Re: [PATCH] net/ipv4: return the real errno instead of -EINVAL

From: Vadim Fedorenko
Date: Fri Aug 04 2023 - 16:57:21 EST


On 04/08/2023 09:48, yang.yang29@xxxxxxxxxx wrote:
From: xu xin <xu.xin16@xxxxxxxxxx>

For now, no matter what error pointer ip_neigh_for_gw() returns,
ip_finish_output2() always return -EINVAL, which may mislead the upper
users.

For exemple, an application uses sendto to send an UDP packet, but when the
neighbor table overflows, sendto() will get a value of -EINVAL, and it will
cause users to waste a lot of time checking parameters for errors.

Return the real errno instead of -EINVAL.

Signed-off-by: xu xin <xu.xin16@xxxxxxxxxx>
Reviewed-by: Yang Yang <yang.yang29@xxxxxxxxxx>
Cc: Si Hao <si.hao@xxxxxxxxxx>
Cc: Dai Shixin <dai.shixin@xxxxxxxxxx>
Cc: Jiang Xuexin <jiang.xuexin@xxxxxxxxxx>
---
net/ipv4/ip_output.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 6ba1a0fafbaa..2d7cf083dff9 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -201,6 +201,7 @@ static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *s
unsigned int hh_len = LL_RESERVED_SPACE(dev);
struct neighbour *neigh;
bool is_v6gw = false;
+ int res;

if (rt->rt_type == RTN_MULTICAST) {
IP_UPD_PO_STATS(net, IPSTATS_MIB_OUTMCAST, skb->len);
@@ -214,8 +215,7 @@ static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *s
}

if (lwtunnel_xmit_redirect(dst->lwtstate)) {
- int res = lwtunnel_xmit(skb);
-
+ res = lwtunnel_xmit(skb);
if (res < 0 || res == LWTUNNEL_XMIT_DONE)
return res;
}
@@ -223,8 +223,6 @@ static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *s
rcu_read_lock();
neigh = ip_neigh_for_gw(rt, skb, &is_v6gw);
if (!IS_ERR(neigh)) {
- int res;
-
sock_confirm_neigh(skb, neigh);
/* if crossing protocols, can not use the cached header */
res = neigh_output(neigh, skb, is_v6gw);
@@ -236,7 +234,8 @@ static int ip_finish_output2(struct net *net, struct sock *sk, struct sk_buff *s
net_dbg_ratelimited("%s: No header cache and no neighbour!\n",
__func__);
kfree_skb_reason(skb, SKB_DROP_REASON_NEIGH_CREATEFAIL);
- return -EINVAL;
+ res = PTR_ERR(neigh);
+ return res;

I believe this part could be written as

- return -EINVAL;
+ return PTR_ERR(neigh);


and there is no need to change the code is other places. This will be
easier to track/backport.


}

static int ip_finish_output_gso(struct net *net, struct sock *sk,