Date:   Fri, 18 May 2018 09:05:23 -0400
From:   Craig Gallek <kraig@...gle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net] sock_diag: fix use-after-free read in __sk_free

On Fri, May 18, 2018 at 7:47 AM, Eric Dumazet <edumazet@...gle.com> wrote:
> We must not call sock_diag_has_destroy_listeners(sk) on a socket
> that has no reference on net structure.
>
> BUG: KASAN: use-after-free in sock_diag_has_destroy_listeners include/linux/sock_diag.h:75 [inline]
> BUG: KASAN: use-after-free in __sk_free+0x329/0x340 net/core/sock.c:1609
> Read of size 8 at addr ffff88018a02e3a0 by task swapper/1/0
>
> CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.17.0-rc5+ #54
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1b9/0x294 lib/dump_stack.c:113
>  print_address_description+0x6c/0x20b mm/kasan/report.c:256
>  kasan_report_error mm/kasan/report.c:354 [inline]
>  kasan_report.cold.7+0x242/0x2fe mm/kasan/report.c:412
>  __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:433
>  sock_diag_has_destroy_listeners include/linux/sock_diag.h:75 [inline]
>  __sk_free+0x329/0x340 net/core/sock.c:1609
>  sk_free+0x42/0x50 net/core/sock.c:1623
>  sock_put include/net/sock.h:1664 [inline]
>  reqsk_free include/net/request_sock.h:116 [inline]
>  reqsk_put include/net/request_sock.h:124 [inline]
>  inet_csk_reqsk_queue_drop_and_put net/ipv4/inet_connection_sock.c:672 [inline]
>  reqsk_timer_handler+0xe27/0x10e0 net/ipv4/inet_connection_sock.c:739
>  call_timer_fn+0x230/0x940 kernel/time/timer.c:1326
>  expire_timers kernel/time/timer.c:1363 [inline]
>  __run_timers+0x79e/0xc50 kernel/time/timer.c:1666
>  run_timer_softirq+0x4c/0x70 kernel/time/timer.c:1692
>  __do_softirq+0x2e0/0xaf5 kernel/softirq.c:285
>  invoke_softirq kernel/softirq.c:365 [inline]
>  irq_exit+0x1d1/0x200 kernel/softirq.c:405
>  exiting_irq arch/x86/include/asm/apic.h:525 [inline]
>  smp_apic_timer_interrupt+0x17e/0x710 arch/x86/kernel/apic/apic.c:1052
>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:863
>  </IRQ>
> RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54
> RSP: 0018:ffff8801d9ae7c38 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff13
> RAX: dffffc0000000000 RBX: 1ffff1003b35cf8a RCX: 0000000000000000
> RDX: 1ffffffff11a30d0 RSI: 0000000000000001 RDI: ffffffff88d18680
> RBP: ffff8801d9ae7c38 R08: ffffed003b5e46c3 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
> R13: ffff8801d9ae7cf0 R14: ffffffff897bef20 R15: 0000000000000000
>  arch_safe_halt arch/x86/include/asm/paravirt.h:94 [inline]
>  default_idle+0xc2/0x440 arch/x86/kernel/process.c:354
>  arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:345
>  default_idle_call+0x6d/0x90 kernel/sched/idle.c:93
>  cpuidle_idle_call kernel/sched/idle.c:153 [inline]
>  do_idle+0x395/0x560 kernel/sched/idle.c:262
>  cpu_startup_entry+0x104/0x120 kernel/sched/idle.c:368
>  start_secondary+0x426/0x5b0 arch/x86/kernel/smpboot.c:269
>  secondary_startup_64+0xa5/0xb0 arch/x86/kernel/head_64.S:242
>
> Allocated by task 4557:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  kasan_kmalloc+0xc4/0xe0 mm/kasan/kasan.c:553
>  kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:490
>  kmem_cache_alloc+0x12e/0x760 mm/slab.c:3554
>  kmem_cache_zalloc include/linux/slab.h:691 [inline]
>  net_alloc net/core/net_namespace.c:383 [inline]
>  copy_net_ns+0x159/0x4c0 net/core/net_namespace.c:423
>  create_new_namespaces+0x69d/0x8f0 kernel/nsproxy.c:107
>  unshare_nsproxy_namespaces+0xc3/0x1f0 kernel/nsproxy.c:206
>  ksys_unshare+0x708/0xf90 kernel/fork.c:2408
>  __do_sys_unshare kernel/fork.c:2476 [inline]
>  __se_sys_unshare kernel/fork.c:2474 [inline]
>  __x64_sys_unshare+0x31/0x40 kernel/fork.c:2474
>  do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Freed by task 69:
>  save_stack+0x43/0xd0 mm/kasan/kasan.c:448
>  set_track mm/kasan/kasan.c:460 [inline]
>  __kasan_slab_free+0x11a/0x170 mm/kasan/kasan.c:521
>  kasan_slab_free+0xe/0x10 mm/kasan/kasan.c:528
>  __cache_free mm/slab.c:3498 [inline]
>  kmem_cache_free+0x86/0x2d0 mm/slab.c:3756
>  net_free net/core/net_namespace.c:399 [inline]
>  net_drop_ns.part.14+0x11a/0x130 net/core/net_namespace.c:406
>  net_drop_ns net/core/net_namespace.c:405 [inline]
>  cleanup_net+0x6a1/0xb20 net/core/net_namespace.c:541
>  process_one_work+0xc1e/0x1b50 kernel/workqueue.c:2145
>  worker_thread+0x1cc/0x1440 kernel/workqueue.c:2279
>  kthread+0x345/0x410 kernel/kthread.c:240
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:412
>
> The buggy address belongs to the object at ffff88018a02c140
>  which belongs to the cache net_namespace of size 8832
> The buggy address is located 8800 bytes inside of
>  8832-byte region [ffff88018a02c140, ffff88018a02e3c0)
> The buggy address belongs to the page:
> page:ffffea0006280b00 count:1 mapcount:0 mapping:ffff88018a02c140 index:0x0 compound_mapcount: 0
> flags: 0x2fffc0000008100(slab|head)
> raw: 02fffc0000008100 ffff88018a02c140 0000000000000000 0000000100000001
> raw: ffffea00062a1320 ffffea0006268020 ffff8801d9bdde40 0000000000000000
> page dumped because: kasan: bad access detected
>
> Fixes: b922622ec6ef ("sock_diag: don't broadcast kernel sockets")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Cc: Craig Gallek <kraig@...gle.com>
> Reported-by: syzbot <syzkaller@...glegroups.com>

Acked-by: Craig Gallek <kraig@...gle.com>

Thanks Eric!

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