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SubjectRe: net/ppp: use-after-free in ppp_unregister_channel
On Wed, Mar 16, 2016 at 11:14:42PM +0800, Baozeng Ding wrote:
> Dear all,
> I've got the following use-after-free report while running syzkaller
> fuzzer. Unfortunately no reproducer. It was found in the Linux kernel
> version(4.4, on commit 9638685e32af961943b679fcb72d4ddd458eb18f).
>
> ==================================================================
> BUG: KASAN: use-after-free in ppp_unregister_channel+0x372/0x3a0 at
> addr ffff880064e217e0
> Read of size 8 by task syz-executor/11581
> =============================================================================
> BUG net_namespace (Not tainted): kasan: bad access detected
> -----------------------------------------------------------------------------
>
> Disabling lock debugging due to kernel taint
> INFO: Allocated in copy_net_ns+0x6b/0x1a0 age=92569 cpu=3 pid=6906
> [< none >] ___slab_alloc+0x4c7/0x500 kernel/mm/slub.c:2440
> [< none >] __slab_alloc+0x4c/0x90 kernel/mm/slub.c:2469
> [< inline >] slab_alloc_node kernel/mm/slub.c:2532
> [< inline >] slab_alloc kernel/mm/slub.c:2574
> [< none >] kmem_cache_alloc+0x23a/0x2b0 kernel/mm/slub.c:2579
> [< inline >] kmem_cache_zalloc kernel/include/linux/slab.h:597
> [< inline >] net_alloc kernel/net/core/net_namespace.c:325
> [< none >] copy_net_ns+0x6b/0x1a0 kernel/net/core/net_namespace.c:360
> [< none >] create_new_namespaces+0x2f6/0x610 kernel/kernel/nsproxy.c:95
> [< none >] copy_namespaces+0x297/0x320 kernel/kernel/nsproxy.c:150
> [< none >] copy_process.part.35+0x1bf4/0x5760 kernel/kernel/fork.c:1451
> [< inline >] copy_process kernel/kernel/fork.c:1274
> [< none >] _do_fork+0x1bc/0xcb0 kernel/kernel/fork.c:1723
> [< inline >] SYSC_clone kernel/kernel/fork.c:1832
> [< none >] SyS_clone+0x37/0x50 kernel/kernel/fork.c:1826
> [< none >] entry_SYSCALL_64_fastpath+0x16/0x7a kernel/arch/x86/entry/entry_64.S:185
>
> INFO: Freed in net_drop_ns+0x67/0x80 age=575 cpu=2 pid=2631
> [< none >] __slab_free+0x1fc/0x320 kernel/mm/slub.c:2650
> [< inline >] slab_free kernel/mm/slub.c:2805
> [< none >] kmem_cache_free+0x2a0/0x330 kernel/mm/slub.c:2814
> [< inline >] net_free kernel/net/core/net_namespace.c:341
> [< none >] net_drop_ns+0x67/0x80 kernel/net/core/net_namespace.c:348
> [< none >] cleanup_net+0x4e5/0x600 kernel/net/core/net_namespace.c:448
> [< none >] process_one_work+0x794/0x1440 kernel/kernel/workqueue.c:2036
> [< none >] worker_thread+0xdb/0xfc0 kernel/kernel/workqueue.c:2170
> [< none >] kthread+0x23f/0x2d0 kernel/drivers/block/aoe/aoecmd.c:1303
> [< none >] ret_from_fork+0x3f/0x70 kernel/arch/x86/entry/entry_64.S:468
> INFO: Slab 0xffffea0001938800 objects=3 used=0 fp=0xffff880064e20000
> flags=0x5fffc0000004080
> INFO: Object 0xffff880064e20000 @offset=0 fp=0xffff880064e24200
>
> CPU: 1 PID: 11581 Comm: syz-executor Tainted: G B 4.4.0+
> #5
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.8.2-0-g33fbe13 by qemu-project.org 04/01/2014
> 00000000ffffffff ffff8800662c7790 ffffffff8292049d ffff88003e36a300
> ffff880064e20000 ffff880064e20000 ffff8800662c77c0 ffffffff816f2054
> ffff88003e36a300 ffffea0001938800 ffff880064e20000 0000000000000000
> Call Trace:
> [< inline >] __dump_stack kernel/lib/dump_stack.c:15
> [<ffffffff8292049d>] dump_stack+0x6f/0xa2 kernel/lib/dump_stack.c:50
> [<ffffffff816f2054>] print_trailer+0xf4/0x150 kernel/mm/slub.c:654
> [<ffffffff816f875f>] object_err+0x2f/0x40 kernel/mm/slub.c:661
> [< inline >] print_address_description kernel/mm/kasan/report.c:138
> [<ffffffff816fb0c5>] kasan_report_error+0x215/0x530 kernel/mm/kasan/report.c:236
> [< inline >] kasan_report kernel/mm/kasan/report.c:259
> [<ffffffff816fb4de>] __asan_report_load8_noabort+0x3e/0x40 kernel/mm/kasan/report.c:280
> [< inline >] ? ppp_pernet kernel/include/linux/compiler.h:218
> [<ffffffff83ad71b2>] ? ppp_unregister_channel+0x372/0x3a0 kernel/drivers/net/ppp/ppp_generic.c:2392
> [< inline >] ppp_pernet kernel/include/linux/compiler.h:218
> [<ffffffff83ad71b2>] ppp_unregister_channel+0x372/0x3a0 kernel/drivers/net/ppp/ppp_generic.c:2392
> [< inline >] ? ppp_pernet kernel/drivers/net/ppp/ppp_generic.c:293
> [<ffffffff83ad6f26>] ? ppp_unregister_channel+0xe6/0x3a0 kernel/drivers/net/ppp/ppp_generic.c:2392
> [<ffffffff83ae18f3>] ppp_asynctty_close+0xa3/0x130 kernel/drivers/net/ppp/ppp_async.c:241
> [<ffffffff83ae1850>] ? async_lcp_peek+0x5b0/0x5b0 kernel/drivers/net/ppp/ppp_async.c:1000
> [<ffffffff82c33239>] tty_ldisc_close.isra.1+0x99/0xe0 kernel/drivers/tty/tty_ldisc.c:478
> [<ffffffff82c332c0>] tty_ldisc_kill+0x40/0x170 kernel/drivers/tty/tty_ldisc.c:744
> [<ffffffff82c34943>] tty_ldisc_release+0x1b3/0x260 kernel/drivers/tty/tty_ldisc.c:772
> [<ffffffff82c1ef21>] tty_release+0xac1/0x13e0 kernel/drivers/tty/tty_io.c:1901
> [<ffffffff82c1e460>] ? release_tty+0x320/0x320 kernel/drivers/tty/tty_io.c:1688
> [<ffffffff8174de36>] __fput+0x236/0x780 kernel/fs/file_table.c:208
> [<ffffffff8174e405>] ____fput+0x15/0x20 kernel/fs/file_table.c:244
> [<ffffffff813595ab>] task_work_run+0x16b/0x200 kernel/kernel/task_work.c:115
> [< inline >] exit_task_work kernel/include/linux/task_work.h:21
> [<ffffffff81307105>] do_exit+0x8b5/0x2c60 kernel/kernel/exit.c:750
> [<ffffffff813fdd20>] ? debug_check_no_locks_freed+0x290/0x290 kernel/kernel/locking/lockdep.c:4123
> [<ffffffff81306850>] ? mm_update_next_owner+0x6f0/0x6f0 kernel/kernel/exit.c:357
> [<ffffffff813215e6>] ? __dequeue_signal+0x136/0x470 kernel/kernel/signal.c:550
> [<ffffffff8132067b>] ? recalc_sigpending_tsk+0x13b/0x180 kernel/kernel/signal.c:145
> [<ffffffff81309628>] do_group_exit+0x108/0x330 kernel/kernel/exit.c:880
> [<ffffffff8132b9d4>] get_signal+0x5e4/0x14f0 kernel/kernel/signal.c:2307
> [< inline >] ? kretprobe_table_lock kernel/kernel/kprobes.c:1113
> [<ffffffff8151d355>] ? kprobe_flush_task+0xb5/0x450 kernel/kernel/kprobes.c:1158
> [<ffffffff8115f7d3>] do_signal+0x83/0x1c90 kernel/arch/x86/kernel/signal.c:712
> [<ffffffff8151d2a0>] ? recycle_rp_inst+0x310/0x310 kernel/include/linux/list.h:655
> [<ffffffff8115f750>] ? setup_sigcontext+0x780/0x780 kernel/arch/x86/kernel/signal.c:165
> [<ffffffff81380864>] ? finish_task_switch+0x424/0x5f0 kernel/kernel/sched/core.c:2692
> [< inline >] ? finish_lock_switch kernel/kernel/sched/sched.h:1099
> [<ffffffff81380560>] ? finish_task_switch+0x120/0x5f0 kernel/kernel/sched/core.c:2678
> [< inline >] ? context_switch kernel/kernel/sched/core.c:2807
> [<ffffffff85d794e9>] ? __schedule+0x919/0x1bd0 kernel/kernel/sched/core.c:3283
> [<ffffffff81003901>] exit_to_usermode_loop+0xf1/0x1a0 kernel/arch/x86/entry/common.c:247
> [< inline >] prepare_exit_to_usermode kernel/arch/x86/entry/common.c:282
> [<ffffffff810062ef>] syscall_return_slowpath+0x19f/0x210 kernel/arch/x86/entry/common.c:344
> [<ffffffff85d88022>] int_ret_from_sys_call+0x25/0x9f kernel/arch/x86/entry/entry_64.S:281

A network namespace has been removed while a ppp_async channel was
still registered in it. Then, unregistering this channel triggered the
bug because ppp_unregister_channel() tried to access its per-netns data
in the defunct namespace.

This scenario can happen at least with ppp_async and ppp_synctty, where
the userspace program and the PPP channel it handles can leave in
separate namespaces.

Thanks for the report, I can reproduce the bug and will work on a fix.

Guillaume

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