Fix coverity issue 'Resource leak'.

We should clean the skb resource if nlmsg_put/append failed.

Fixes: 738136a0e375 ("netlink: split up copies in the ack construction")
Signed-off-by: Tao Chen <chentao.kernel@linux.alibaba.com>

---
Changes in v2:
  -Fix some comments
  -Use "nlmsg_free" interface
---
 net/netlink/af_netlink.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index c6b8207e..b8afec3 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2500,7 +2500,7 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 
 	skb = nlmsg_new(payload + tlvlen, GFP_KERNEL);
 	if (!skb)
-		goto err_bad_put;
+		goto err_skb;
 
 	rep = nlmsg_put(skb, NETLINK_CB(in_skb).portid, nlh->nlmsg_seq,
 			NLMSG_ERROR, sizeof(*errmsg), flags);
@@ -2528,6 +2528,8 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	return;
 
 err_bad_put:
+	nlmsg_free(skb);
+err_skb:
 	NETLINK_CB(in_skb).sk->sk_err = ENOBUFS;
 	sk_error_report(NETLINK_CB(in_skb).sk);
 }
-- 
2.2.1

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Sat,  5 Nov 2022 17:05:04 +0800 you wrote:
> Fix coverity issue 'Resource leak'.
> 
> We should clean the skb resource if nlmsg_put/append failed.
> 
> Fixes: 738136a0e375 ("netlink: split up copies in the ack construction")
> Signed-off-by: Tao Chen <chentao.kernel@linux.alibaba.com>
> 
> [...]

Here is the summary with links:
  - [net-next,v2] netlink: Fix potential skb memleak in netlink_ack
    https://git.kernel.org/netdev/net-next/c/e69761483361

You are awesome, thank you!
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