kernel/linux.git/drivers/gpu/drm/drm_auth.c, branch v5.10.92

drm: protect drm_master pointers in drm_lease.c

2021-09-18T11:40:19+00:00

[ Upstream commit 56f0729a510f92151682ff6c89f69724d5595d6e ] drm_file->master pointers should be protected by drm_device.master_mutex or drm_file.master_lookup_lock when being dereferenced. However, in drm_lease.c, there are multiple instances where drm_file->master is accessed and dereferenced while neither lock is held. This makes drm_lease.c vulnerable to use-after-free bugs. We address this issue in 2 ways: 1. Add a new drm_file_get_master() function that calls drm_master_get on drm_file->master while holding on to drm_file.master_lookup_lock. Since drm_master_get increments the reference count of master, this prevents master from being freed until we unreference it with drm_master_put. 2. In each case where drm_file->master is directly accessed and eventually dereferenced in drm_lease.c, we wrap the access in a call to the new drm_file_get_master function, then unreference the master pointer once we are done using it. Reported-by: Daniel Vetter Signed-off-by: Desmond Cheong Zhi Xi Reviewed-by: Emil Velikov Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-6-desmondcheongzx@gmail.com Signed-off-by: Sasha Levin

drm: serialize drm_file.master with a new spinlock

2021-09-18T11:40:19+00:00

[ Upstream commit 0b0860a3cf5eccf183760b1177a1dcdb821b0b66 ] Currently, drm_file.master pointers should be protected by drm_device.master_mutex when being dereferenced. This is because drm_file.master is not invariant for the lifetime of drm_file. If drm_file is not the creator of master, then drm_file.is_master is false, and a call to drm_setmaster_ioctl will invoke drm_new_set_master, which then allocates a new master for drm_file and puts the old master. Thus, without holding drm_device.master_mutex, the old value of drm_file.master could be freed while it is being used by another concurrent process. However, it is not always possible to lock drm_device.master_mutex to dereference drm_file.master. Through the fbdev emulation code, this might occur in a deep nest of other locks. But drm_device.master_mutex is also the outermost lock in the nesting hierarchy, so this leads to potential deadlocks. To address this, we introduce a new spin lock at the bottom of the lock hierarchy that only serializes drm_file.master. With this change, the value of drm_file.master changes only when both drm_device.master_mutex and drm_file.master_lookup_lock are held. Hence, any process holding either of those locks can ensure that the value of drm_file.master will not change concurrently. Since no lock depends on the new drm_file.master_lookup_lock, when drm_file.master is dereferenced, but drm_device.master_mutex cannot be held, we can safely protect the master pointer with drm_file.master_lookup_lock. Reported-by: Daniel Vetter Signed-off-by: Desmond Cheong Zhi Xi Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-5-desmondcheongzx@gmail.com Signed-off-by: Sasha Levin

Revert "drm: add a locked version of drm_is_current_master"

2021-06-30T12:47:30+00:00

commit f54b3ca7ea1e5e02f481cf4ca54568e57bd66086 upstream. This reverts commit 1815d9c86e3090477fbde066ff314a7e9721ee0f. Unfortunately this inverts the locking hierarchy, so back to the drawing board. Full lockdep splat below: ====================================================== WARNING: possible circular locking dependency detected 5.13.0-rc7-CI-CI_DRM_10254+ #1 Not tainted ------------------------------------------------------ kms_frontbuffer/1087 is trying to acquire lock: ffff88810dcd01a8 (&dev->master_mutex){+.+.}-{3:3}, at: drm_is_current_master+0x1b/0x40 but task is already holding lock: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&dev->mode_config.mutex){+.+.}-{3:3}: __mutex_lock+0xab/0x970 drm_client_modeset_probe+0x22e/0xca0 __drm_fb_helper_initial_config_and_unlock+0x42/0x540 intel_fbdev_initial_config+0xf/0x20 [i915] async_run_entry_fn+0x28/0x130 process_one_work+0x26d/0x5c0 worker_thread+0x37/0x380 kthread+0x144/0x170 ret_from_fork+0x1f/0x30 -> #1 (&client->modeset_mutex){+.+.}-{3:3}: __mutex_lock+0xab/0x970 drm_client_modeset_commit_locked+0x1c/0x180 drm_client_modeset_commit+0x1c/0x40 __drm_fb_helper_restore_fbdev_mode_unlocked+0x88/0xb0 drm_fb_helper_set_par+0x34/0x40 intel_fbdev_set_par+0x11/0x40 [i915] fbcon_init+0x270/0x4f0 visual_init+0xc6/0x130 do_bind_con_driver+0x1e5/0x2d0 do_take_over_console+0x10e/0x180 do_fbcon_takeover+0x53/0xb0 register_framebuffer+0x22d/0x310 __drm_fb_helper_initial_config_and_unlock+0x36c/0x540 intel_fbdev_initial_config+0xf/0x20 [i915] async_run_entry_fn+0x28/0x130 process_one_work+0x26d/0x5c0 worker_thread+0x37/0x380 kthread+0x144/0x170 ret_from_fork+0x1f/0x30 -> #0 (&dev->master_mutex){+.+.}-{3:3}: __lock_acquire+0x151e/0x2590 lock_acquire+0xd1/0x3d0 __mutex_lock+0xab/0x970 drm_is_current_master+0x1b/0x40 drm_mode_getconnector+0x37e/0x4a0 drm_ioctl_kernel+0xa8/0xf0 drm_ioctl+0x1e8/0x390 __x64_sys_ioctl+0x6a/0xa0 do_syscall_64+0x39/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: &dev->master_mutex --> &client->modeset_mutex --> &dev->mode_config.mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&dev->mode_config.mutex); lock(&client->modeset_mutex); lock(&dev->mode_config.mutex); lock(&dev->master_mutex);

drm: add a locked version of drm_is_current_master

2021-06-30T12:47:15+00:00

commit 1815d9c86e3090477fbde066ff314a7e9721ee0f upstream. While checking the master status of the DRM file in drm_is_current_master(), the device's master mutex should be held. Without the mutex, the pointer fpriv->master may be freed concurrently by another process calling drm_setmaster_ioctl(). This could lead to use-after-free errors when the pointer is subsequently dereferenced in drm_lease_owner(). The callers of drm_is_current_master() from drm_auth.c hold the device's master mutex, but external callers do not. Hence, we implement drm_is_current_master_locked() to be used within drm_auth.c, and modify drm_is_current_master() to grab the device's master mutex before checking the master status. Reported-by: Daniel Vetter Signed-off-by: Desmond Cheong Zhi Xi Reviewed-by: Emil Velikov Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210620110327.4964-2-desmondcheongzx@gmail.com Signed-off-by: Greg Kroah-Hartman

drm: Lock pointer access in drm_master_release()

2021-06-16T10:01:39+00:00

commit c336a5ee984708db4826ef9e47d184e638e29717 upstream. This patch eliminates the following smatch warning: drivers/gpu/drm/drm_auth.c:320 drm_master_release() warn: unlocked access 'master' (line 318) expected lock '&dev->master_mutex' The 'file_priv->master' field should be protected by the mutex lock to '&dev->master_mutex'. This is because other processes can concurrently modify this field and free the current 'file_priv->master' pointer. This could result in a use-after-free error when 'master' is dereferenced in subsequent function calls to 'drm_legacy_lock_master_cleanup()' or to 'drm_lease_revoke()'. An example of a scenario that would produce this error can be seen from a similar bug in 'drm_getunique()' that was reported by Syzbot: https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803 In the Syzbot report, another process concurrently acquired the device's master mutex in 'drm_setmaster_ioctl()', then overwrote 'fpriv->master' in 'drm_new_set_master()'. The old value of 'fpriv->master' was subsequently freed before the mutex was unlocked. Reported-by: Dan Carpenter Signed-off-by: Desmond Cheong Zhi Xi Cc: stable@vger.kernel.org Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210609092119.173590-1-desmondcheongzx@gmail.com Signed-off-by: Greg Kroah-Hartman

drm/auth: make drm_{set,drop}master_ioctl symmetrical

2020-06-15T13:49:50+00:00

Currently the ret handling is all over the place - with two redundant assignments and another one addressed earlier. Use the exact same flow in both functions. v2: straighten the code flow, instead of just removing the assignments Cc: David Airlie Cc: Daniel Vetter Cc: Sam Ravnborg Cc: Colin Ian King Signed-off-by: Emil Velikov Reviewed-by: Sam Ravnborg Link: https://patchwork.freedesktop.org/patch/msgid/20200530124640.4176323-2-emil.l.velikov@gmail.com

drm: vmwgfx: remove drm_driver::master_set() return type

2020-06-15T13:48:20+00:00

The function always returns zero (success). Ideally we'll remove it all together - although that's requires a little more work. For now, we can drop the return type and simplify the drm core code surrounding it. v2: remove redundant assignment (Sam) Cc: David Airlie Cc: Daniel Vetter Cc: VMware Graphics Cc: Roland Scheidegger Signed-off-by: Emil Velikov Cc: Sam Ravnborg Reviewed-by: Sam Ravnborg Reviewed-by: Roland Scheidegger Link: https://patchwork.freedesktop.org/patch/msgid/20200530124640.4176323-1-emil.l.velikov@gmail.com

drm/auth: remove redundant assignment to variable ret

2020-05-25T14:35:52+00:00

The variable ret is being initialized with a value that is never read and it is being updated later with a new value. The initialization is redundant and can be removed. Addresses-Coverity: ("Unused value") Signed-off-by: Colin Ian King Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20200524222715.27305-1-colin.king@canonical.com

drm: error out with EBUSY when device has existing master

2020-03-30T11:20:41+00:00

As requested by Adam, provide different error message for when the device has an existing master. An audit of the following projects, shows that the errno is used only for printf() purposes. xorg/xserver xorg/drivers/xf86-video-ati xorg/drivers/xf86-video-amdgpu xorg/drivers/xf86-video-intel xorg/drivers/xf86-video-tegra xorg/drivers/xf86-video-freedreno xorg/drivers/xf86-video-nouveau xorg/drivers/xf86-video-vmwgfx qt/kwin/plasma gtk/mutter/gnomeshell efl/enlightment Cc: Adam Jackson Suggested-by: Adam Jackson Signed-off-by: Emil Velikov Reviewed-by: Adam Jackson Link: https://patchwork.freedesktop.org/patch/msgid/20200319172930.230583-2-emil.l.velikov@gmail.com

drm: rework SET_MASTER and DROP_MASTER perm handling

2020-03-30T11:20:32+00:00

This commit reworks the permission handling of the two ioctls. In particular it enforced the CAP_SYS_ADMIN check only, if: - we're issuing the ioctl from process other than the one which opened the node, and - we are, or were master in the past This ensures that we: - do not regress the systemd-logind style of DRM_MASTER arbitrator - allow applications which do not use systemd-logind to drop their master capabilities (and regain them at later point) ... w/o running as root. See the comment above drm_master_check_perm() for more details. v1: - Tweak wording, fixup all checks, add igt test v2: - Add a few more comments, grammar nitpicks. Cc: Adam Jackson Cc: Daniel Vetter Cc: Pekka Paalanen Testcase: igt/core_setmaster/master-drop-set-user Signed-off-by: Emil Velikov Reviewed-by: Adam Jackson Link: https://patchwork.freedesktop.org/patch/msgid/20200319172930.230583-1-emil.l.velikov@gmail.com