linux-kernel - [PATCH v2 04/14] floppy: fix calling platform_device

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Date:   Mon, 27 Sep 2021 15:02:52 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     axboe@...nel.dk, efremov@...ux.com, hch@....de
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: [PATCH v2 04/14] floppy: fix calling platform_device_unregister() on invalid drives

platform_device_unregister() should only be called when
a respective platform_device_register() is called. However
the floppy driver currently allows failures when registring
a drive and a bail out could easily cause an invalid call
to platform_device_unregister() where it was not intended.

Fix this by adding a bool to keep track of when the platform
device was registered for a drive.

This does not fix any known panic / bug. This issue was found
through code inspection while preparing the driver to use the
up and coming support for device_add_disk() error handling.
>From what I can tell from code inspection, chances of this
ever happening should be insanely small, perhaps OOM.

Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---
 drivers/block/floppy.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
index 9538146e520e..3592a6277d0b 100644
--- a/drivers/block/floppy.c
+++ b/drivers/block/floppy.c
@@ -4478,6 +4478,7 @@ static const struct blk_mq_ops floppy_mq_ops = {
 };
 
 static struct platform_device floppy_device[N_DRIVE];
+static bool registered[N_DRIVE];
 
 static bool floppy_available(int drive)
 {
@@ -4693,6 +4694,8 @@ static int __init do_floppy_init(void)
 		if (err)
 			goto out_remove_drives;
 
+		registered[drive] = true;
+
 		device_add_disk(&floppy_device[drive].dev, disks[drive][0],
 				NULL);
 	}
@@ -4703,7 +4706,8 @@ static int __init do_floppy_init(void)
 	while (drive--) {
 		if (floppy_available(drive)) {
 			del_gendisk(disks[drive][0]);
-			platform_device_unregister(&floppy_device[drive]);
+			if (registered[drive])
+				platform_device_unregister(&floppy_device[drive]);
 		}
 	}
 out_release_dma:
@@ -4946,7 +4950,8 @@ static void __exit floppy_module_exit(void)
 				if (disks[drive][i])
 					del_gendisk(disks[drive][i]);
 			}
-			platform_device_unregister(&floppy_device[drive]);
+			if (registered[drive])
+				platform_device_unregister(&floppy_device[drive]);
 		}
 		for (i = 0; i < ARRAY_SIZE(floppy_type); i++) {
 			if (disks[drive][i])
-- 
2.30.2