Subject: [PATCH net-next] udp: Fix kernel panic in UDP GSO path

From: Sean Tranchetti <[email-masked]>
Date: Thu, 10 May 2018 18:38:47 -0600

Using GSO in the UDP path on a device with
scatter-gather netdevice feature disabled will result in a kernel
panic with the following call stack:

kernel BUG at net/core/skbuff.c:104!
Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
PC is at skb_panic+0x4c/0x54
LR is at skb_panic+0x4c/0x54
Process udpgso_bench_tx (pid: 4078, stack limit = 0xffffff8048de8000)
[<ffffff96e8790378>] skb_panic+0x4c/0x54
[<ffffff96e8788b54>] skb_copy_bits+0x0/0x244
[<ffffff96e8836088>] __ip_append_data+0x230/0x814
[<ffffff96e8837090>] ip_make_skb+0xe4/0x178
[<ffffff96e8865444>] udp_sendmsg+0x828/0x888
[<ffffff96e8872818>] inet_sendmsg+0xe4/0x130
[<ffffff96e877c894>] ___sys_sendmsg+0x1d8/0x2c0
[<ffffff96e877ca0c>] SyS_sendmsg+0x90/0xe0

This panic is the result of allocating SKBs with small size
for the newly segmented SKB. If the scatter-gather feature is
disabled, the code attempts to call skb_put() on the small SKB
with an argument of nearly the entire unsegmented SKB length.

After this patch, attempting to use GSO with scatter-gather
disabled will result in -EINVAL being returned.

Fixes: 15e36f5b8e98 ("udp: paged allocation with gso")
Signed-off-by: Sean Tranchetti <[email-masked]>
Signed-off-by: Subash Abhinov Kasiviswanathan <[email-masked]>
---
 net/ipv4/ip_output.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index b5e21eb..0d63690 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -1054,8 +1054,16 @@ static int __ip_append_data(struct sock *sk,
 			copy = length;
 
 		if (!(rt->dst.dev->features&NETIF_F_SG)) {
+			struct sk_buff *tmp;
 			unsigned int off;
 
+			if (paged) {
+				err = -EINVAL;
+				while ((tmp = __skb_dequeue(queue)) != NULL)
+					kfree(tmp);
+				goto error;
+			}
+
 			off = skb->len;
 			if (getfrag(from, skb_put(skb, copy),
 					offset, copy, off, skb) < 0) {
-- 
1.9.1