Re: af_packet: use after free in prb_retire_rx_blk_timer_expired

From: Cong Wang
Date: Sat Jul 22 2017 - 15:02:29 EST


Hello,

On Sat, Jul 22, 2017 at 2:55 AM, liujian (CE) <liujian56@xxxxxxxxxx> wrote:
> I also hit this issue with trinity test:
>
> The call trace:
> [exception RIP: prb_retire_rx_blk_timer_expired+70]
> RIP: ffffffff81633be6 RSP: ffff8801bec03dc0 RFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffff8801b49d0948 RCX: 0000000000000000
> RDX: ffff8801b31057a0 RSI: a56b6b6b6b6b6b6b RDI: ffff8801b49d09ec
> RBP: ffff8801bec03dd8 R8: 0000000000000001 R9: ffffffff83e1bf80
> R10: 0000000000000002 R11: 0000000000000005 R12: ffff8801b49d09ec
> R13: 0000000000000100 R14: ffffffff81633ba0 R15: ffff8801b49d0948
> ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
> #7 [ffff8801bec03de0] call_timer_fn at ffffffff8108cb76
> #8 [ffff8801bec03e18] run_timer_softirq at ffffffff8108f87c
> #9 [ffff8801bec03e90] __do_softirq at ffffffff8108629f
> #10 [ffff8801bec03f00] call_softirq at ffffffff8166a01c
> #11 [ffff8801bec03f18] do_softirq at ffffffff810172ad
> #12 [ffff8801bec03f30] irq_exit at ffffffff81086655
> #13 [ffff8801bec03f48] msa_irq_exit at ffffffff810b1ab3
> #14 [ffff8801bec03f88] smp_apic_timer_interrupt at ffffffff8166aeae
> #15 [ffff8801bec03fb0] apic_timer_interrupt at ffffffff816692dd
> --- <IRQ stack> ---
>
> And from vmcore, I can see the pointer GET_CURR_PBLOCK_DESC_FROM_CORE(pkc); is a56b6b6b6b6b6b6b
>

Does the following quick fix help?


diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 008bb34ee324..09ec1640e5f7 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -4264,6 +4264,7 @@ static int packet_set_ring(struct sock *sk,
union tpacket_req_u *req_u,
/* Block transmit is not supported yet */
if (!tx_ring) {
init_prb_bdqc(po, rb, pg_vec, req_u);
+ pg_vec = NULL;
} else {
struct tpacket_req3 *req3 = &req_u->req3;