debugfs: Disallow use of debugfs files when the kernel is locked down

Disallow opening of debugfs files when the kernel is locked down as various
drivers give raw access to hardware through debugfs.

Accesses to tracefs should use /sys/kernel/tracing/ rather than
/sys/kernel/debug/tracing/.  Possibly a symlink should be emplaced.

Normal device interaction should be done through configfs or a miscdev, not
debugfs.

Note that this makes it unnecessary to specifically lock down show_dsts(),
show_devs() and show_call() in the asus-wmi driver.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Andy Shevchenko <andy.shevchenko@gmail.com>
cc: acpi4asus-user@lists.sourceforge.net
cc: platform-driver-x86@vger.kernel.org
cc: Matthew Garrett <matthew.garrett@nebula.com>
cc: Thomas Gleixner <tglx@linutronix.de>
[bwh: Forward-ported to 4.15]

Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name 0024-debugfs-Disallow-use-of-debugfs-files-when-the-kerne.patch

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 1f99678ff5d3ed67d52740c8e89ab95f8e87abab..3368bfffdca2cbc97b392b2b4d1ec640961fdb0d 100644 (file)
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -142,6 +142,9 @@ static int open_proxy_open(struct inode *inode, struct file *filp)
        const struct file_operations *real_fops = NULL;
        int r;
 
+       if (kernel_is_locked_down("debugfs"))
+               return -EPERM;
+
        r = debugfs_file_get(dentry);
        if (r)
                return r == -EIO ? -ENOENT : r;
@@ -267,6 +270,9 @@ static int full_proxy_open(struct inode *inode, struct file *filp)
        struct file_operations *proxy_fops = NULL;
        int r;
 
+       if (kernel_is_locked_down("debugfs"))
+               return -EPERM;
+
        r = debugfs_file_get(dentry);
        if (r)
                return r == -EIO ? -ENOENT : r;