1. 22 Jan, 2019 2 commits
    • Dmitry Safonov's avatar
      tty: Hold tty_ldisc_lock() during tty_reopen() · e6a4caa0
      Dmitry Safonov authored
      commit 83d817f4 upstream.
      
      tty_ldisc_reinit() doesn't race with neither tty_ldisc_hangup()
      nor set_ldisc() nor tty_ldisc_release() as they use tty lock.
      But it races with anyone who expects line discipline to be the same
      after hoding read semaphore in tty_ldisc_ref().
      
      We've seen the following crash on v4.9.108 stable:
      
      BUG: unable to handle kernel paging request at 0000000000002260
      IP: [..] n_tty_receive_buf_common+0x5f/0x86d
      Workqueue: events_unbound flush_to_ldisc
      Call Trace:
       [..] n_tty_receive_buf2
       [..] tty_ldisc_receive_buf
       [..] flush_to_ldisc
       [..] process_one_work
       [..] worker_thread
       [..] kthread
       [..] ret_from_fork
      
      tty_ldisc_reinit() should be called with ldisc_sem hold for writing,
      which will protect any reader against line discipline changes.
      
      Cc: Jiri Slaby <jslaby@suse.com>
      Cc: stable@vger.kernel.org # b027e229 ("tty: fix data race between tty_init_dev and flush of buf")
      Reviewed-by: default avatarJiri Slaby <jslaby@suse.cz>
      Reported-by: syzbot+3aa9784721dfb90e984d@syzkaller.appspotmail.com
      Tested-by: default avatarMark Rutland <mark.rutland@arm.com>
      Tested-by: default avatarTetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
      Signed-off-by: default avatarDmitry Safonov <dima@arista.com>
      Tested-by: default avatarTycho Andersen <tycho@tycho.ws>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      e6a4caa0
    • Dmitry Safonov's avatar
      tty/ldsem: Wake up readers after timed out down_write() · 028c13f7
      Dmitry Safonov authored
      commit 231f8fd0 upstream.
      
      ldsem_down_read() will sleep if there is pending writer in the queue.
      If the writer times out, readers in the queue should be woken up,
      otherwise they may miss a chance to acquire the semaphore until the last
      active reader will do ldsem_up_read().
      
      There was a couple of reports where there was one active reader and
      other readers soft locked up:
        Showing all locks held in the system:
        2 locks held by khungtaskd/17:
         #0:  (rcu_read_lock){......}, at: watchdog+0x124/0x6d1
         #1:  (tasklist_lock){.+.+..}, at: debug_show_all_locks+0x72/0x2d3
        2 locks held by askfirst/123:
         #0:  (&tty->ldisc_sem){.+.+.+}, at: ldsem_down_read+0x46/0x58
         #1:  (&ldata->atomic_read_lock){+.+...}, at: n_tty_read+0x115/0xbe4
      
      Prevent readers wait for active readers to release ldisc semaphore.
      
      Link: lkml.kernel.org/r/20171121132855.ajdv4k6swzhvktl6@wfg-t540p.sh.intel.com
      Link: lkml.kernel.org/r/20180907045041.GF1110@shao2-debian
      Cc: Jiri Slaby <jslaby@suse.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: stable@vger.kernel.org
      Reported-by: default avatarkernel test robot <rong.a.chen@intel.com>
      Signed-off-by: default avatarDmitry Safonov <dima@arista.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      028c13f7
  2. 16 Jan, 2019 38 commits