linux-kernel - [PATCH] debugfs: lockdown: Allow reading debugfs files that are not world readable

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Date:   Tue,  4 Jan 2022 18:05:05 +0100
From:   Michal Suchanek <msuchanek@...e.de>
To:     linux-kernel@...r.kernel.org
Cc:     Michal Suchanek <msuchanek@...e.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Matthew Garrett <matthewgarrett@...gle.com>,
        James Morris <jmorris@...ei.org>,
        David Howells <dhowells@...hat.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        acpi4asus-user@...ts.sourceforge.net,
        platform-driver-x86@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>, Greg KH <greg@...ah.com>
Subject: [PATCH] debugfs: lockdown: Allow reading debugfs files that are not world readable


When the kernel is locked down the kernel allows reading only debugfs
files with mode 444. Mode 400 is also valid but is not allowed.

Make the 444 into a mask.

Fixes: 5496197f9b08 ("debugfs: Restrict debugfs when the kernel is locked down")
Signed-off-by: Michal Suchanek <msuchanek@...e.de>
---
 fs/debugfs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
index 7d162b0efbf0..950c63fa4d0b 100644
--- a/fs/debugfs/file.c
+++ b/fs/debugfs/file.c
@@ -147,7 +147,7 @@ static int debugfs_locked_down(struct inode *inode,
 			       struct file *filp,
 			       const struct file_operations *real_fops)
 {
-	if ((inode->i_mode & 07777) == 0444 &&
+	if ((inode->i_mode & 07777 & ~0444) == 0 &&
 	    !(filp->f_mode & FMODE_WRITE) &&
 	    !real_fops->unlocked_ioctl &&
 	    !real_fops->compat_ioctl &&
-- 
2.31.1