🛡️ CVE-2024-50045 — kernel

netfilter: br_netfilter: fix panic with metadata_dst skb

In the Linux kernel, the following vulnerability has been resolved:

netfilter: br_netfilter: fix panic with metadata_dst skb

Fix a kernel panic in the br_netfilter module when sending untagged

traffic via a VxLAN device.

This happens during the check for fragmentation in br_nf_dev_queue_xmit.

It is dependent on:

1) the br_netfilter module being loaded;

2) net.bridge.bridge-nf-call-iptables set to 1;

3) a bridge with a VxLAN (single-vxlan-device) netdevice as a bridge port;

4) untagged frames with size higher than the VxLAN MTU forwarded/flooded

When forwarding the untagged packet to the VxLAN bridge port, before

the netfilter hooks are called, br_handle_egress_vlan_tunnel is called and

changes the skb_dst to the tunnel dst. The tunnel_dst is a metadata type

of dst, i.e., skb_valid_dst(skb) is false, and metadata->dst.dev is NULL.

Then in the br_netfilter hooks, in br_nf_dev_queue_xmit, there's a check

for frames that needs to be fragmented: frames with higher MTU than the

VxLAN device end up calling br_nf_ip_fragment, which in turns call

ip_skb_dst_mtu.

The ip_dst_mtu tries to use the skb_dst(skb) as if it was a valid dst

with valid dst->dev, thus the crash.

This case was never supported in the first place, so drop the packet

instead.

PING 10.0.0.2 (10.0.0.2) from 0.0.0.0 h1-eth0: 2000(2028) bytes of data.

[ 176.291791] Unable to handle kernel NULL pointer dereference at

virtual address 0000000000000110

[ 176.292101] Mem abort info:

[ 176.292184] ESR = 0x0000000096000004

[ 176.292322] EC = 0x25: DABT (current EL), IL = 32 bits

[ 176.292530] SET = 0, FnV = 0

[ 176.292709] EA = 0, S1PTW = 0

[ 176.292862] FSC = 0x04: level 0 translation fault

[ 176.293013] Data abort info:

[ 176.293104] ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000

[ 176.293488] CM = 0, WnR = 0, TnD = 0, TagAccess = 0

[ 176.293787] GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0

[ 176.293995] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000043ef5000

[ 176.294166] [0000000000000110] pgd=0000000000000000,

p4d=0000000000000000

[ 176.294827] Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP

[ 176.295252] Modules linked in: vxlan ip6_udp_tunnel udp_tunnel veth

br_netfilter bridge stp llc ipv6 crct10dif_ce

[ 176.295923] CPU: 0 PID: 188 Comm: ping Not tainted

6.8.0-rc3-g5b3fbd61b9d1 #2

[ 176.296314] Hardware name: linux,dummy-virt (DT)

[ 176.296535] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS

BTYPE=--)

[ 176.296808] pc : br_nf_dev_queue_xmit+0x390/0x4ec [br_netfilter]

[ 176.297382] lr : br_nf_dev_queue_xmit+0x2ac/0x4ec [br_netfilter]

[ 176.297636] sp : ffff800080003630

[ 176.297743] x29: ffff800080003630 x28: 0000000000000008 x27:

ffff6828c49ad9f8

[ 176.298093] x26: ffff6828c49ad000 x25: 0000000000000000 x24:

00000000000003e8

[ 176.298430] x23: 0000000000000000 x22: ffff6828c4960b40 x21:

ffff6828c3b16d28

[ 176.298652] x20: ffff6828c3167048 x19: ffff6828c3b16d00 x18:

0000000000000014

[ 176.298926] x17: ffffb0476322f000 x16: ffffb7e164023730 x15:

0000000095744632

[ 176.299296] x14: ffff6828c3f1c880 x13: 0000000000000002 x12:

ffffb7e137926a70

[ 176.299574] x11: 0000000000000001 x10: ffff6828c3f1c898 x9 :

0000000000000000

[ 176.300049] x8 : ffff6828c49bf070 x7 : 0008460f18d5f20e x6 :

f20e0100bebafeca

[ 176.300302] x5 : ffff6828c7f918fe x4 : ffff6828c49bf070 x3 :

0000000000000000

[ 176.300586] x2 : 0000000000000000 x1 : ffff6828c3c7ad00 x0 :

ffff6828c7f918f0

[ 176.300889] Call trace:

[ 176.301123] br_nf_dev_queue_xmit+0x390/0x4ec [br_netfilter]

[ 176.301411] br_nf_post_routing+0x2a8/0x3e4 [br_netfilter]

[ 176.301703] nf_hook_slow+0x48/0x124

[ 176.302060] br_forward_finish+0xc8/0xe8 [bridge]

[ 176.302371] br_nf_hook_thresh+0x124/0x134 [br_netfilter]

[ 176.302605] br_nf_forward_finish+0x118/0x22c [br_netfilter]

[ 176.302824] br_nf_forward_ip.part.0+0x264/0x290 [br_netfilter]

[ 176.303136] br_nf_forward+0x2b8/0x4e0 [br_netfilter]

[ 176.303359] nf_hook_slow+0x48/0x124

[ 176.303

---truncated---