linux-kernel - Re: [PATCH] module support: during lockdown, log name of unsigned module

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Message-ID: <20200226175849.GB20449@linux-8ccs>
Date:   Wed, 26 Feb 2020 18:58:50 +0100
From:   Jessica Yu <jeyu@...nel.org>
To:     Martin Haass <vvvrrooomm@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-modules@...r.kernel.org
Subject: Re: [PATCH] module support: during lockdown, log name of unsigned
 module

+++ Martin Haass [19/02/20 10:02 +0100]:
>during lockdown loading of unsigned modules is restricted to signed
>modules only. The old error message does not show which module misses
>the signature, making it very difficult for a user to determine which
>module is at fault.
>This patch adds a line to the logs which additionally contains the
>module name that caused the error message. The old message cannot
>be replaced as it is generated by lockdown_is_locked_down
>---
> kernel/module.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
>diff --git a/kernel/module.c b/kernel/module.c
>index 33569a01d6e..6dcb28139a0 100644
>--- a/kernel/module.c
>+++ b/kernel/module.c
>@@ -2807,7 +2807,8 @@ static int module_sig_check(struct load_info *info,
>int flags)
>  const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
>  const char *reason;
>  const void *mod = info->hdr;
>-
>+ int is_locked = -EPERM;
>+
>  /*
>  * Require flags == 0, as a module with version information
>  * removed is no longer the module that was signed
>@@ -2843,7 +2844,12 @@ static int module_sig_check(struct load_info *info,
>int flags)
>  return -EKEYREJECTED;
>  }
>
>- return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
>+ is_locked = security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
>+ if (is_locked == -EPERM) {
>+ pr_notice("Lockdown: %s: rejected module '%s' cause: %s",
>+ current->comm, info->name, reason);
>+ }
>+ return is_locked;

Hi!

Actually, I think we can just reuse the pr_notice() from the previous if
(is_module_sig_enforced()) block. It already logs the module name as well as
the reason. And we'd better leave the lockdown-specific messages to the LSM.
Something like this perhaps?

diff --git a/kernel/module.c b/kernel/module.c
index b88ec9cd2a7f..2c881e3b9d92 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2838,12 +2838,13 @@ static int module_sig_check(struct load_info *info, int flags)
        case -ENOKEY:
                reason = "Loading of module with unavailable key";
        decide:
-               if (is_module_sig_enforced()) {
+               err = is_module_sig_enforced() ? \
+                     -EKEYREJECTED : security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
+
+               if (err)
                        pr_notice("%s: %s is rejected\n", info->name, reason);
-                       return -EKEYREJECTED;
-               }
 
-               return security_locked_down(LOCKDOWN_MODULE_SIGNATURE);
+               return err;
 
                /* All other errors are fatal, including nomem, unparseable
                 * signatures and signature check failures - even if signatures