Currently, ACK in case of error contains a full copy of the originating
message. This can cause lost ACKs with large netlink messages, especially
after commit c05cdb1b864f ("netlink: allow large data transfers from
user-space").
Send back a capped message instead.
Signed-off-by: Christophe Ricard <christophe-h.ric...@st.com>
---
net/netlink/af_netlink.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 67d2104..9df862c 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -85,6 +85,9 @@ struct listeners {
#define NETLINK_F_RECV_NO_ENOBUFS 0x8
#define NETLINK_F_LISTEN_ALL_NSID 0x10
+/* Arbitrary value for a small message less than PAGE_SIZE */
+#define NETLINK_ERR_MESSAGE_CAP 128
+
static inline int netlink_is_kernel(struct sock *sk)
{
return nlk_sk(sk)->flags & NETLINK_F_KERNEL_SOCKET;
@@ -2873,10 +2876,15 @@ void netlink_ack(struct sk_buff *in_skb, struct
nlmsghdr *nlh, int err)
struct nlmsghdr *rep;
struct nlmsgerr *errmsg;
size_t payload = sizeof(*errmsg);
+ size_t size = 0;
- /* error messages get the original request appened */
- if (err)
- payload += nlmsg_len(nlh);
+ /* error messages get a cap request appened */
+ if (err) {
+ payload += nlmsg_len(nlh) > NETLINK_ERR_MESSAGE_CAP ?
+ NETLINK_ERR_MESSAGE_CAP : nlmsg_len(nlh);
+ size = nlmsg_len(nlh) > NETLINK_ERR_MESSAGE_CAP ?
+ (NETLINK_ERR_MESSAGE_CAP + NLMSG_HDRLEN) : nlh->nlmsg_len;
+ }
skb = netlink_alloc_skb(in_skb->sk, nlmsg_total_size(payload),
NETLINK_CB(in_skb).portid, GFP_KERNEL);
@@ -2898,7 +2906,8 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr
*nlh, int err)
NLMSG_ERROR, payload, 0);
errmsg = nlmsg_data(rep);
errmsg->error = err;
- memcpy(&errmsg->msg, nlh, err ? nlh->nlmsg_len : sizeof(*nlh));
+
+ memcpy(&errmsg->msg, nlh, err ? size : sizeof(*nlh));
netlink_unicast(in_skb->sk, skb, NETLINK_CB(in_skb).portid,
MSG_DONTWAIT);
}
EXPORT_SYMBOL(netlink_ack);
--
2.1.4
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