lkml.org 
[lkml]   [2003]   [Jun]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectFlaw in the driver-model implementation of attributes
If you're already aware of this, please forgive the intrusion.

There's a general problem in the driver model's implementation of
attribute files, in connection with loadable kernel modules. The
sysfs_ops structure stores function pointers with no means for identifying
the module that contains the corresponding code. As a result, it's
possible to call through one of these pointers even after the module has
been unloaded, causing an oops.

It's not hard to provoke this sort of situation. A user process can
open a sysfs device file, for instance, and delay trying to read it until
the module containing the device driver has been removed. When the read
does occur, it runs into trouble.

I don't know enough about the innards of the system to be able to fix this
properly. One possible approach works like this. Modify fs/sysfs/file.c
to make fill_read_buffer() and flush_write_buffer() acquire some sort of
read lock on file->f_dentry before they set attr =
file->f_dentry->d_fsdata. Modify sysfs_remove_file() to acquire a write
lock and have it set file->f_dentry->d_fsdata to NULL. Then it will only
be necessary to avoid calling ops->show() or ops->store() if attr is NULL.
This guarantees that no caller will execute the show() or store() methods
after syfs_remove_file() has returned, so a driver that cleans up after
itself correctly will not be invoked after it has been unloaded.

Alan Stern

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:36    [W:0.041 / U:5.808 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site