Messages in this thread | | | From | Roman Pen <> | Subject | [RFC PATCH 0/3] debugfs: make __debugfs_remove wait for dentry release | Date | Thu, 10 Dec 2015 13:47:11 +0100 |
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Hello.
Recently I observed that all over the sources people expect that debugfs_remove() should behave as a barrier, hence file operations won't be invoked after it is called and it is safe to free remain memory.
But by default debugfs_remove() does not guarantee that dentry will be released, and after this call fops->open/read/write can still be invoked if someone holds the reference on dentry because of successfull lookup.
For example here is the grep output:
*** drivers/block/pktcdvd.c: pkt_debugfs_dev_remove[489] debugfs_remove(pd->dfs_f_info); pkt_debugfs_dev_remove[490] debugfs_remove(pd->dfs_d_root);
*** drivers/char/virtio_console.c: unplug_port[1595] debugfs_remove(port->debugfs_file);
*** drivers/crypto/qat/qat_common/adf_cfg.c: adf_cfg_dev_remove[187] debugfs_remove(dev_cfg_data->debug);
*** drivers/gpu/drm/drm_debugfs.c: drm_debugfs_remove_files[203] debugfs_remove(tmp->dent);
.... and more and more and more ...
where people do the following sequence:
debugfs_remove(dev->debugfs_dentry); kfree(dev);
and 'dev' pointer was passed to 'debugfs_create_file("my_dev", , dev, dev_fops)', so any access to 'dev' in file operations can lead to usage-after-free.
In this patch __debugfs_remove() waits for last dentry release callback.
BUT! I am not sure that nobody tries to remove the dentry from it's own file operation (dentry suicide). And if so - deadlock will happen.
Probably, dentry_remove_self() should be implemented for such cases, which is similar to sysfs_remove_file_self(). But for now I do not want to add new function which can be useless in the nearest future.
Also I did a fix for automount inodes and increased i_nlink references because of WARNING at fs/inode.c:273 drop_nlink.
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: linux-kernel@vger.kernel.org
Roman Pen (3): debugfs: fix automount inode i_nlink references debugfs: put private data to i_private for automount inode debugfs: make __debugfs_remove wait for dentry release
fs/debugfs/inode.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 51 insertions(+), 7 deletions(-)
-- 2.6.2
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