linux-kernel - [PATCH net] udp: fix segmentation crash for untrusted source packet

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Date: Wed, 13 Mar 2024 21:34:02 +0800
From: Shiming Cheng <shiming.cheng@...iatek.com>
To: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<lena.wang@...iatek.com>, <shiming.cheng@...iatek.com>
Subject: [PATCH net] udp: fix segmentation crash for untrusted source packet

Kernel exception is reported when making udp frag list segmentation.
Backtrace is as below:
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/ipv4/udp_offload.c:229
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/ipv4/udp_offload.c:262
features=features@...ry=19, is_ipv6=false)
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/ipv4/udp_offload.c:289
features=19)
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/ipv4/udp_offload.c:399
features=19)
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/ipv4/af_inet.c:1418
skb@...ry=0x0, features=19, features@...ry=0)
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/core/gso.c:53
tx_path=<optimized out>)
    at out/android15-6.6/kernel-6.6/kernel-6.6/net/core/gso.c:124

This packet's frag list is null while gso_type is not 0. Then it is treated
as a GRO-ed packet and sent to segment frag list. Function call path is
udp_rcv_segment => config features value
    __udpv4_gso_segment  => skb_gso_ok returns false. Here it should be
                            true. Failed reason is features doesn't match
                            gso_type.
        __udp_gso_segment_list
            skb_segment_list => packet is linear with skb->next = NULL
            __udpv4_gso_segment_list_csum => use skb->next directly and
                                             crash happens

In rx-gro-list GRO-ed packet is set gso type as
NETIF_F_GSO_UDP_L4 | NETIF_F_GSO_FRAGLIST in napi_gro_complete. In gso
flow the features should also set them to match with gso_type. Or else it
will always return false in skb_gso_ok. Then it can't discover the
untrusted source packet and result crash in following function.

Fixes: f2696099c6c6 ("udp: Avoid post-GRO UDP checksum recalculation")
Signed-off-by: Shiming Cheng <shiming.cheng@...iatek.com>
Signed-off-by: Lena Wang <lena.wang@...iatek.com>
---
 include/net/udp.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/udp.h b/include/net/udp.h
index 488a6d2babcc..c87baa23b9da 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -464,7 +464,7 @@ void udpv6_encap_enable(void);
 static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
 					      struct sk_buff *skb, bool ipv4)
 {
-	netdev_features_t features = NETIF_F_SG;
+	netdev_features_t features = NETIF_F_SG | NETIF_F_GSO_UDP_L4 | NETIF_F_GSO_FRAGLIST;
 	struct sk_buff *segs;
 
 	/* Avoid csum recalculation by skb_segment unless userspace explicitly
-- 
2.18.0