6.12-stable review patch. If anyone has any objections, please let me know.
------------------
From: Wang Liang wangliang74@huawei.com
[ Upstream commit d46e51f1c78b9ab9323610feb14238d06d46d519 ]
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.
Previous commit cf329aa42b66 ("udp: cope with UDP GRO packet misdirection") introduces segmentation in UDP receive path only for GRO, which was never intended to be used for UFO, so drop UFO packets in udp_rcv_segment().
Link: https://lore.kernel.org/netdev/20250724083005.3918375-1-wangliang74@huawei.c... Link: https://lore.kernel.org/netdev/20250729123907.3318425-1-wangliang74@huawei.c... Fixes: cf329aa42b66 ("udp: cope with UDP GRO packet misdirection") Suggested-by: Willem de Bruijn willemdebruijn.kernel@gmail.com Signed-off-by: Wang Liang wangliang74@huawei.com Reviewed-by: Willem de Bruijn willemb@google.com Link: https://patch.msgid.link/20250730101458.3470788-1-wangliang74@huawei.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/net/udp.h | 24 ++++++++++++++++++------ 1 file changed, 18 insertions(+), 6 deletions(-)
diff --git a/include/net/udp.h b/include/net/udp.h index 61222545ab1c..0b2e3a5e01d8 100644 --- a/include/net/udp.h +++ b/include/net/udp.h @@ -461,6 +461,16 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk, { netdev_features_t features = NETIF_F_SG; struct sk_buff *segs; + int drop_count; + + /* + * Segmentation in UDP receive path is only for UDP GRO, drop udp + * fragmentation offload (UFO) packets. + */ + if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP) { + drop_count = 1; + goto drop; + }
/* Avoid csum recalculation by skb_segment unless userspace explicitly * asks for the final checksum values @@ -484,16 +494,18 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk, */ segs = __skb_gso_segment(skb, features, false); if (IS_ERR_OR_NULL(segs)) { - int segs_nr = skb_shinfo(skb)->gso_segs; - - atomic_add(segs_nr, &sk->sk_drops); - SNMP_ADD_STATS(__UDPX_MIB(sk, ipv4), UDP_MIB_INERRORS, segs_nr); - kfree_skb(skb); - return NULL; + drop_count = skb_shinfo(skb)->gso_segs; + goto drop; }
consume_skb(skb); return segs; + +drop: + atomic_add(drop_count, &sk->sk_drops); + SNMP_ADD_STATS(__UDPX_MIB(sk, ipv4), UDP_MIB_INERRORS, drop_count); + kfree_skb(skb); + return NULL; }
static inline void udp_post_segment_fix_csum(struct sk_buff *skb)