3.9 KiB
CVE-2024-50154
Description
In the Linux kernel, the following vulnerability has been resolved:tcp/dccp: Don't use timer_pending() in reqsk_queue_unlink().Martin KaFai Lau reported use-after-free [0] in reqsk_timer_handler(). """ We are seeing a use-after-free from a bpf prog attached to trace_tcp_retransmit_synack. The program passes the req->sk to the bpf_sk_storage_get_tracing kernel helper which does check for null before using it. """The commit 83fccfc3940c ("inet: fix potential deadlock inreqsk_queue_unlink()") added timer_pending() in reqsk_queue_unlink() notto call del_timer_sync() from reqsk_timer_handler(), but it introduced asmall race window.Before the timer is called, expire_timers() calls detach_timer(timer, true)to clear timer->entry.pprev and marks it as not pending.If reqsk_queue_unlink() checks timer_pending() just after expire_timers()calls detach_timer(), TCP will miss del_timer_sync(); the reqsk timer willcontinue running and send multiple SYN+ACKs until it expires.The reported UAF could happen if req->sk is close()d earlier than the timerexpiration, which is 63s by default.The scenario would be 1. inet_csk_complete_hashdance() calls inet_csk_reqsk_queue_drop(), but del_timer_sync() is missed 2. reqsk timer is executed and scheduled again 3. req->sk is accept()ed and reqsk_put() decrements rsk_refcnt, but reqsk timer still has another one, and inet_csk_accept() does not clear req->sk for non-TFO sockets 4. sk is close()d 5. reqsk timer is executed again, and BPF touches req->skLet's not use timer_pending() by passing the caller context to__inet_csk_reqsk_queue_drop().Note that reqsk timer is pinned, so the issue does not happen in mostuse cases. [1][0]BUG: KFENCE: use-after-free read in bpf_sk_storage_get_tracing+0x2e/0x1b0Use-after-free read at 0x00000000a891fb3a (in kfence-#1):bpf_sk_storage_get_tracing+0x2e/0x1b0bpf_prog_5ea3e95db6da0438_tcp_retransmit_synack+0x1d20/0x1ddabpf_trace_run2+0x4c/0xc0tcp_rtx_synack+0xf9/0x100reqsk_timer_handler+0xda/0x3d0run_timer_softirq+0x292/0x8a0irq_exit_rcu+0xf5/0x320sysvec_apic_timer_interrupt+0x6d/0x80asm_sysvec_apic_timer_interrupt+0x16/0x20intel_idle_irq+0x5a/0xa0cpuidle_enter_state+0x94/0x273cpu_startup_entry+0x15e/0x260start_secondary+0x8a/0x90secondary_startup_64_no_verify+0xfa/0xfbkfence-#1: 0x00000000a72cc7b6-0x00000000d97616d9, size=2376, cache=TCPv6allocated by task 0 on cpu 9 at 260507.901592s:sk_prot_alloc+0x35/0x140sk_clone_lock+0x1f/0x3f0inet_csk_clone_lock+0x15/0x160tcp_create_openreq_child+0x1f/0x410tcp_v6_syn_recv_sock+0x1da/0x700tcp_check_req+0x1fb/0x510tcp_v6_rcv+0x98b/0x1420ipv6_list_rcv+0x2258/0x26e0napi_complete_done+0x5b1/0x2990mlx5e_napi_poll+0x2ae/0x8d0net_rx_action+0x13e/0x590irq_exit_rcu+0xf5/0x320common_interrupt+0x80/0x90asm_common_interrupt+0x22/0x40cpuidle_enter_state+0xfb/0x273cpu_startup_entry+0x15e/0x260start_secondary+0x8a/0x90secondary_startup_64_no_verify+0xfa/0xfbfreed by task 0 on cpu 9 at 260507.927527s:rcu_core_si+0x4ff/0xf10irq_exit_rcu+0xf5/0x320sysvec_apic_timer_interrupt+0x6d/0x80asm_sysvec_apic_timer_interrupt+0x16/0x20cpuidle_enter_state+0xfb/0x273cpu_startup_entry+0x15e/0x260start_secondary+0x8a/0x90secondary_startup_64_no_verify+0xfa/0xfb
POC
Reference
No PoCs from references.