• Yonghong Song's avatar
    bpf/tracing: fix a deadlock in perf_event_detach_bpf_prog · 3a38bb98
    Yonghong Song authored
    syzbot reported a possible deadlock in perf_event_detach_bpf_prog.
    The error details:
      ======================================================
      WARNING: possible circular locking dependency detected
      4.16.0-rc7+ #3 Not tainted
      ------------------------------------------------------
      syz-executor7/24531 is trying to acquire lock:
       (bpf_event_mutex){+.+.}, at: [<000000008a849b07>] perf_event_detach_bpf_prog+0x92/0x3d0 kernel/trace/bpf_trace.c:854
    
      but task is already holding lock:
       (&mm->mmap_sem){++++}, at: [<0000000038768f87>] vm_mmap_pgoff+0x198/0x280 mm/util.c:353
    
      which lock already depends on the new lock.
    
      the existing dependency chain (in reverse order) is:
    
      -> #1 (&mm->mmap_sem){++++}:
           __might_fault+0x13a/0x1d0 mm/memory.c:4571
           _copy_to_user+0x2c/0xc0 lib/usercopy.c:25
           copy_to_user include/linux/uaccess.h:155 [inline]
           bpf_prog_array_copy_info+0xf2/0x1c0 kernel/bpf/core.c:1694
           perf_event_query_prog_array+0x1c7/0x2c0 kernel/trace/bpf_trace.c:891
           _perf_ioctl kernel/events/core.c:4750 [inline]
           perf_ioctl+0x3e1/0x1480 kernel/events/core.c:4770
           vfs_ioctl fs/ioctl.c:46 [inline]
           do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
           SYSC_ioctl fs/ioctl.c:701 [inline]
           SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
           do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
           entry_SYSCALL_64_after_hwframe+0x42/0xb7
    
      -> #0 (bpf_event_mutex){+.+.}:
           lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
           __mutex_lock_common kernel/locking/mutex.c:756 [inline]
           __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
           mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
           perf_event_detach_bpf_prog+0x92/0x3d0 kernel/trace/bpf_trace.c:854
           perf_event_free_bpf_prog kernel/events/core.c:8147 [inline]
           _free_event+0xbdb/0x10f0 kernel/events/core.c:4116
           put_event+0x24/0x30 kernel/events/core.c:4204
           perf_mmap_close+0x60d/0x1010 kernel/events/core.c:5172
           remove_vma+0xb4/0x1b0 mm/mmap.c:172
           remove_vma_list mm/mmap.c:2490 [inline]
           do_munmap+0x82a/0xdf0 mm/mmap.c:2731
           mmap_region+0x59e/0x15a0 mm/mmap.c:1646
           do_mmap+0x6c0/0xe00 mm/mmap.c:1483
           do_mmap_pgoff include/linux/mm.h:2223 [inline]
           vm_mmap_pgoff+0x1de/0x280 mm/util.c:355
           SYSC_mmap_pgoff mm/mmap.c:1533 [inline]
           SyS_mmap_pgoff+0x462/0x5f0 mm/mmap.c:1491
           SYSC_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
           SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:91
           do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
           entry_SYSCALL_64_after_hwframe+0x42/0xb7
    
      other info that might help us debug this:
    
       Possible unsafe locking scenario:
    
             CPU0                    CPU1
             ----                    ----
        lock(&mm->mmap_sem);
                                     lock(bpf_event_mutex);
                                     lock(&mm->mmap_sem);
        lock(bpf_event_mutex);
    
       *** DEADLOCK ***
      ======================================================
    
    The bug is introduced by Commit f371b304 ("bpf/tracing: allow
    user space to query prog array on the same tp") where copy_to_user,
    which requires mm->mmap_sem, is called inside bpf_event_mutex lock.
    At the same time, during perf_event file descriptor close,
    mm->mmap_sem is held first and then subsequent
    perf_event_detach_bpf_prog needs bpf_event_mutex lock.
    Such a senario caused a deadlock.
    
    As suggested by Daniel, moving copy_to_user out of the
    bpf_event_mutex lock should fix the problem.
    
    Fixes: f371b304 ("bpf/tracing: allow user space to query prog array on the same tp")
    Reported-by: syzbot+dc5ca0e4c9bfafaf2bae@syzkaller.appspotmail.com
    Signed-off-by: default avatarYonghong Song <yhs@fb.com>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    3a38bb98
core.c 45.7 KB