[PATCH v2] drm: fix crash in drm_minor_alloc_release

[Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>]

If drm_sysfs_minor_alloc() fail in drm_minor_alloc() we can end up
freeing invalid minor->kdev pointer and drm_minor_alloc_release()
will crash like below:

RIP: 0010:kobject_put+0x19/0x1c0
RSP: 0018:ffffbc7001637c38 EFLAGS: 00010282
RAX: ffffffffa8d6deb0 RBX: 00000000ffffffff RCX: ffff9cb5912d4540
RDX: ffffffffa9c45ec5 RSI: ffff9cb5902f2b68 RDI: fffffffffffffff4
RBP: fffffffffffffff4 R08: ffffffffa9c40dec R09: 0000000000000008
R10: ffffffffaa81f7d2 R11: 00000000aa81f7ca R12: ffff9cb5912d4540
R13: ffff9cb5912d4540 R14: dead000000000122 R15: dead000000000100
FS:  00007f56b06e6740(0000) GS:ffff9cb728b40000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000030 CR3: 000000011285b004 CR4: 0000000000170ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff07f0 DR7: 0000000000000400
Call Trace:
 <TASK>
 drm_minor_alloc_release+0x19/0x50
 drm_managed_release+0xab/0x150
 drm_dev_init+0x21f/0x2f0
 __devm_drm_dev_alloc+0x3c/0xa0
 ivpu_probe+0x59/0x797 [intel_vpu 127058409b05eb2f99dcdecd3330bee28d6b3e76]
 pci_device_probe+0xa4/0x160
 really_probe+0x164/0x340
 __driver_probe_device+0x10d/0x190
 device_driver_attach+0x26/0x50
 bind_store+0x9f/0x120
 kernfs_fop_write_iter+0x12d/0x1c0
 new_sync_write+0x106/0x180
 vfs_write+0x216/0x2a0
 ksys_write+0x65/0xe0
 do_syscall_64+0x35/0x80
 entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix this crash by returning NULL minor->kdev on error.

Fixes: f96306f9892b ("drm: manage drm_minor cleanup with drmm_")
Signed-off-by: Stanislaw Gruszka <stanislaw.gruszka@linux.intel.com>
---
v2: return minor->kdev NULL pointer instead of checking for IS_ERR in
    drm_minor_alloc_release()

 drivers/gpu/drm/drm_drv.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 8214a0b1ab7f..8d70b634d008 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -142,8 +142,11 @@ static int drm_minor_alloc(struct drm_device *dev, unsigned int type)
 		return r;
 
 	minor->kdev = drm_sysfs_minor_alloc(minor);
-	if (IS_ERR(minor->kdev))
-		return PTR_ERR(minor->kdev);
+	if (IS_ERR(minor->kdev)) {
+		r = PTR_ERR(minor->kdev);
+		minor->kdev = NULL;
+		return r;
+	}
 
 	*drm_minor_get_slot(dev, type) = minor;
 	return 0;
-- 
2.25.1