On 03/14/2018 04:30 PM, syzbot wrote: > syzbot has found reproducer for the following crash on net-next commit > a870a02cc963de35452bbed932560ed69725c4f2 (Tue Mar 13 20:58:39 2018 +0000) > pktgen: use dynamic allocation for debug print buffer > > So far this crash happened 7 times on mmots, net-next. > C reproducer is attached. > syzkaller reproducer is attached. > Raw console output is attached. > compiler: gcc (GCC) 7.1.1 20170620 > .config is attached. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+ed43b6903ab968b16...@syzkaller.appspotmail.com > It will help syzbot understand when the bug is fixed. > > ================================================================== > BUG: KASAN: use-after-free in qdisc_pkt_len include/net/sch_generic.h:610 > [inline] > BUG: KASAN: use-after-free in qdisc_qstats_cpu_backlog_inc > include/net/sch_generic.h:712 [inline] > BUG: KASAN: use-after-free in pfifo_fast_enqueue+0x4bc/0x5e0 > net/sched/sch_generic.c:639 > Read of size 4 at addr ffff8801cede37e8 by task syzkaller717588/5543 > > CPU: 1 PID: 5543 Comm: syzkaller717588 Not tainted 4.16.0-rc4+ #265 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS > Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:17 [inline] > dump_stack+0x194/0x24d lib/dump_stack.c:53 > print_address_description+0x73/0x250 mm/kasan/report.c:256 > kasan_report_error mm/kasan/report.c:354 [inline] > kasan_report+0x23c/0x360 mm/kasan/report.c:412 > __asan_report_load4_noabort+0x14/0x20 mm/kasan/report.c:432 > qdisc_pkt_len include/net/sch_generic.h:610 [inline] > qdisc_qstats_cpu_backlog_inc include/net/sch_generic.h:712 [inline] > pfifo_fast_enqueue+0x4bc/0x5e0 net/sched/sch_generic.c:639 > __dev_xmit_skb net/core/dev.c:3216 [inline] > __dev_queue_xmit+0xd50/0x2f30 net/core/dev.c:3517 > dev_queue_xmit+0x17/0x20 net/core/dev.c:3582 > neigh_hh_output include/net/neighbour.h:472 [inline] > neigh_output include/net/neighbour.h:480 [inline] > ip6_finish_output2+0x1472/0x23d0 net/ipv6/ip6_output.c:120 > ip6_finish_output+0x69b/0xaf0 net/ipv6/ip6_output.c:154 > NF_HOOK_COND include/linux/netfilter.h:277 [inline] > ip6_output+0x1eb/0x840 net/ipv6/ip6_output.c:171 > dst_output include/net/dst.h:444 [inline] > ip6_local_out+0x95/0x160 net/ipv6/output_core.c:176 > ip6_send_skb+0xa1/0x330 net/ipv6/ip6_output.c:1677 > ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1697 > rawv6_push_pending_frames net/ipv6/raw.c:616 [inline] > rawv6_sendmsg+0x2f96/0x40c0 net/ipv6/raw.c:935 > inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763 > sock_sendmsg_nosec net/socket.c:629 [inline] > sock_sendmsg+0xca/0x110 net/socket.c:639 > ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047 > __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137 > SYSC_sendmmsg net/socket.c:2168 [inline] > SyS_sendmmsg+0x35/0x60 net/socket.c:2163 > do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > RIP: 0033:0x447739 > RSP: 002b:00007fb444290d58 EFLAGS: 00000297 ORIG_RAX: 0000000000000133 > RAX: ffffffffffffffda RBX: 00000000006f0084 RCX: 0000000000447739 > RDX: 0000000000000249 RSI: 0000000020001300 RDI: 0000000000000353 > RBP: 0000000000000000 R08: 0000000020000000 R09: 0000000020000000 > R10: 0000000000000000 R11: 0000000000000297 R12: 00000000006f0080 > R13: 00000000007ffd8f R14: 00007fb4442919c0 R15: 000000000000000a > > Allocated by task 5543: > save_stack+0x43/0xd0 mm/kasan/kasan.c:447 > set_track mm/kasan/kasan.c:459 [inline] > kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:552 > kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:489 > kmem_cache_alloc_node+0x144/0x760 mm/slab.c:3631 > __alloc_skb+0xf1/0x780 net/core/skbuff.c:193 > alloc_skb include/linux/skbuff.h:986 [inline] > sock_wmalloc+0x140/0x1d0 net/core/sock.c:1942 > __ip6_append_data.isra.43+0x26b9/0x3390 net/ipv6/ip6_output.c:1416 > ip6_append_data+0x189/0x290 net/ipv6/ip6_output.c:1571 > rawv6_sendmsg+0x1e09/0x40c0 net/ipv6/raw.c:928 > inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763 > sock_sendmsg_nosec net/socket.c:629 [inline] > sock_sendmsg+0xca/0x110 net/socket.c:639 > ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047 > __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137 > SYSC_sendmmsg net/socket.c:2168 [inline] > SyS_sendmmsg+0x35/0x60 net/socket.c:2163 > do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > > Freed by task 5531: > save_stack+0x43/0xd0 mm/kasan/kasan.c:447 > set_track mm/kasan/kasan.c:459 [inline] > __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:520 > kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:527 > __cache_free mm/slab.c:3485 [inline] > kmem_cache_free+0x83/0x2a0 mm/slab.c:3743 > kfree_skbmem+0x1a1/0x1d0 net/core/skbuff.c:582 > __kfree_skb net/core/skbuff.c:642 [inline] > kfree_skb+0x165/0x4c0 net/core/skbuff.c:659 > ip_tunnel_xmit+0x710/0x3550 net/ipv4/ip_tunnel.c:778 > __gre_xmit+0x546/0x8b0 net/ipv4/ip_gre.c:449 > erspan_xmit+0x779/0x22a0 net/ipv4/ip_gre.c:731 > __netdev_start_xmit include/linux/netdevice.h:4078 [inline] > netdev_start_xmit include/linux/netdevice.h:4087 [inline] > xmit_one net/core/dev.c:3026 [inline] > dev_hard_start_xmit+0x24e/0xac0 net/core/dev.c:3042 > sch_direct_xmit+0x40d/0x1140 net/sched/sch_generic.c:327 > qdisc_restart net/sched/sch_generic.c:393 [inline] > __qdisc_run+0x57d/0x19c0 net/sched/sch_generic.c:401 > __dev_xmit_skb net/core/dev.c:3217 [inline] > __dev_queue_xmit+0xd5e/0x2f30 net/core/dev.c:3517 > dev_queue_xmit+0x17/0x20 net/core/dev.c:3582 > neigh_hh_output include/net/neighbour.h:472 [inline] > neigh_output include/net/neighbour.h:480 [inline] > ip6_finish_output2+0x1472/0x23d0 net/ipv6/ip6_output.c:120 > ip6_finish_output+0x69b/0xaf0 net/ipv6/ip6_output.c:154 > NF_HOOK_COND include/linux/netfilter.h:277 [inline] > ip6_output+0x1eb/0x840 net/ipv6/ip6_output.c:171 > dst_output include/net/dst.h:444 [inline] > ip6_local_out+0x95/0x160 net/ipv6/output_core.c:176 > ip6_send_skb+0xa1/0x330 net/ipv6/ip6_output.c:1677 > ip6_push_pending_frames+0xb3/0xe0 net/ipv6/ip6_output.c:1697 > rawv6_push_pending_frames net/ipv6/raw.c:616 [inline] > rawv6_sendmsg+0x2f96/0x40c0 net/ipv6/raw.c:935 > inet_sendmsg+0x11f/0x5e0 net/ipv4/af_inet.c:763 > sock_sendmsg_nosec net/socket.c:629 [inline] > sock_sendmsg+0xca/0x110 net/socket.c:639 > ___sys_sendmsg+0x320/0x8b0 net/socket.c:2047 > __sys_sendmmsg+0x1ee/0x620 net/socket.c:2137 > SYSC_sendmmsg net/socket.c:2168 [inline] > SyS_sendmmsg+0x35/0x60 net/socket.c:2163 > do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 > entry_SYSCALL_64_after_hwframe+0x42/0xb7 > > The buggy address belongs to the object at ffff8801cede37c0 > which belongs to the cache skbuff_head_cache of size 232 > The buggy address is located 40 bytes inside of > 232-byte region [ffff8801cede37c0, ffff8801cede38a8) > The buggy address belongs to the page: > page:ffffea00073b78c0 count:1 mapcount:0 mapping:ffff8801cede3040 index:0x0 > flags: 0x2fffc0000000100(slab) > raw: 02fffc0000000100 ffff8801cede3040 0000000000000000 000000010000000c > raw: ffffea00074946a0 ffffea00074c6d60 ffff8801d940fcc0 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff8801cede3680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8801cede3700: fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc fc >> ffff8801cede3780: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb > ^ > ffff8801cede3800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff8801cede3880: fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc > ================================================================== >
typical use after free... diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 190570f21b208d5a17943360a3a6f85e1c2a2187..663e016491773f40f81d9bbfeab3dd68e1c2fc5c 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -628,6 +628,7 @@ static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc, int band = prio2band[skb->priority & TC_PRIO_MAX]; struct pfifo_fast_priv *priv = qdisc_priv(qdisc); struct skb_array *q = band2list(priv, band); + unsigned int pkt_len = qdisc_pkt_len(skb); int err; err = skb_array_produce(q, skb); @@ -636,7 +637,7 @@ static int pfifo_fast_enqueue(struct sk_buff *skb, struct Qdisc *qdisc, return qdisc_drop_cpu(skb, qdisc, to_free); qdisc_qstats_cpu_qlen_inc(qdisc); - qdisc_qstats_cpu_backlog_inc(qdisc, skb); + this_cpu_add(qdisc->cpu_qstats->backlog, pkt_len); return NET_XMIT_SUCCESS; }