[PATCH v2 57/57][X] UBUNTU: SAUCE: (efi-lockdown) debugfs: Disallow use of debugfs files when the kernel is locked down

[Seth Forshee]

From: David Howells <dhowells at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1884159

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 at redhat.com>
cc: Andy Shevchenko <andy.shevchenko at gmail.com>
cc: acpi4asus-user at lists.sourceforge.net
cc: platform-driver-x86 at vger.kernel.org
cc: Matthew Garrett <matthew.garrett at nebula.com>
cc: Thomas Gleixner <tglx at linutronix.de>
(backported from commit 125da2e1c5d0a6aca5faafba336c8e8506a4e000
 git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
---
 fs/debugfs/file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 592059f88e04..98521a791504 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -106,6 +106,9 @@ static int open_proxy_open(struct inode *inode, struct file *filp)
 	const struct file_operations *real_fops = NULL;
 	int srcu_idx, r;
 
+	if (secure_modules())
+		return -EPERM;
+
 	r = debugfs_use_file_start(dentry, &srcu_idx);
 	if (r) {
 		r = -ENOENT;
@@ -235,6 +238,9 @@ static int full_proxy_open(struct inode *inode, struct file *filp)
 	struct file_operations *proxy_fops = NULL;
 	int srcu_idx, r;
 
+	if (secure_modules())
+		return -EPERM;
+
 	r = debugfs_use_file_start(dentry, &srcu_idx);
 	if (r) {
 		r = -ENOENT;
-- 
2.27.0