RE: [PATCH] fs: sysfs: do not remove files if group is null

[Daniel Steger <dsteger@xilinx.com>]

Hi Greg, Rafael, 

Have you had a chance to review this patch?

Thank You,
Daniel

-----Original Message-----
From: Daniel Steger <daniel.steger@xilinx.com> 
Sent: Monday, August 9, 2021 1:42 PM
To: gregkh@linuxfoundation.org; rafael@kernel.org
Cc: linux-kernel@vger.kernel.org; Daniel Steger <dsteger@xilinx.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@xilinx.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