Re: [PATCH net] net: psample: Fix the netlink skb length

On 2/4/2021 10:21 AM, Jakub Kicinski wrote:

On Wed,  3 Feb 2021 11:10:28 +0800 Chris Mi wrote:

quoted

Currently, the netlink skb length only includes metadata and data
length. It doesn't include the psample generic netlink header length.

But what's the bug? Did you see oversized messages on the socket?

Yes.

  Did
one of the nla_put() fail?

Yes.

quoted

Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling")
CC: Yotam Gigi <yotam.gi@gmail.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Chris Mi <redacted>
---
  net/psample/psample.c | 10 ++++++----
  1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/net/psample/psample.c b/net/psample/psample.c
index 33e238c965bd..807d75f5a40f 100644
--- a/net/psample/psample.c
+++ b/net/psample/psample.c

@@ -363,6 +363,7 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
  	struct ip_tunnel_info *tun_info;
  #endif
  	struct sk_buff *nl_skb;
+	int header_len;
  	int data_len;
  	int meta_len;
  	void *data;

@@ -381,12 +382,13 @@ void psample_sample_packet(struct psample_group *group, struct sk_buff *skb,
  		meta_len += psample_tunnel_meta_len(tun_info);
  #endif
  
+	/* psample generic netlink header size */
+	header_len = nlmsg_total_size(GENL_HDRLEN + psample_nl_family.hdrsize);

GENL_HDRLEN is already included by genlmsg_new() and fam->hdrsize is 0
/ uninitialized for psample_nl_family. What am I missing? Ido?

Thanks for pointing this out. If so, it seems this patch is incorrect.

quoted

  	data_len = min(skb->len, trunc_size);
-	if (meta_len + nla_total_size(data_len) > PSAMPLE_MAX_PACKET_SIZE)
-		data_len = PSAMPLE_MAX_PACKET_SIZE - meta_len - NLA_HDRLEN
+	if (header_len + meta_len + nla_total_size(data_len) > PSAMPLE_MAX_PACKET_SIZE)
+		data_len = PSAMPLE_MAX_PACKET_SIZE - header_len - meta_len - NLA_HDRLEN
  			    - NLA_ALIGNTO;
-
-	nl_skb = genlmsg_new(meta_len + nla_total_size(data_len), GFP_ATOMIC);
+	nl_skb = genlmsg_new(header_len + meta_len + nla_total_size(data_len), GFP_ATOMIC);
  	if (unlikely(!nl_skb))
  		return;