pps: fix warning in pps_register_cdev when register device fail

Similar to previous commit 2a934fd ("media: v4l2-dev: fix error
handling in __video_register_device()"), the release hook should be set
before device_register(). Otherwise, when device_register() return error
and put_device() try to callback the release function, the below warning
may happen.

  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 4760 at drivers/base/core.c:2567 device_release+0x1bd/0x240 drivers/base/core.c:2567
  Modules linked in:
  CPU: 1 UID: 0 PID: 4760 Comm: syz.4.914 Not tainted 6.17.0-rc3+ #1 NONE
  RIP: 0010:device_release+0x1bd/0x240 drivers/base/core.c:2567
  Call Trace:
   <TASK>
   kobject_cleanup+0x136/0x410 lib/kobject.c:689
   kobject_release lib/kobject.c:720 [inline]
   kref_put include/linux/kref.h:65 [inline]
   kobject_put+0xe9/0x130 lib/kobject.c:737
   put_device+0x24/0x30 drivers/base/core.c:3797
   pps_register_cdev+0x2da/0x370 drivers/pps/pps.c:402
   pps_register_source+0x2f6/0x480 drivers/pps/kapi.c:108
   pps_tty_open+0x190/0x310 drivers/pps/clients/pps-ldisc.c:57
   tty_ldisc_open+0xa7/0x120 drivers/tty/tty_ldisc.c:432
   tty_set_ldisc+0x333/0x780 drivers/tty/tty_ldisc.c:563
   tiocsetd drivers/tty/tty_io.c:2429 [inline]
   tty_ioctl+0x5d1/0x1700 drivers/tty/tty_io.c:2728
   vfs_ioctl fs/ioctl.c:51 [inline]
   __do_sys_ioctl fs/ioctl.c:598 [inline]
   __se_sys_ioctl fs/ioctl.c:584 [inline]
   __x64_sys_ioctl+0x194/0x210 fs/ioctl.c:584
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0x5f/0x2a0 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x76/0x7e
   </TASK>

Before commit c79a39d ("pps: Fix a use-after-free"),
pps_register_cdev() call device_create() to create pps->dev, which will
init dev->release to device_create_release(). Now the comment is outdated,
just remove it.

Thanks for the reminder from Calvin Owens, 'kfree_pps' should be removed
in pps_register_source() to avoid a double free in the failure case.

Link: https://lore.kernel.org/all/[email protected]/
Fixes: c79a39d ("pps: Fix a use-after-free")
Signed-off-by: Wang Liang <[email protected]>
Reviewed-By: Calvin Owens <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Wang Liang

drivers/pps/kapi.c

@@ -109,16 +109,13 @@ struct pps_device *pps_register_source(struct pps_source_info *info,
 	if (err < 0) {
 		pr_err("%s: unable to create char device\n",
 					info->name);
-		goto kfree_pps;
+		goto pps_register_source_exit;
 	}
 
 	dev_dbg(&pps->dev, "new PPS source %s\n", info->name);
 
 	return pps;
 
-kfree_pps:
-	kfree(pps);
-
 pps_register_source_exit:
 	pr_err("%s: unable to register source\n", info->name);
 

drivers/pps/pps.c

@@ -374,6 +374,7 @@ int pps_register_cdev(struct pps_device *pps)
 			       pps->info.name);
 			err = -EBUSY;
 		}
+		kfree(pps);
 		goto out_unlock;
 	}
 	pps->id = err;
@@ -383,13 +384,11 @@ int pps_register_cdev(struct pps_device *pps)
 	pps->dev.devt = MKDEV(pps_major, pps->id);
 	dev_set_drvdata(&pps->dev, pps);
 	dev_set_name(&pps->dev, "pps%d", pps->id);
+	pps->dev.release = pps_device_destruct;
 	err = device_register(&pps->dev);
 	if (err)
 		goto free_idr;
 
-	/* Override the release function with our own */
-	pps->dev.release = pps_device_destruct;
-
 	pr_debug("source %s got cdev (%d:%d)\n", pps->info.name, pps_major,
 		 pps->id);