Messages in this thread | | | Date | Sun, 29 Oct 2017 13:45:09 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: KASAN: use-after-free Write in detach_if_pending |
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On Fri, 27 Oct 2017, syzbot wrote:
Cc'ed network folks.
> syzkaller hit the following crash on e7989f973ae1b90ec7c0b671c81f7f553affccbe > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master > compiler: gcc (GCC) 7.1.1 20170620 > .config is attached > Raw console output is attached. > C reproducer is attached > syzkaller reproducer is attached. See https://goo.gl/kgGztJ > for information about syzkaller reproducers > > > BUG: KASAN: use-after-free in __write_once_size include/linux/compiler.h:305 > [inline] > BUG: KASAN: use-after-free in __hlist_del include/linux/list.h:648 [inline] > BUG: KASAN: use-after-free in detach_timer kernel/time/timer.c:791 [inline] > BUG: KASAN: use-after-free in detach_if_pending+0x557/0x610 > kernel/time/timer.c:808 > Write of size 8 at addr ffff8801d3bab780 by task syzkaller900516/2986
That's just the point where this gets detected.
> CPU: 1 PID: 2986 Comm: syzkaller900516 Not tainted 4.13.0+ #82
> __hlist_del include/linux/list.h:648 [inline] > detach_timer kernel/time/timer.c:791 [inline] > detach_if_pending+0x557/0x610 kernel/time/timer.c:808 > try_to_del_timer_sync+0xa2/0x120 kernel/time/timer.c:1182 > del_timer_sync+0x18a/0x240 kernel/time/timer.c:1247 > tun_flow_uninit drivers/net/tun.c:1104 [inline] > tun_free_netdev+0x105/0x1b0 drivers/net/tun.c:1776
^^^^^^^^^^^^ This shouldn't be called I think
> netdev_run_todo+0x870/0xca0 net/core/dev.c:7864 > rtnl_unlock+0xe/0x10 net/core/rtnetlink.c:106 > tun_detach drivers/net/tun.c:588 [inline] > tun_chr_close+0x49/0x60 drivers/net/tun.c:2609 > __fput+0x333/0x7f0 fs/file_table.c:210 > ____fput+0x15/0x20 fs/file_table.c:246 > task_work_run+0x199/0x270 kernel/task_work.c:112 > exit_task_work include/linux/task_work.h:21 [inline] > do_exit+0xa52/0x1b40 kernel/exit.c:865
Here is the allocation path
> alloc_netdev_mqs+0x16e/0xed0 net/core/dev.c:8018 > tun_set_iff drivers/net/tun.c:2022 [inline] > __tun_chr_ioctl+0x12be/0x3d20 drivers/net/tun.c:2276 > tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2521 > vfs_ioctl fs/ioctl.c:45 [inline] > do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685 > SYSC_ioctl fs/ioctl.c:700 [inline] > SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 > entry_SYSCALL_64_fastpath+0x1f/0xbe
And this is free.
> netdev_freemem net/core/dev.c:7970 [inline] > free_netdev+0x2cf/0x360 net/core/dev.c:8132 > tun_set_iff drivers/net/tun.c:2105 [inline]
err_free_flow: tun_flow_uninit(tun); <--------
> __tun_chr_ioctl+0x2cf6/0x3d20 drivers/net/tun.c:2276 > tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2521 > vfs_ioctl fs/ioctl.c:45 [inline] > do_vfs_ioctl+0x1b1/0x1530 fs/ioctl.c:685 > SYSC_ioctl fs/ioctl.c:700 [inline] > SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691 > entry_SYSCALL_64_fastpath+0x1f/0xbe
So it's the TUNSETIFF ioctl which first allocates and then frees in the errorpath of tun_set_iff.
But for some reason this sticks and the exit of that task does it again, which triggers KASAN in the innocent timer code.
Thanks,
tglx
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