linux-kernel - [PATCH] fs: sysfs: do not remove files if group is null

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Date:   Thu, 19 Aug 2021 12:10:20 -0700
From:   Daniel Steger <daniel.steger@...inx.com>
To:     <gregkh@...uxfoundation.org>, <rafael@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        Daniel Steger <daniel.steger@...inx.com>
Subject: [PATCH] fs: sysfs: do not remove files if group is null

The current implementation allows the remove_files() API to be
called without checking if the grp->name is null. Ensure that
the group name is valid prior to removing files.

This patch fixes a race condition where device_del() will cleanup
sysfs entries prior to device managed sysfs entries. This results
in a NULL group->name and a system error during device cleanup.

To reproduce the issue, simply create a new child device in a
platform driver of your choice. Add a sysfs file group using
devm API. On driver exist ensure to unregister your child device.
Do not call devm_device_remove_group() and leave it up to the
implementation to automatically clean up the files. Here is where
you will see a kernel error complaining that the files have already
been removed.

Signed-off-by: Daniel Steger <daniel.steger@...inx.com>
---
 fs/sysfs/group.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/sysfs/group.c b/fs/sysfs/group.c
index 64e6a6698935..023b40840f36 100644
--- a/fs/sysfs/group.c
+++ b/fs/sysfs/group.c
@@ -286,9 +286,10 @@ void sysfs_remove_group(struct kobject *kobj,
 		kernfs_get(kn);
 	}

-	remove_files(kn, grp);
-	if (grp->name)
+	if (grp->name) {
+		remove_files(kn, grp);
 		kernfs_remove(kn);
+	}

 	kernfs_put(kn);
 }
-- 
2.25.1