linux-kernel - [PATCH V31 25/25] debugfs: Disable open() when kernel is locked down

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Date:   Tue, 26 Mar 2019 11:27:41 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, dhowells@...hat.com,
        linux-api@...r.kernel.org, luto@...nel.org,
        Matthew Garrett <mjg59@...gle.com>, gregkh@...uxfoundation.org
Subject: [PATCH V31 25/25] debugfs: Disable open() when kernel is locked down

From: Matthew Garrett <mjg59@...gle.com>

debugfs has not been meaningfully audited in terms of ensuring that
userland cannot trample over the kernel. At Greg's request, disable
access to it entirely when the kernel is locked down. This is done at
open() time rather than init time as the kernel lockdown status may be
made stricter at runtime.

Signed-off-by: Matthew Garrett <mjg59@...gle.com>
Cc: gregkh@...uxfoundation.org
---
 fs/debugfs/file.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 4fce1da7db23..9ae12ef29ba0 100644
--- 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", LOCKDOWN_INTEGRITY))
+		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", LOCKDOWN_INTEGRITY))
+		return -EPERM;
+
 	r = debugfs_file_get(dentry);
 	if (r)
 		return r == -EIO ? -ENOENT : r;
-- 
2.21.0.392.gf8f6787159e-goog