This is a note to let you know that I've just added the patch titled
KEYS: Disallow keyrings beginning with '.' to be joined as session keyrings
to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
keys-disallow-keyrings-beginning-with-.-to-be-joined-as-session-keyrings.patch
and it can be found in the queue-4.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From ee8f844e3c5a73b999edf733df1c529d6503ec2f Mon Sep 17 00:00:00 2001
From: David Howells <dhowells@xxxxxxxxxx>
Date: Tue, 18 Apr 2017 15:31:07 +0100
Subject: KEYS: Disallow keyrings beginning with '.' to be joined as session keyrings
From: David Howells <dhowells@xxxxxxxxxx>
commit ee8f844e3c5a73b999edf733df1c529d6503ec2f upstream.
This fixes CVE-2016-9604.
Keyrings whose name begin with a '.' are special internal keyrings and so
userspace isn't allowed to create keyrings by this name to prevent
shadowing. However, the patch that added the guard didn't fix
KEYCTL_JOIN_SESSION_KEYRING. Not only can that create dot-named keyrings,
it can also subscribe to them as a session keyring if they grant SEARCH
permission to the user.
This, for example, allows a root process to set .builtin_trusted_keys as
its session keyring, at which point it has full access because now the
possessor permissions are added. This permits root to add extra public
keys, thereby bypassing module verification.
This also affects kexec and IMA.
This can be tested by (as root):
keyctl session .builtin_trusted_keys
keyctl add user a a @s
keyctl list @s
which on my test box gives me:
2 keys in keyring:
180010936: ---lswrv 0 0 asymmetric: Build time autogenerated kernel key: ae3d4a31b82daa8e1a75b49dc2bba949fd992a05
801382539: --alswrv 0 0 user: a
Fix this by rejecting names beginning with a '.' in the keyctl.
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Acked-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
cc: linux-ima-devel@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
security/keys/keyctl.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -271,7 +271,8 @@ error:
* Create and join an anonymous session keyring or join a named session
* keyring, creating it if necessary. A named session keyring must have Search
* permission for it to be joined. Session keyrings without this permit will
- * be skipped over.
+ * be skipped over. It is not permitted for userspace to create or join
+ * keyrings whose name begin with a dot.
*
* If successful, the ID of the joined session keyring will be returned.
*/
@@ -288,12 +289,16 @@ long keyctl_join_session_keyring(const c
ret = PTR_ERR(name);
goto error;
}
+
+ ret = -EPERM;
+ if (name[0] == '.')
+ goto error_name;
}
/* join the session */
ret = join_session_keyring(name);
+error_name:
kfree(name);
-
error:
return ret;
}
Patches currently in stable-queue which might be from dhowells@xxxxxxxxxx are
queue-4.4/keys-disallow-keyrings-beginning-with-.-to-be-joined-as-session-keyrings.patch
queue-4.4/keys-change-the-name-of-the-dead-type-to-.dead-to-prevent-user-access.patch
queue-4.4/keys-fix-keyctl_set_reqkey_keyring-to-not-leak-thread-keyrings.patch