Re: [PATCH net] net: check the minimum value of gso size in virtio_net_hdr_to_skb()
From: Wang Liang
Date: Tue Jul 29 2025 - 08:23:05 EST
在 2025/7/25 16:55, Xuan Zhuo 写道:
On Thu, 24 Jul 2025 16:30:05 +0800, Wang Liang <wangliang74@xxxxxxxxxx> wrote:
When sending a packet with virtio_net_hdr to tun device, if the gso_type
in virtio_net_hdr is SKB_GSO_UDP and the gso_size is less than udphdr
size, below crash may happen.
------------[ cut here ]------------
kernel BUG at net/core/skbuff.c:4572!
Oops: invalid opcode: 0000 [#1] SMP NOPTI
CPU: 0 UID: 0 PID: 62 Comm: mytest Not tainted 6.16.0-rc7 #203 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
RIP: 0010:skb_pull_rcsum+0x8e/0xa0
Code: 00 00 5b c3 cc cc cc cc 8b 93 88 00 00 00 f7 da e8 37 44 38 00 f7 d8 89 83 88 00 00 00 48 8b 83 c8 00 00 00 5b c3 cc cc cc cc <0f> 0b 0f 0b 66 66 2e 0f 1f 84 00 000
RSP: 0018:ffffc900001fba38 EFLAGS: 00000297
RAX: 0000000000000004 RBX: ffff8880040c1000 RCX: ffffc900001fb948
RDX: ffff888003e6d700 RSI: 0000000000000008 RDI: ffff88800411a062
RBP: ffff8880040c1000 R08: 0000000000000000 R09: 0000000000000001
R10: ffff888003606c00 R11: 0000000000000001 R12: 0000000000000000
R13: ffff888004060900 R14: ffff888004050000 R15: ffff888004060900
FS: 000000002406d3c0(0000) GS:ffff888084a19000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000040 CR3: 0000000004007000 CR4: 00000000000006f0
Call Trace:
<TASK>
udp_queue_rcv_one_skb+0x176/0x4b0 net/ipv4/udp.c:2445
udp_queue_rcv_skb+0x155/0x1f0 net/ipv4/udp.c:2475
udp_unicast_rcv_skb+0x71/0x90 net/ipv4/udp.c:2626
__udp4_lib_rcv+0x433/0xb00 net/ipv4/udp.c:2690
ip_protocol_deliver_rcu+0xa6/0x160 net/ipv4/ip_input.c:205
ip_local_deliver_finish+0x72/0x90 net/ipv4/ip_input.c:233
ip_sublist_rcv_finish+0x5f/0x70 net/ipv4/ip_input.c:579
ip_sublist_rcv+0x122/0x1b0 net/ipv4/ip_input.c:636
ip_list_rcv+0xf7/0x130 net/ipv4/ip_input.c:670
__netif_receive_skb_list_core+0x21d/0x240 net/core/dev.c:6067
netif_receive_skb_list_internal+0x186/0x2b0 net/core/dev.c:6210
napi_complete_done+0x78/0x180 net/core/dev.c:6580
tun_get_user+0xa63/0x1120 drivers/net/tun.c:1909
tun_chr_write_iter+0x65/0xb0 drivers/net/tun.c:1984
vfs_write+0x300/0x420 fs/read_write.c:593
ksys_write+0x60/0xd0 fs/read_write.c:686
do_syscall_64+0x50/0x1c0 arch/x86/entry/syscall_64.c:63
</TASK>
To trigger gso segment in udp_queue_rcv_skb(), we should also set option
UDP_ENCAP_ESPINUDP to enable udp_sk(sk)->encap_rcv. When the encap_rcv
hook return 1 in udp_queue_rcv_one_skb(), udp_csum_pull_header() will try
to pull udphdr, but the skb size has been segmented to gso size, which
leads to this crash.
Is it correct to access the checksum of a segmented skb?
Only udp has this probloem. Add check for the minimum value of gso size in
virtio_net_hdr_to_skb().
Why tcp has not this problem?
Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection")
Fixes: 3d010c8031e3 ("udp: do not accept non-tunnel GSO skbs landing in a tunnel")
Signed-off-by: Wang Liang <wangliang74@xxxxxxxxxx>
---
include/linux/virtio_net.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index 02a9f4dc594d..0533101642bd 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -157,11 +157,13 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
u16 gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size);
unsigned int nh_off = p_off;
struct skb_shared_info *shinfo = skb_shinfo(skb);
+ u16 min_gso_size = 0;
switch (gso_type & ~SKB_GSO_TCP_ECN) {
case SKB_GSO_UDP:
/* UFO may not include transport header in gso_size. */
nh_off -= thlen;
+ min_gso_size = sizeof(struct udphdr) + 1;
break;
case SKB_GSO_UDP_L4:
if (!(hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM))
@@ -172,6 +174,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
return -EINVAL;
if (gso_type != SKB_GSO_UDP_L4)
return -EINVAL;
+ min_gso_size = sizeof(struct udphdr) + 1;
why +1?
Thanks.
Hi! Sorry for replying so late.
The first patch should add RFC, because I am not sure it is the best fix
method. Set 'min_gso_size = sizeof(struct udphdr) + 1;' to ensure at least
one byte in payload.
After discussions in mail list, I send a v2 patch, please check it:
https://lore.kernel.org/netdev/20250729123907.3318425-1-wangliang74@xxxxxxxxxx/T/#u
Thanks.
break;
case SKB_GSO_TCPV4:
case SKB_GSO_TCPV6:
@@ -182,7 +185,7 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
}
/* Kernel has a special handling for GSO_BY_FRAGS. */
- if (gso_size == GSO_BY_FRAGS)
+ if ((gso_size == GSO_BY_FRAGS) || (gso_size < min_gso_size))
return -EINVAL;
/* Too small packets are not really GSO ones. */
--
2.34.1