• Jiri Slaby's avatar
    TTY: serial_core, add ->install · b6dc42e5
    Jiri Slaby authored
    commit 4cdd17ba upstream.
    
    We need to compute the uart state only on the first open. This is
    usually what is done in the ->install hook. serial_core used to do this
    in ->open on every open. So move it to ->install.
    
    As a side effect, it ensures the state is set properly in the window
    after tty_init_dev is called, but before uart_open. This fixes a bunch
    of races between tty_open and flush_to_ldisc we were dealing with
    recently.
    
    One of such bugs was attempted to fix in commit fedb5760 (serial:
    fix race between flush_to_ldisc and tty_open), but it only took care of
    a couple of functions (uart_start and uart_unthrottle).  I was able to
    reproduce the crash on a SLE system, but in uart_write_room which is
    also called from flush_to_ldisc via process_echoes. I was *unable* to
    reproduce the bug locally. It is due to having this patch in my queue
    since 2012!
    
     general protection fault: 0000 [#1] SMP KASAN PTI
     CPU: 1 PID: 5 Comm: kworker/u4:0 Tainted: G             L 4.12.14-396-default #1 SLE15-SP1 (unreleased)
     Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-0-ga698c89-prebuilt.qemu.org 04/01/2014
     Workqueue: events_unbound flush_to_ldisc
     task: ffff8800427d8040 task.stack: ffff8800427f0000
     RIP: 0010:uart_write_room+0xc4/0x590
     RSP: 0018:ffff8800427f7088 EFLAGS: 00010202
     RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
     RDX: 000000000000002f RSI: 00000000000000ee RDI: ffff88003888bd90
     RBP: ffffffffb9545850 R08: 0000000000000001 R09: 0000000000000400
     R10: ffff8800427d825c R11: 000000000000006e R12: 1ffff100084fee12
     R13: ffffc900004c5000 R14: ffff88003888bb28 R15: 0000000000000178
     FS:  0000000000000000(0000) GS:ffff880043300000(0000) knlGS:0000000000000000
     CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
     CR2: 0000561da0794148 CR3: 000000000ebf4000 CR4: 00000000000006e0
     Call Trace:
      tty_write_room+0x6d/0xc0
      __process_echoes+0x55/0x870
      n_tty_receive_buf_common+0x105e/0x26d0
      tty_ldisc_receive_buf+0xb7/0x1c0
      tty_port_default_receive_buf+0x107/0x180
      flush_to_ldisc+0x35d/0x5c0
    ...
    
    0 in rbx means tty->driver_data is NULL in uart_write_room. 0x178 is
    tried to be dereferenced (0x178 >> 3 is 0x2f in rdx) at
    uart_write_room+0xc4. 0x178 is exactly (struct uart_state *)NULL->refcount
    used in uart_port_lock from uart_write_room.
    
    So revert the upstream commit here as my local patch should fix the
    whole family.
    Signed-off-by: default avatarJiri Slaby <jslaby@suse.cz>
    Cc: Li RongQing <lirongqing@baidu.com>
    Cc: Wang Li <wangli39@baidu.com>
    Cc: Zhang Yu <zhangyu31@baidu.com>
    Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    Cc: stable <stable@vger.kernel.org>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    b6dc42e5
serial_core.c 76.6 KB