CVE-2025-21720: In the Linux kernel, the following vulnerability has been resolved:  xfrm: delete intermediate secpath entry in packet offload mode  Packets handled by hardware have added secpath as a way to inform XFRM core code that this path was already handled. That secpath is not needed at all after policy is checked and it is removed later in the stack.  However, in the case of IP forwarding is enabled (/proc/sys/net/ipv4/ip_forward), that secpath is not removed and packets which already were handled are reentered to the driver TX path with xfrm_offload set.  The following kernel panic is observed in mlx5 in such case:   mlx5_core 0000:04:00.0 enp4s0f0np0: Link up  mlx5_core 0000:04:00.1 enp4s0f1np1: Link up  Initializing XFRM netlink socket  IPsec XFRM device driver  BUG: kernel NULL pointer dereference, address: 0000000000000000  #PF: supervisor instruction fetch in kernel mode  #PF: error_code(0x0010) - not-present page  PGD 0 P4D 0  Oops: Oops: 0010 [#1] PREEMPT SMP  CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted 6.13.0-rc1-alex #3  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1.1 04/01/2014  RIP: 0010:0x0  Code: Unable to access opcode bytes at 0xffffffffffffffd6.  RSP: 0018:ffffb87380003800 EFLAGS: 00010206  RAX: ffff8df004e02600 RBX: ffffb873800038d8 RCX: 00000000ffff98cf  RDX: ffff8df00733e108 RSI: ffff8df00521fb80 RDI: ffff8df001661f00  RBP: ffffb87380003850 R08: ffff8df013980000 R09: 0000000000000010  R10: 0000000000000002 R11: 0000000000000002 R12: ffff8df001661f00  R13: ffff8df00521fb80 R14: ffff8df00733e108 R15: ffff8df011faf04e  FS:  0000000000000000(0000) GS:ffff8df46b800000(0000) knlGS:0000000000000000  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033  CR2: ffffffffffffffd6 CR3: 0000000106384000 CR4: 0000000000350ef0  Call Trace:   <IRQ>   ? show_regs+0x63/0x70   ? __die_body+0x20/0x60   ? __die+0x2b/0x40   ? page_fault_oops+0x15c/0x550   ? do_user_addr_fault+0x3ed/0x870   ? exc_page_fault+0x7f/0x190   ? asm_exc_page_fault+0x27/0x30   mlx5e_ipsec_handle_tx_skb+0xe7/0x2f0 [mlx5_core]   mlx5e_xmit+0x58e/0x1980 [mlx5_core]   ? __fib_lookup+0x6a/0xb0   dev_hard_start_xmit+0x82/0x1d0   sch_direct_xmit+0xfe/0x390   __dev_queue_xmit+0x6d8/0xee0   ? __fib_lookup+0x6a/0xb0   ? internal_add_timer+0x48/0x70   ? mod_timer+0xe2/0x2b0   neigh_resolve_output+0x115/0x1b0   __neigh_update+0x26a/0xc50   neigh_update+0x14/0x20   arp_process+0x2cb/0x8e0   ? __napi_build_skb+0x5e/0x70   arp_rcv+0x11e/0x1c0   ? dev_gro_receive+0x574/0x820   __netif_receive_skb_list_core+0x1cf/0x1f0   netif_receive_skb_list_internal+0x183/0x2a0   napi_complete_done+0x76/0x1c0   mlx5e_napi_poll+0x234/0x7a0 [mlx5_core]   __napi_poll+0x2d/0x1f0   net_rx_action+0x1a6/0x370   ? atomic_notifier_call_chain+0x3b/0x50   ? irq_int_handler+0x15/0x20 [mlx5_core]   handle_softirqs+0xb9/0x2f0   ? handle_irq_event+0x44/0x60   irq_exit_rcu+0xdb/0x100   common_interrupt+0x98/0xc0   </IRQ>   <TASK>   asm_common_interrupt+0x27/0x40  RIP: 0010:pv_native_safe_halt+0xb/0x10  Code: 09 c3 66 66 2e 0f 1f 84 00 00 00 00 00 66 90 0f 22  0f 1f 84 00 00 00 00 00 90 eb 07 0f 00 2d 7f e9 36 00 fb 40 00 83 ff 07 77 21 89 ff ff 24 fd 88 3d a1 bd 0f 21 f8  RSP: 0018:ffffffffbe603de8 EFLAGS: 00000202  RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000f92f46680  RDX: 0000000000000037 RSI: 00000000ffffffff RDI: 00000000000518d4  RBP: ffffffffbe603df0 R08: 000000cd42e4dffb R09: ffffffffbe603d70  R10: 0000004d80d62680 R11: 0000000000000001 R12: ffffffffbe60bf40  R13: 0000000000000000 R14: 0000000000000000 R15: ffffffffbe60aff8   ? default_idle+0x9/0x20   arch_cpu_idle+0x9/0x10   default_idle_call+0x29/0xf0   do_idle+0x1f2/0x240   cpu_startup_entry+0x2c/0x30   rest_init+0xe7/0x100   start_kernel+0x76b/0xb90   x86_64_start_reservations+0x18/0x30   x86_64_start_kernel+0xc0/0x110   ? setup_ghcb+0xe/0x130   common_startup_64+0x13e/0x141   </TASK>  Modules linked in: esp4_offload esp4 xfrm_interface xfrm6_tunnel tunnel4 tunnel6 xfrm_user xfrm_algo binf ---truncated---