Messages in this thread | | | Date | Mon, 7 Nov 2022 20:40:09 +0100 | Subject | Re: [PATCH] certs: Prevent spurious errors on repeated blacklisting | From | Mickaël Salaün <> |
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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@t-8ch.de >>>> >>>> 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@weissschuh.net> >>>>> --- >>>>> 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
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