xserver: Branch 'server-21.1-branch'

[GitLab Mirror]

 dix/devices.c |    3 +++
 1 file changed, 3 insertions(+)

New commits:
commit ba830583e6a8e9a78f09e2d723813c03142b11f6
Author: tholin <thomas.lindroth at gmail.com>
Date:   Tue Jan 4 12:08:11 2022 +0000

    dix: Hold input lock for AttachDevice()
    
    Fix the following race:
    
    Possible data race during read of size 8 at 0xA112510 by thread #6
    Locks held: 1, at address 0x366B40
       at 0x14C8B9: GetMaster (devices.c:2691)
       by 0x15CFC5: IsFloating (events.c:346)
       by 0x2B9554: miPointerGetScreen (mipointer.c:527)
       by 0x1A5136: xf86PostButtonEventM (xf86Xinput.c:1379)
       by 0x1A52BD: xf86PostButtonEvent (xf86Xinput.c:1345)
       by 0x485F45B: EvdevProcessEvent (in /usr/lib64/xorg/modules/input/evdev_drv.so)
       by 0x485FDAC: EvdevReadInput (in /usr/lib64/xorg/modules/input/evdev_drv.so)
       by 0x195427: xf86ReadInput (xf86Events.c:247)
       by 0x2CC113: InputReady (inputthread.c:180)
       by 0x2CE4EA: ospoll_wait (ospoll.c:657)
       by 0x2CC077: InputThreadDoWork (inputthread.c:369)
       by 0x484A336: mythread_wrapper (hg_intercepts.c:406)
    
    This conflicts with a previous write of size 8 by thread #1
    Locks held: none
       at 0x14D2C6: AttachDevice (devices.c:2609)
       by 0x15CF85: ReattachToOldMaster (events.c:1457)
       by 0x1647DD: DeactivateKeyboardGrab (events.c:1700)
       by 0x25D7F1: ProcXIUngrabDevice (xigrabdev.c:169)
       by 0x2552AD: ProcIDispatch (extinit.c:398)
       by 0x155291: Dispatch (dispatch.c:479)
       by 0x158CBA: dix_main (main.c:276)
       by 0x143A3D: main (stubmain.c:34)
     Address 0xa112510 is 336 bytes inside a block of size 904 alloc'd
       at 0x4846571: calloc (vg_replace_malloc.c:1328)
       by 0x14A0B3: AddInputDevice (devices.c:260)
       by 0x1A31A0: xf86ActivateDevice (xf86Xinput.c:365)
       by 0x1A4549: xf86NewInputDevice (xf86Xinput.c:948)
       by 0x1A4B44: NewInputDeviceRequest (xf86Xinput.c:1090)
       by 0x1B81FE: device_added (udev.c:282)
       by 0x1B8516: config_udev_init (udev.c:439)
       by 0x1B7091: config_init (config.c:50)
       by 0x197970: InitInput (xf86Init.c:814)
       by 0x158C6B: dix_main (main.c:250)
       by 0x143A3D: main (stubmain.c:34)
     Block was alloc'd by thread #1
    
    The steps to trigger the race are:
    1. Main thread does cleanup at mipointer.c:360 setting the slave device's
       miPointerPtr to null.
    2. Input thread use MIPOINTER in mipointer.c and get the slave's
       miPointerPtr = null.
    3. Main thread updates dev->master at devices.c:2609.
    4. MIPOINTER would now return the master's miPointerPtr but the input
       thread already got the slave's miPointerPtr in step 2 and segfaults by
       null ptr deref.
    
    Closes: https://gitlab.freedesktop.org/xorg/xserver/-/issues/1260
    Signed-off-by: Thomas Lindroth <thomas.lindroth at gmail.com>
    (cherry picked from commit dc7cb45482cea6ccec22d117ca0b489500b4d0a0)
    
    Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1874>

diff --git a/dix/devices.c b/dix/devices.c
index 77bac4924..5f6d32e53 100644
--- a/dix/devices.c
+++ b/dix/devices.c
@@ -2672,6 +2672,8 @@ AttachDevice(ClientPtr client, DeviceIntPtr dev, DeviceIntPtr master)
     if (IsFloating(dev) && !master && dev->enabled)
         return Success;
 
+    input_lock();
+
     /* free the existing sprite. */
     if (IsFloating(dev) && dev->spriteInfo->paired == dev) {
         screen = miPointerGetScreen(dev);
@@ -2715,6 +2717,7 @@ AttachDevice(ClientPtr client, DeviceIntPtr dev, DeviceIntPtr master)
         RecalculateMasterButtons(master);
     }
 
+    input_unlock();
     /* XXX: in theory, the MD should change back to its old, original
      * classes when the last SD is detached. Thanks to the XTEST devices,
      * we'll always have an SD attached until the MD is removed.