CVE-2024-40957

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

seg6: fix parameter passing when calling NF_HOOK() in End.DX4 and End.DX6 behaviors

input_action_end_dx4() and input_action_end_dx6() are called NF_HOOK() for PREROUTING hook, in PREROUTING hook, we should passing a valid indev, and a NULL outdev to NF_HOOK(), otherwise may trigger a NULL pointer dereference, as below:

[74830.647293] BUG: kernel NULL pointer dereference, address: 0000000000000090
[74830.655633] #PF: supervisor read access in kernel mode
[74830.657888] #PF: error_code(0x0000) - not-present page
[74830.659500] PGD 0 P4D 0
[74830.660450] Oops: 0000 [#1] PREEMPT SMP PTI
...
[74830.664953] Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
[74830.666569] RIP: 0010:rpfilter_mt+0x44/0x15e [ipt_rpfilter]
...
[74830.689725] Call Trace:
[74830.690402]  <IRQ>
[74830.690953]  ? show_trace_log_lvl+0x1c4/0x2df
[74830.692020]  ? show_trace_log_lvl+0x1c4/0x2df
[74830.693095]  ? ipt_do_table+0x286/0x710 [ip_tables]
[74830.694275]  ? __die_body.cold+0x8/0xd
[74830.695205]  ? page_fault_oops+0xac/0x140
[74830.696244]  ? exc_page_fault+0x62/0x150
[74830.697225]  ? asm_exc_page_fault+0x22/0x30
[74830.698344]  ? rpfilter_mt+0x44/0x15e [ipt_rpfilter]
[74830.699540]  ipt_do_table+0x286/0x710 [ip_tables]
[74830.700758]  ? ip6_route_input+0x19d/0x240
[74830.701752]  nf_hook_slow+0x3f/0xb0
[74830.702678]  input_action_end_dx4+0x19b/0x1e0
[74830.703735]  ? input_action_end_t+0xe0/0xe0
[74830.704734]  seg6_local_input_core+0x2d/0x60
[74830.705782]  lwtunnel_input+0x5b/0xb0
[74830.706690]  __netif_receive_skb_one_core+0x63/0xa0
[74830.707825]  process_backlog+0x99/0x140
[74830.709538]  __napi_poll+0x2c/0x160
[74830.710673]  net_rx_action+0x296/0x350
[74830.711860]  __do_softirq+0xcb/0x2ac
[74830.713049]  do_softirq+0x63/0x90

input_action_end_dx4() passing a NULL indev to NF_HOOK(), and finally trigger a NULL dereference in rpfilter_mt()->rpfilter_is_loopback():

static bool
rpfilter_is_loopback(const struct sk_buff *skb,
      	       const struct net_device *in)
{
        // in is NULL
        return skb->pkt_type == PACKET_LOOPBACK ||
      	 in->flags & IFF_LOOPBACK;
}

Weakness

A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/561475d53aa7e4511ee7cdba8728ded81cf1db1c
• https://git.kernel.org/stable/c/9a3bc8d16e0aacd65c31aaf23a2bced3288a7779
• https://git.kernel.org/stable/c/af90e3d73dc45778767b2fb6e7edd57ebe34380d
• https://git.kernel.org/stable/c/d62df86c172033679d744f07d89e93e367dd11f6
• https://git.kernel.org/stable/c/ec4d970b597ee5e17b0d8d73b7875197ce9a04d4