[PATCH net] net: psample: fix info leak in PSAMPLE_ATTR_DATA

[Jakub Kicinski <kuba@kernel.org>]

psample open codes nla_put() presumably to avoid wiping
the data with 0s just to override it with packet data.
This open coding is missing clearing the pad, however,
each netlink attr is padded to 4B and data_len may
not be divisible by 4B.

Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: yotam.gi@gmail.com
CC: jhs@mojatatu.com
CC: jiri@resnulli.us
---
 net/psample/psample.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/psample/psample.c b/net/psample/psample.c
index 7763662036fb..c112e1f0ccac 100644
--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -476,15 +476,17 @@ void psample_sample_packet(struct psample_group *group,
 		goto error;
 
 	if (data_len) {
-		int nla_len = nla_total_size(data_len);
+		int nla_len = nla_attr_size(data_len);
 		struct nlattr *nla;
 
 		nla = skb_put(nl_skb, nla_len);
 		nla->nla_type = PSAMPLE_ATTR_DATA;
-		nla->nla_len = nla_attr_size(data_len);
+		nla->nla_len = nla_len;
 
 		if (skb_copy_bits(skb, 0, nla_data(nla), data_len))
 			goto error;
+
+		skb_put_zero(nl_skb, nla_padlen(data_len));
 	}
 
 #ifdef CONFIG_INET
-- 
2.54.0