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    Subject[PATCH 3.12 46/86] KEYS: Disallow keyrings beginning with '.' to be joined as session keyrings
    Date
    From: David Howells <dhowells@redhat.com>

    3.12-stable review patch. If anyone has any objections, please let me know.

    ===============

    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: Jiri Slaby <jslaby@suse.cz>
    ---
    security/keys/keyctl.c | 9 +++++++--
    1 file changed, 7 insertions(+), 2 deletions(-)

    diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
    index 3242195bfa95..1324b2e10286 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;
    }
    --
    2.12.2
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