Hi,
I was checking debugfs code in platform/x86, because I want to add
some files to eeepc-wmi. And I found something disturbing.
The documentation says:
> This call, if successful, will make a directory called name underneath the
> indicated parent directory. If parent is NULL, the directory will be
> created in the debugfs root. On success, the return value is a struct
> dentry pointer which can be used to create files in the directory (and to
> clean it up at the end). A NULL return value indicates that something went
> wrong. If ERR_PTR(-ENODEV) is returned, that is an indication that the
> kernel has been built without debugfs support and none of the functions
> described below will work.
But then, here is the code in acer-wmi:
> static void remove_debugfs(void)
> {
> debugfs_remove(interface->debug.devices);
> debugfs_remove(interface->debug.root);
> }
>
> static int create_debugfs(void)
> {
> interface->debug.root = debugfs_create_dir("acer-wmi", NULL);
> if (!interface->debug.root) {
> printk(ACER_ERR "Failed to create debugfs directory");
> return -ENOMEM;
> }
this code is *not* inside #ifndef CONFIG_DEBUG_FS, so debugfs_create_dir
can return ERR_PTR(-ENODEV) right ?
Then, remove_debug() will call debugfs_remove(ERR_PTR(-ENODEV)) right ?
So, acpi-wmi seems to have an issue when debugfs is disabled, that's "ok".
But then I took a look at intel_ips :
> ips->debug_root = debugfs_create_dir("ips", NULL);
> if (!ips->debug_root) {
> dev_err(&ips->dev->dev,
> "failed to create debugfs entries: %ld\n",
> PTR_ERR(ips->debug_root));
> return;
> }
Then PTR_ERR thing is strange, because ips->debug_root can only be NULL
here...
But here, it's ok to only check NULL, because it's inside #ifndef
CONFIG_DEBUG_FS.
So, two drivers checked, to weird error handling code. I did a quick grep and
opened
the first result: ec_sys.c.
ec_sys.c depends on CONFIG_ACPI_EC_DEBUGFS but doesn't depend on
CONFIG_DEBUG_FS.
Here, again, the code only check for != NULL while it could be ERR_PTR(-
ENODEV):
> if (ec_device_count == 0) {
> acpi_ec_debugfs_dir = debugfs_create_dir("ec", NULL);
> if (!acpi_ec_debugfs_dir)
> return -ENOMEM;
> }
>
> sprintf(name, "ec%u", ec_device_count);
> dev_dir = debugfs_create_dir(name, acpi_ec_debugfs_dir);
Here, acpi_ec_debugfs_dir (that can be an invalid pointer) is used as
a parent dentry, and will be dereferenced without checks.
I am missing something obvious, or are most of debugfs implementation
broken when debugfs is disabled ?
Julia, if I am right, coccinelle could help us right ? Can the tool check
if the code is between #ifdef CONFIG_DEBUGS_FS ? That would help a lot.
Thanks,
--
Corentin Chary
http://xf.iksaif.net
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