Re: net/ipv4: use-after-free in add_grec

From: Eric Dumazet
Date: Wed May 31 2017 - 12:12:42 EST

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On Wed, 2017-05-31 at 11:46 +0200, Andrey Konovalov wrote:
> Hi,
>
> I've got the following error report while fuzzing the kernel with syzkaller.
>
> On commit 5ed02dbb497422bf225783f46e6eadd237d23d6b (4.12-rc3).
>
> Unfortunately it's not reproducible.
>
> ==================================================================
> BUG: KASAN: use-after-free in add_grec+0x101e/0x1090 net/ipv4/igmp.c:473
> Read of size 8 at addr ffff88003053c1a0 by task swapper/0/0
>
> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.12.0-rc3+ #370
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
> Call Trace:
> <IRQ>
> __dump_stack lib/dump_stack.c:16 [inline]
> dump_stack+0x292/0x395 lib/dump_stack.c:52
> print_address_description+0x73/0x280 mm/kasan/report.c:252
> kasan_report_error mm/kasan/report.c:351 [inline]
> kasan_report+0x22b/0x340 mm/kasan/report.c:408
> __asan_report_load8_noabort+0x14/0x20 mm/kasan/report.c:429
> add_grec+0x101e/0x1090 net/ipv4/igmp.c:473
> igmpv3_send_cr net/ipv4/igmp.c:663 [inline]
> igmp_ifc_timer_expire+0x46d/0xa80 net/ipv4/igmp.c:768
> IPVS: length: 51 != 8
> call_timer_fn+0x23f/0x800 kernel/time/timer.c:1268
> expire_timers kernel/time/timer.c:1307 [inline]
> __run_timers+0x94e/0xcd0 kernel/time/timer.c:1601
> run_timer_softirq+0x21/0x80 kernel/time/timer.c:1614
> __do_softirq+0x2fb/0xb99 kernel/softirq.c:284
> invoke_softirq kernel/softirq.c:364 [inline]
> irq_exit+0x19e/0x1d0 kernel/softirq.c:405
> exiting_irq arch/x86/include/asm/apic.h:652 [inline]
> smp_apic_timer_interrupt+0x76/0xa0 arch/x86/kernel/apic/apic.c:966
> apic_timer_interrupt+0x93/0xa0 arch/x86/entry/entry_64.S:481
> RIP: 0010:native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
> RSP: 0018:ffffffff85a079a8 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff10
> RAX: dffffc0000000020 RBX: 1ffffffff0b40f38 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff85a2a9e4
> RBP: ffffffff85a079a8 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: dffffc0000000000
> R13: ffffffff85a07a60 R14: ffffffff86171338 R15: 1ffffffff0b40f5b
> </IRQ>
> arch_safe_halt arch/x86/include/asm/paravirt.h:98 [inline]
> default_idle+0x8f/0x440 arch/x86/kernel/process.c:341
> arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:332
> default_idle_call+0x36/0x60 kernel/sched/idle.c:98
> cpuidle_idle_call kernel/sched/idle.c:156 [inline]
> do_idle+0x348/0x420 kernel/sched/idle.c:245
> cpu_startup_entry+0x18/0x20 kernel/sched/idle.c:350
> rest_init+0x18d/0x1a0 init/main.c:415
> start_kernel+0x747/0x779 init/main.c:679
> x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:196
> x86_64_start_kernel+0x132/0x141 arch/x86/kernel/head64.c:177
> secondary_startup_64+0x9f/0x9f arch/x86/kernel/head_64.S:304
>
> Allocated by task 30543:
> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
> save_stack+0x43/0xd0 mm/kasan/kasan.c:513
> set_track mm/kasan/kasan.c:525 [inline]
> kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:617
> kmem_cache_alloc_trace+0x82/0x270 mm/slub.c:2745
> kmalloc include/linux/slab.h:492 [inline]
> kzalloc include/linux/slab.h:665 [inline]
> ip_mc_add1_src net/ipv4/igmp.c:1909 [inline]
> ip_mc_add_src+0x6cd/0x1020 net/ipv4/igmp.c:2033
> ip_mc_msfilter+0x5e5/0xcf0 net/ipv4/igmp.c:2403
> do_ip_setsockopt.isra.12+0x2d47/0x38c0 net/ipv4/ip_sockglue.c:959
> ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1256
> tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2740
> sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2844
> SYSC_setsockopt net/socket.c:1798 [inline]
> SyS_setsockopt+0x270/0x3a0 net/socket.c:1777
> entry_SYSCALL_64_fastpath+0x1f/0xbe
>
> Freed by task 30543:
> save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
> save_stack+0x43/0xd0 mm/kasan/kasan.c:513
> set_track mm/kasan/kasan.c:525 [inline]
> kasan_slab_free+0x72/0xc0 mm/kasan/kasan.c:590
> slab_free_hook mm/slub.c:1357 [inline]
> slab_free_freelist_hook mm/slub.c:1379 [inline]
> slab_free mm/slub.c:2961 [inline]
> kfree+0xe8/0x2b0 mm/slub.c:3882
> ip_mc_clear_src+0x69/0x1c0 net/ipv4/igmp.c:2078
> ip_mc_dec_group+0x19a/0x470 net/ipv4/igmp.c:1618
> ip_mc_drop_socket+0x145/0x230 net/ipv4/igmp.c:2609
> inet_release+0x4e/0x1c0 net/ipv4/af_inet.c:411
> sock_release+0x8d/0x1e0 net/socket.c:597
> sock_close+0x16/0x20 net/socket.c:1072
> __fput+0x332/0x7f0 fs/file_table.c:209
> ____fput+0x15/0x20 fs/file_table.c:245
> task_work_run+0x19b/0x270 kernel/task_work.c:116
> exit_task_work include/linux/task_work.h:21 [inline]
> do_exit+0x18a3/0x2820 kernel/exit.c:878
> do_group_exit+0x149/0x420 kernel/exit.c:982
> get_signal+0x76d/0x1790 kernel/signal.c:2318
> do_signal+0xd2/0x2130 arch/x86/kernel/signal.c:808
> exit_to_usermode_loop+0x17a/0x210 arch/x86/entry/common.c:157
> prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline]
> syscall_return_slowpath+0x3ba/0x410 arch/x86/entry/common.c:263
> entry_SYSCALL_64_fastpath+0xbc/0xbe
>
> The buggy address belongs to the object at ffff88003053c1a0
> which belongs to the cache kmalloc-64 of size 64
> The buggy address is located 0 bytes inside of
> 64-byte region [ffff88003053c1a0, ffff88003053c1e0)
> The buggy address belongs to the page:
> page:ffffea0000c14f00 count:1 mapcount:0 mapping: (null)
> index:0x0 compound_mapcount: 0
> flags: 0x100000000008100(slab|head)
> raw: 0100000000008100 0000000000000000 0000000000000000 0000000100140014
> raw: ffffea0000c2f520 ffffea0000e20aa0 ffff88003e80f740 0000000000000000
> page dumped because: kasan: bad access detected
>
> Memory state around the buggy address:
> ffff88003053c080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88003053c100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> >ffff88003053c180: fc fc fc fc fb fb fb fb fb fb fb fb fc fc fc fc
> ^
> ffff88003053c200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ffff88003053c280: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> ==================================================================

I have the feeling that ip_mc_clear_src() is called too soon.

We should call it once all users have released their reference.

I am not sure we have to call it after the RCU grace period,
more analysis of the code is needed.

diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 44fd86de2823dd17de16276a8ec01b190e69b8b4..f172d251c5f2cda8fc8bedd65fa16cdfe33a4d40 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -174,6 +174,7 @@ static int ip_mc_add_src(struct in_device *in_dev, __be32 *pmca, int sfmode,
static void ip_ma_put(struct ip_mc_list *im)
{
if (atomic_dec_and_test(&im->refcnt)) {
+ ip_mc_clear_src(im);
in_dev_put(im->interface);
kfree_rcu(im, rcu);
}
@@ -1615,7 +1616,6 @@ void ip_mc_dec_group(struct in_device *in_dev, __be32 addr)
*ip = i->next_rcu;
in_dev->mc_count--;
igmp_group_dropped(i);
- ip_mc_clear_src(i);

if (!in_dev->dead)
ip_rt_multicast_event(in_dev);

Next message: Tahsin Erdogan: "Re: [PATCH 09/28] ext4: extended attribute value size limit is enforced by vfs"
Previous message: Keith Busch: "Re: [PATCH V2 1/1] nvme: fix multiple ctrl removal scheduling"
In reply to: Andrey Konovalov: "net/ipv4: use-after-free in add_grec"
Next in thread: Cong Wang: "Re: net/ipv4: use-after-free in add_grec"
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