From c800aaf8d869f2b9b47b10c5c312fe19f0a94042 Mon Sep 17 00:00:00 2001 From: WANG Cong Date: Mon, 24 Jul 2017 10:07:32 -0700 Subject: [PATCH] packet: fix use-after-free in prb_retire_rx_blk_timer_expired() There are multiple reports showing we have a use-after-free in the timer prb_retire_rx_blk_timer_expired(), where we use struct tpacket_kbdq_core::pkbdq, a pg_vec, after it gets freed by free_pg_vec(). The interesting part is it is not freed via packet_release() but via packet_setsockopt(), which means we are not closing the socket. Looking into the big and fat function packet_set_ring(), this could happen if we satisfy the following conditions: 1. closing == 0, not on packet_release() path 2. req->tp_block_nr == 0, we don't allocate a new pg_vec 3. rx_ring->pg_vec is already set as V3, which means we already called packet_set_ring() wtih req->tp_block_nr > 0 previously 4. req->tp_frame_nr == 0, pass sanity check 5. po->mapped == 0, never called mmap() In this scenario we are clearing the old rx_ring->pg_vec, so we need to free this pg_vec, but we don't stop the timer on this path because of closing==0. The timer has to be stopped as long as we need to free pg_vec, therefore the check on closing!=0 is wrong, we should check pg_vec!=NULL instead. Thanks to liujian for testing different fixes. Reported-by: alexander.levin@verizon.com Reported-by: Dave Jones Reported-by: liujian (CE) Tested-by: liujian (CE) Cc: Ding Tianhong Cc: Willem de Bruijn Signed-off-by: Cong Wang Signed-off-by: David S. Miller --- net/packet/af_packet.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 008bb34ee324..0615c2a950fa 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -4329,7 +4329,7 @@ static int packet_set_ring(struct sock *sk, union tpacket_req_u *req_u, register_prot_hook(sk); } spin_unlock(&po->bind_lock); - if (closing && (po->tp_version > TPACKET_V2)) { + if (pg_vec && (po->tp_version > TPACKET_V2)) { /* Because we don't support block-based V3 on tx-ring */ if (!tx_ring) prb_shutdown_retire_blk_timer(po, rb_queue); -- GitLab