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authorDavid Howells <dhowells@redhat.com>2017-04-18 15:31:07 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-04-27 09:09:30 +0200
commitb5737b92560efcb956d2def4dcd3f4b6d4118e58 (patch)
tree95a66556ca476822f55f60d00ec6a27a785202b8
parent81af21fe95ba45261c7894b471e5d7698c4db8f1 (diff)
KEYS: Disallow keyrings beginning with '.' to be joined as session keyrings
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@redhat.com> Acked-by: Mimi Zohar <zohar@linux.vnet.ibm.com> cc: linux-ima-devel@lists.sourceforge.net Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--security/keys/keyctl.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 1c3872aeed14..4ffb51ff0a61 100644
--- 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 char __user *_name)
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;
}