMSG_DONE message ensuring the flag gets back to the user.

The netlink_callback space is initialized to 0 via a memset in
__netlink_dump_start, so init of the new answer_flags is covered.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Ahern 2018-10-15 18:56:41 -07:00 committed by David S. Miller
parent e85679511e
commit 22e6c58b8c
2 changed files with 3 additions and 1 deletions
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1
include/linux/netlink.h
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@ -180,6 +180,7 @@ struct netlink_callback {
u16 family;
u16 min_dump_alloc;
bool strict_check;
u16 answer_flags;
unsigned int prev_seq, seq;
long args[6];
};

3
net/netlink/af_netlink.c
View File

@ -2257,7 +2257,8 @@ static int netlink_dump(struct sock *sk)
}
nlh = nlmsg_put_answer(skb, cb, NLMSG_DONE,
sizeof(nlk->dump_done_errno), NLM_F_MULTI);
sizeof(nlk->dump_done_errno),
NLM_F_MULTI | cb->answer_flags);
if (WARN_ON(!nlh))
goto errout_skb;