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 <[email protected]>
Cc: [email protected]
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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