linux-kernel - [PATCH v2 1/1] certs: Explain the rationale to call panic()

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Date:   Tue, 22 Mar 2022 12:13:23 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Mickaël Salaün <mic@...ikod.net>,
        David Howells <dhowells@...hat.com>,
        "David S . Miller" <davem@...emloft.net>,
        David Woodhouse <dwmw2@...radead.org>,
        Eric Snowberg <eric.snowberg@...cle.com>,
        Paul Moore <paul@...l-moore.com>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Mickaël Salaün <mic@...ux.microsoft.com>
Subject: [PATCH v2 1/1] certs: Explain the rationale to call panic()

From: Mickaël Salaün <mic@...ux.microsoft.com>

The blacklist_init() function calls panic() for memory allocation
errors.  This change documents the reason why we don't return -ENODEV.

Suggested-by: Paul Moore <paul@...l-moore.com> [1]
Requested-by: Jarkko Sakkinen <jarkko@...nel.org> [1]
Link: https://lore.kernel.org/r/YjeW2r6Wv55Du0bJ@iki.fi [1]
Reviewed-by: Paul Moore <paul@...l-moore.com>
Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>
Signed-off-by: Mickaël Salaün <mic@...ux.microsoft.com>
Link: https://lore.kernel.org/r/20220322111323.542184-2-mic@digikod.net
---

Changes since v1:
* Fix commit subject spelling spotted by David Woodhouse.
* Reword one sentence as suggested by Paul Moore.
* Add Reviewed-by Paul Moore.
* Add Reviewed-by Jarkko Sakkinen.
---
 certs/blacklist.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/certs/blacklist.c b/certs/blacklist.c
index 486ce0dd8e9c..25094ea73600 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -307,6 +307,15 @@ static int restrict_link_for_blacklist(struct key *dest_keyring,
 
 /*
  * Initialise the blacklist
+ *
+ * The blacklist_init() function is registered as an initcall via
+ * device_initcall().  As a result if the blacklist_init() function fails for
+ * any reason the kernel continues to execute.  While cleanly returning -ENODEV
+ * could be acceptable for some non-critical kernel parts, if the blacklist
+ * keyring fails to load it defeats the certificate/key based deny list for
+ * signed modules.  If a critical piece of security functionality that users
+ * expect to be present fails to initialize, panic()ing is likely the right
+ * thing to do.
  */
 static int __init blacklist_init(void)
 {
-- 
2.35.1