From: Willem de Bruijn willemb@google.com

mainline inclusion from mainline-v6.11-rc2 commit 89add40066f9ed9abe5f7f886fe5789ff7e0c50e category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAKQ33 CVE: CVE-2024-43817

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb for GSO packets.

The function already checks that a checksum requested with VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets this might not hold for segs after segmentation.

Syzkaller demonstrated to reach this warning in skb_checksum_help

offset = skb_checksum_start_offset(skb); ret = -EINVAL; if (WARN_ON_ONCE(offset >= skb_headlen(skb)))

By injecting a TSO packet:

WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0 ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774 ip_finish_output_gso net/ipv4/ip_output.c:279 [inline] __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301 iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813 __gre_xmit net/ipv4/ip_gre.c:469 [inline] ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661 __netdev_start_xmit include/linux/netdevice.h:4850 [inline] netdev_start_xmit include/linux/netdevice.h:4864 [inline] xmit_one net/core/dev.c:3595 [inline] dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611 __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261 packet_snd net/packet/af_packet.c:3073 [inline]

The geometry of the bad input packet at tcp_gso_segment:

[ 52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0 [ 52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244 [ 52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0)) [ 52.003050][ T8403] csum(0x60000c7 start=199 offset=1536 ip_summed=3 complete_sw=0 valid=0 level=0)

Mitigate with stricter input validation.

csum_offset: for GSO packets, deduce the correct value from gso_type. This is already done for USO. Extend it to TSO. Let UFO be: udp[46]_ufo_fragment ignores these fields and always computes the checksum in software.

csum_start: finding the real offset requires parsing to the transport header. Do not add a parser, use existing segmentation parsing. Thanks to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. Again test both TSO and USO. Do not test UFO for the above reason, and do not test UDP tunnel offload.

GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be CHECKSUM_NONE since commit 10154dbded6d6 ("udp: Allow GSO transmit from devices with no checksum offload"), but then still these fields are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no need to test for ip_summed == CHECKSUM_PARTIAL first.

This revises an existing fix mentioned in the Fixes tag, which broke small packets with GSO offload, as detected by kselftests.

Link: https://syzkaller.appspot.com/bug?extid=e1db31216c789f552871 Link: https://lore.kernel.org/netdev/20240723223109.2196886-1-kuba@kernel.org Fixes: e269d79c7d35 ("net: missing check virtio") Cc: stable@vger.kernel.org Signed-off-by: Willem de Bruijn willemb@google.com Link: https://patch.msgid.link/20240729201108.1615114-1-willemdebruijn.kernel@gmai... Signed-off-by: Jakub Kicinski kuba@kernel.org Conflicts: include/linux/virtio_net.h [commit e269d79c7d35 ("net: missing check virtio") and fc8b2a619469 ("net: more strict VIRTIO_NET_HDR_GSO_UDP_L4 validation") not merged] Signed-off-by: Zhang Changzhong zhangchangzhong@huawei.com --- include/linux/virtio_net.h | 12 ++++++++++-- net/ipv4/tcp_offload.c | 3 +++ net/ipv4/udp_offload.c | 4 ++++ 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index 6047058..c72e781 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -144,9 +144,17 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, unsigned int nh_off = p_off; struct skb_shared_info *shinfo = skb_shinfo(skb);

- /* UFO may not include transport header in gso_size. */ - if (gso_type & SKB_GSO_UDP) + switch (gso_type & ~SKB_GSO_TCP_ECN) { + case SKB_GSO_UDP: + /* UFO may not include transport header in gso_size. */ nh_off -= thlen; + break; + case SKB_GSO_TCPV4: + case SKB_GSO_TCPV6: + if (skb->csum_offset != offsetof(struct tcphdr, check)) + return -EINVAL; + break; + }

/* Kernel has a special handling for GSO_BY_FRAGS. */ if (gso_size == GSO_BY_FRAGS) diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c index fc61cd3..357d3be 100644 --- a/net/ipv4/tcp_offload.c +++ b/net/ipv4/tcp_offload.c @@ -71,6 +71,9 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb, if (thlen < sizeof(*th)) goto out;

+ if (unlikely(skb_checksum_start(skb) != skb_transport_header(skb))) + goto out; + if (!pskb_may_pull(skb, thlen)) goto out;

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c index 6120df4..884453d 100644 --- a/net/ipv4/udp_offload.c +++ b/net/ipv4/udp_offload.c @@ -274,6 +274,10 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb, if (gso_skb->len <= sizeof(*uh) + mss) return ERR_PTR(-EINVAL);

+ if (unlikely(skb_checksum_start(gso_skb) != + skb_transport_header(gso_skb))) + return ERR_PTR(-EINVAL); + if (skb_gso_ok(gso_skb, features | NETIF_F_GSO_ROBUST)) { /* Packet is from an untrusted source, reset gso_segs. */ skb_shinfo(gso_skb)->gso_segs = DIV_ROUND_UP(gso_skb->len - sizeof(*uh),

From: Willem de Bruijn willemb@google.com

mainline inclusion from mainline-v6.11 commit 6513eb3d3191574b58859ef2d6dc26c0277c6f81 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IAKQ33 CVE: CVE-2024-43817

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...

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The referenced commit drops bad input, but has false positives. Tighten the check to avoid these.

The check detects illegal checksum offload requests, which produce csum_start/csum_off beyond end of packet after segmentation.

But it is based on two incorrect assumptions:

1. virtio_net_hdr_to_skb with VIRTIO_NET_HDR_GSO_TCP[46] implies GSO. True in callers that inject into the tx path, such as tap. But false in callers that inject into rx, like virtio-net. Here, the flags indicate GRO, and CHECKSUM_UNNECESSARY or CHECKSUM_NONE without VIRTIO_NET_HDR_F_NEEDS_CSUM is normal.

2. TSO requires checksum offload, i.e., ip_summed == CHECKSUM_PARTIAL. False, as tcp[46]_gso_segment will fix up csum_start and offset for all other ip_summed by calling __tcp_v4_send_check.

Because of 2, we can limit the scope of the fix to virtio_net_hdr that do try to set these fields, with a bogus value.

Link: https://lore.kernel.org/netdev/20240909094527.GA3048202@port70.net/ Fixes: 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr") Signed-off-by: Willem de Bruijn willemb@google.com Acked-by: Jason Wang jasowang@redhat.com Acked-by: Michael S. Tsirkin mst@redhat.com Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20240910213553.839926-1-willemdebruijn.kernel@gmail... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Zhang Changzhong zhangchangzhong@huawei.com --- include/linux/virtio_net.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index c72e781..8bb04b4 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -151,7 +151,8 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, break; case SKB_GSO_TCPV4: case SKB_GSO_TCPV6: - if (skb->csum_offset != offsetof(struct tcphdr, check)) + if (skb->ip_summed == CHECKSUM_PARTIAL && + skb->csum_offset != offsetof(struct tcphdr, check)) return -EINVAL; break; }