linux-kernel - [RFC PATCH 1/6] fs: invoke LSM file_open hook in do_dentry_open for O

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Message-ID: <20250312212148.274205-2-ryan.lee@canonical.com>
Date: Wed, 12 Mar 2025 14:21:41 -0700
From: Ryan Lee <ryan.lee@...onical.com>
To: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	apparmor@...ts.ubuntu.com,
	linux-security-module@...r.kernel.org,
	selinux@...r.kernel.org
Cc: Ryan Lee <ryan.lee@...onical.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Jan Kara <jack@...e.cz>,
	John Johansen <john.johansen@...onical.com>,
	Paul Moore <paul@...l-moore.com>,
	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	Mickaël Salaün <mic@...ikod.net>,
	Günther Noack <gnoack@...gle.com>,
	Stephen Smalley <stephen.smalley.work@...il.com>,
	Ondrej Mosnacek <omosnace@...hat.com>,
	Casey Schaufler <casey@...aufler-ca.com>,
	Kentaro Takeda <takedakn@...data.co.jp>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Subject: [RFC PATCH 1/6] fs: invoke LSM file_open hook in do_dentry_open for O_PATH fds as well

Currently, opening O_PATH file descriptors completely bypasses the LSM
infrastructure. Invoking the LSM file_open hook for O_PATH fds will
be necessary for e.g. mediating the fsmount() syscall.

Signed-off-by: Ryan Lee <ryan.lee@...onical.com>
---
 fs/open.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/open.c b/fs/open.c
index 30bfcddd505d..0f8542bf6cd4 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -921,8 +921,13 @@ static int do_dentry_open(struct file *f,
 	if (unlikely(f->f_flags & O_PATH)) {
 		f->f_mode = FMODE_PATH | FMODE_OPENED;
 		file_set_fsnotify_mode(f, FMODE_NONOTIFY);
 		f->f_op = &empty_fops;
-		return 0;
+		/*
+		 * do_o_path in fs/namei.c unconditionally invokes path_put
+		 * after this function returns, so don't path_put the path
+		 * upon LSM rejection of O_PATH opening
+		 */
+		return security_file_open(f);
 	}
 
 	if ((f->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ) {
-- 
2.43.0

base-kernel: v6.14-rc6