1. 15 Feb, 2023 1 commit
    • Munehisa Kamata's avatar
      sched/psi: Fix use-after-free in ep_remove_wait_queue() · c2dbe32d
      Munehisa Kamata authored
      If a non-root cgroup gets removed when there is a thread that registered
      trigger and is polling on a pressure file within the cgroup, the polling
      waitqueue gets freed in the following path:
      
       do_rmdir
         cgroup_rmdir
           kernfs_drain_open_files
             cgroup_file_release
               cgroup_pressure_release
                 psi_trigger_destroy
      
      However, the polling thread still has a reference to the pressure file and
      will access the freed waitqueue when the file is closed or upon exit:
      
       fput
         ep_eventpoll_release
           ep_free
             ep_remove_wait_queue
               remove_wait_queue
      
      This results in use-after-free as pasted below.
      
      The fundamental problem here is that cgroup_file_release() (and
      consequently waitqueue's lifetime) is not tied to the file's real lifetime.
      Using wake_up_pollfree() here might be less than ideal, but it is in line
      with the comment at commit 42288cb4 ("wait: add wake_up_pollfree()")
      since the waitqueue's lifetime is not tied to file's one and can be
      considered as another special case. While this would be fixable by somehow
      making cgroup_file_release() be tied to the fput(), it would require
      sizable refactoring at cgroups or higher layer which might be more
      justifiable if we identify more cases like this.
      
        BUG: KASAN: use-after-free in _raw_spin_lock_irqsave+0x60/0xc0
        Write of size 4 at addr ffff88810e625328 by task a.out/4404
      
      	CPU: 19 PID: 4404 Comm: a.out Not tainted 6.2.0-rc6 #38
      	Hardware name: Amazon EC2 c5a.8xlarge/, BIOS 1.0 10/16/2017
      	Call Trace:
      	<TASK>
      	dump_stack_lvl+0x73/0xa0
      	print_report+0x16c/0x4e0
      	kasan_report+0xc3/0xf0
      	kasan_check_range+0x2d2/0x310
      	_raw_spin_lock_irqsave+0x60/0xc0
      	remove_wait_queue+0x1a/0xa0
      	ep_free+0x12c/0x170
      	ep_eventpoll_release+0x26/0x30
      	__fput+0x202/0x400
      	task_work_run+0x11d/0x170
      	do_exit+0x495/0x1130
      	do_group_exit+0x100/0x100
      	get_signal+0xd67/0xde0
      	arch_do_signal_or_restart+0x2a/0x2b0
      	exit_to_user_mode_prepare+0x94/0x100
      	syscall_exit_to_user_mode+0x20/0x40
      	do_syscall_64+0x52/0x90
      	entry_SYSCALL_64_after_hwframe+0x63/0xcd
      	</TASK>
      
       Allocated by task 4404:
      
      	kasan_set_track+0x3d/0x60
      	__kasan_kmalloc+0x85/0x90
      	psi_trigger_create+0x113/0x3e0
      	pressure_write+0x146/0x2e0
      	cgroup_file_write+0x11c/0x250
      	kernfs_fop_write_iter+0x186/0x220
      	vfs_write+0x3d8/0x5c0
      	ksys_write+0x90/0x110
      	do_syscall_64+0x43/0x90
      	entry_SYSCALL_64_after_hwframe+0x63/0xcd
      
       Freed by task 4407:
      
      	kasan_set_track+0x3d/0x60
      	kasan_save_free_info+0x27/0x40
      	____kasan_slab_free+0x11d/0x170
      	slab_free_freelist_hook+0x87/0x150
      	__kmem_cache_free+0xcb/0x180
      	psi_trigger_destroy+0x2e8/0x310
      	cgroup_file_release+0x4f/0xb0
      	kernfs_drain_open_files+0x165/0x1f0
      	kernfs_drain+0x162/0x1a0
      	__kernfs_remove+0x1fb/0x310
      	kernfs_remove_by_name_ns+0x95/0xe0
      	cgroup_addrm_files+0x67f/0x700
      	cgroup_destroy_locked+0x283/0x3c0
      	cgroup_rmdir+0x29/0x100
      	kernfs_iop_rmdir+0xd1/0x140
      	vfs_rmdir+0xfe/0x240
      	do_rmdir+0x13d/0x280
      	__x64_sys_rmdir+0x2c/0x30
      	do_syscall_64+0x43/0x90
      	entry_SYSCALL_64_after_hwframe+0x63/0xcd
      
      Fixes: 0e94682b ("psi: introduce psi monitor")
      Signed-off-by: default avatarMunehisa Kamata <kamatam@amazon.com>
      Signed-off-by: default avatarMengchi Cheng <mengcc@amazon.com>
      Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
      Acked-by: default avatarSuren Baghdasaryan <surenb@google.com>
      Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
      Cc: stable@vger.kernel.org
      Link: https://lore.kernel.org/lkml/20230106224859.4123476-1-kamatam@amazon.com/
      Link: https://lore.kernel.org/r/20230214212705.4058045-1-kamatam@amazon.com
      c2dbe32d
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