• Daniel Borkmann's avatar
    tun, bpf: fix suspicious RCU usage in tun_{attach, detach}_filter · 5a5abb1f
    Daniel Borkmann authored
    Sasha Levin reported a suspicious rcu_dereference_protected() warning
    found while fuzzing with trinity that is similar to this one:
    
      [   52.765684] net/core/filter.c:2262 suspicious rcu_dereference_protected() usage!
      [   52.765688] other info that might help us debug this:
      [   52.765695] rcu_scheduler_active = 1, debug_locks = 1
      [   52.765701] 1 lock held by a.out/1525:
      [   52.765704]  #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff816a64b7>] rtnl_lock+0x17/0x20
      [   52.765721] stack backtrace:
      [   52.765728] CPU: 1 PID: 1525 Comm: a.out Not tainted 4.5.0+ #264
      [...]
      [   52.765768] Call Trace:
      [   52.765775]  [<ffffffff813e488d>] dump_stack+0x85/0xc8
      [   52.765784]  [<ffffffff810f2fa5>] lockdep_rcu_suspicious+0xd5/0x110
      [   52.765792]  [<ffffffff816afdc2>] sk_detach_filter+0x82/0x90
      [   52.765801]  [<ffffffffa0883425>] tun_detach_filter+0x35/0x90 [tun]
      [   52.765810]  [<ffffffffa0884ed4>] __tun_chr_ioctl+0x354/0x1130 [tun]
      [   52.765818]  [<ffffffff8136fed0>] ? selinux_file_ioctl+0x130/0x210
      [   52.765827]  [<ffffffffa0885ce3>] tun_chr_ioctl+0x13/0x20 [tun]
      [   52.765834]  [<ffffffff81260ea6>] do_vfs_ioctl+0x96/0x690
      [   52.765843]  [<ffffffff81364af3>] ? security_file_ioctl+0x43/0x60
      [   52.765850]  [<ffffffff81261519>] SyS_ioctl+0x79/0x90
      [   52.765858]  [<ffffffff81003ba2>] do_syscall_64+0x62/0x140
      [   52.765866]  [<ffffffff817d563f>] entry_SYSCALL64_slow_path+0x25/0x25
    
    Same can be triggered with PROVE_RCU (+ PROVE_RCU_REPEATEDLY) enabled
    from tun_attach_filter() when user space calls ioctl(tun_fd, TUN{ATTACH,
    DETACH}FILTER, ...) for adding/removing a BPF filter on tap devices.
    
    Since the fix in f91ff5b9 ("net: sk_{detach|attach}_filter() rcu
    fixes") sk_attach_filter()/sk_detach_filter() now dereferences the
    filter with rcu_dereference_protected(), checking whether socket lock
    is held in control path.
    
    Since its introduction in 99405162 ("tun: socket filter support"),
    tap filters are managed under RTNL lock from __tun_chr_ioctl(). Thus the
    sock_owned_by_user(sk) doesn't apply in this specific case and therefore
    triggers the false positive.
    
    Extend the BPF API with __sk_attach_filter()/__sk_detach_filter() pair
    that is used by tap filters and pass in lockdep_rtnl_is_held() for the
    rcu_dereference_protected() checks instead.
    Reported-by: default avatarSasha Levin <sasha.levin@oracle.com>
    Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    5a5abb1f
filter.h 15.4 KB