From: Eric Biggers <ebiggers@kernel.org>
To: Andrey Ryabinin <arbn@yandex-team.ru>
Cc: David Howells <dhowells@redhat.com>,
Jarkko Sakkinen <jarkko@kernel.org>,
James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
keyrings@vger.kernel.org, linux-security-module@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] keys: Allow disabling read permissions for key possessor
Date: Mon, 22 Mar 2021 17:55:29 -0700 [thread overview]
Message-ID: <YFk8gb/M4AOGDO7Y@gmail.com> (raw)
In-Reply-To: <20210322095726.14939-1-arbn@yandex-team.ru>
On Mon, Mar 22, 2021 at 12:57:26PM +0300, Andrey Ryabinin wrote:
> keyctl_read_key() has a strange code which allows possessor to read
> key's payload regardless of READ permission status:
>
> $ keyctl add user test test @u
> 196773443
> $ keyctl print 196773443
> test
> $ keyctl describe 196773443
> 196773443: alswrv-----v------------ 1000 1000 user: test
> $ keyctl rdescribe 196773443
> user;1000;1000;3f010000;test
> $ keyctl setperm 196773443 0x3d010000
> $ keyctl describe 196773443
> 196773443: alsw-v-----v------------ 1000 1000 user: test
> $ keyctl print 196773443
> test
>
> The last keyctl print should fail with -EACCESS instead of success.
> Fix this by removing weird possessor checks.
>
> Signed-off-by: Andrey Ryabinin <arbn@yandex-team.ru>
> ---
>
> - This was noticed by code review. It seems like a bug to me,
> but if I'm wrong and current behavior is correct, I think we need
> at least better comment here.
>
>
> security/keys/keyctl.c | 15 +--------------
> 1 file changed, 1 insertion(+), 14 deletions(-)
>
> diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
> index 96a92a645216d..2ec021c7adc12 100644
> --- a/security/keys/keyctl.c
> +++ b/security/keys/keyctl.c
> @@ -845,22 +845,9 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
>
> /* see if we can read it directly */
> ret = key_permission(key_ref, KEY_NEED_READ);
> - if (ret == 0)
> - goto can_read_key;
> - if (ret != -EACCES)
> + if (ret != 0)
> goto key_put_out;
>
> - /* we can't; see if it's searchable from this process's keyrings
> - * - we automatically take account of the fact that it may be
> - * dangling off an instantiation key
> - */
> - if (!is_key_possessed(key_ref)) {
> - ret = -EACCES;
> - goto key_put_out;
> - }
> -
This might be intentional, given the comment above the function:
* The key must either grant the caller Read permission, or it must grant the
* caller Search permission when searched for from the process keyrings.
The 'is_key_possessed()' check is implementing the second part, right?
Maybe check if this shows up in the documentation and tests too.
- Eric
next prev parent reply other threads:[~2021-03-23 0:56 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-22 9:57 [PATCH] keys: Allow disabling read permissions for key possessor Andrey Ryabinin
2021-03-23 0:55 ` Eric Biggers [this message]
2021-03-23 2:02 ` Jarkko Sakkinen
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