linux-kernel - [PATCH 3/4] LoadPin: Move pin reporting cleanly out of locking

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Date:   Fri,  9 Dec 2022 11:57:44 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Kees Cook <keescook@...omium.org>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH 3/4] LoadPin: Move pin reporting cleanly out of locking

Refactor the pin reporting to be more cleanly outside the locking. It
was already, but moving it around helps clear the path for the root to
switch when not enforcing.

Cc: Paul Moore <paul@...l-moore.com>
Cc: James Morris <jmorris@...ei.org>
Cc: "Serge E. Hallyn" <serge@...lyn.com>
Cc: linux-security-module@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 security/loadpin/loadpin.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/security/loadpin/loadpin.c b/security/loadpin/loadpin.c
index 5b15f8f7268d..ef12d77548ae 100644
--- a/security/loadpin/loadpin.c
+++ b/security/loadpin/loadpin.c
@@ -131,6 +131,7 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 {
 	struct super_block *load_root;
 	const char *origin = kernel_read_file_id_str(id);
+	bool first_root_pin = false;
 	bool load_root_writable;
 
 	/* If the file id is excluded, ignore the pinning. */
@@ -162,18 +163,14 @@ static int loadpin_check(struct file *file, enum kernel_read_file_id id)
 	 */
 	if (!pinned_root) {
 		pinned_root = load_root;
-		/*
-		 * Unlock now since it's only pinned_root we care about.
-		 * In the worst case, we will (correctly) report pinning
-		 * failures before we have announced that pinning is
-		 * enforcing. This would be purely cosmetic.
-		 */
-		spin_unlock(&pinned_root_spinlock);
+		first_root_pin = true;
+	}
+	spin_unlock(&pinned_root_spinlock);
+
+	if (first_root_pin) {
 		report_writable(pinned_root, load_root_writable);
 		set_sysctl(load_root_writable);
 		report_load(origin, file, "pinned");
-	} else {
-		spin_unlock(&pinned_root_spinlock);
 	}
 
 	if (IS_ERR_OR_NULL(pinned_root) ||
-- 
2.34.1