linux-kernel - [PATCH] keys: Allow disabling read permissions for key possessor

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Date:   Mon, 22 Mar 2021 12:57:26 +0300
From:   Andrey Ryabinin <arbn@...dex-team.ru>
To:     David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko@...nel.org>
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andrey Ryabinin <arbn@...dex-team.ru>
Subject: [PATCH] keys: Allow disabling read permissions for key possessor

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@...dex-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;
-	}
-
-	/* the key is probably readable - now try to read it */
-can_read_key:
 	if (!key->type->read) {
 		ret = -EOPNOTSUPP;
 		goto key_put_out;
-- 
2.26.2