Re: [PATCH] certs: Prevent spurious errors on repeated blacklisting
From: Mickaël Salaün
Date: Mon Nov 07 2022 - 14:40:20 EST
On 07/11/2022 17:35, Thomas Weißschuh wrote:
On 2022-11-07 17:20+0100, Mickaël Salaün wrote:
On 07/11/2022 16:55, Thomas Weißschuh wrote:
On 2022-11-07 14:12+0100, Mickaël Salaün wrote:
This is a follow-up of
https://lore.kernel.org/r/c8c65713-5cda-43ad-8018-20f2e32e4432@xxxxxxxx
Added Jarkko, Mark Pearson, Eric Snowberg and more ML in Cc.
On 04/11/2022 02:47, Thomas Weißschuh wrote:
When the blacklist keyring was changed to allow updates from the root
user it gained an ->update() function that disallows all updates.
When the a hash is blacklisted multiple times from the builtin or
firmware-provided blacklist this spams prominent logs during boot:
[ 0.890814] blacklist: Problem blacklisting hash (-13)
As all these repeated calls to mark_raw_hash_blacklisted() would create
the same keyring entry again anyways these errors can be safely ignored.
These errors can indeed be safely ignored, however they highlight issues
with some firmware vendors not checking nor optimizing their blocked hashes.
This raises security concerns, and it should be fixed by firmware vendors.
Thanks, I was not aware that these are worth fixing.
Fixes: 6364d106e041 ("certs: Allow root user to append signed hashes to the blacklist keyring")
Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx>
---
certs/blacklist.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/certs/blacklist.c b/certs/blacklist.c
index 41f10601cc72..5f7f2882ced7 100644
--- a/certs/blacklist.c
+++ b/certs/blacklist.c
@@ -191,7 +191,9 @@ static int mark_raw_hash_blacklisted(const char *hash)
BLACKLIST_KEY_PERM,
KEY_ALLOC_NOT_IN_QUOTA |
KEY_ALLOC_BUILT_IN);
- if (IS_ERR(key)) {
+
+ /* Blacklisting the same hash twice fails but would be idempotent */
+ if (IS_ERR(key) && PTR_ERR(key) != -EACCES) {
We should not hide EACCES errors. This logs issues, which is correct for
duplicate hashes, and can help firmware vendors to fix their database. I'd
really like to see a different log message instead: change the duplicate
entry error code from EACCES to EEXIST, and call pr_warn for this specific
case.
Returning EACCES would require some deeper changes to how the keyring is set up
I guess you meant EEXIST?
Indeed, sorry.
or even changes to the keyring core itself to introduce a key_create() (without
update) function.
Is this something you would take a look at, or should I try to do it?
(I have no previous knowledge about the keyring subsystem)
Please take a look. I think it should not be too complex.
Will do.
My plan is to create a new function key_create() that does takes the core logic
of key_create_or_update() and fails with EEXIST if needed.
In any case it probably would also be good to log the problematic hashes
themselves, so users can properly report the issue to their firmware vendors.
Agree
I'll send a patch for that, too.
Good!
Jarkko, David, any though?
As for this patch's Fixes-tag, it could refer to either the commit that
introduced the logging in the first place or the one that actively started to
trigger it:
* 734114f8782f ("KEYS: Add a system blacklist keyring")
* 6364d106e041 ("certs: Allow root user to append signed hashes to the blacklist keyring")
Personally I'd tend to use the latter.
Even if commit 6364d106e041 is not directly the cause of the issue, it
makes it visible, so I agree that you should keep the current Fixes tag.
pr_err("Problem blacklisting hash (%ld)\n", PTR_ERR(key));
return PTR_ERR(key);
}
base-commit: ee6050c8af96bba2f81e8b0793a1fc2f998fcd20