KEYS: encrypted: fix race causing incorrect HMAC calculations
authorEric Biggers <ebiggers@google.com>
Thu, 8 Jun 2017 13:48:25 +0000 (14:48 +0100)
committerJames Morris <james.l.morris@oracle.com>
Fri, 9 Jun 2017 03:29:47 +0000 (13:29 +1000)
commit64d107d3acca1565c39c044c459fd18f70943534
tree3de8ea038fc4373d65160503fc039d26aa84b129
parent794b4bc292f5d31739d89c0202c54e7dc9bc3add
KEYS: encrypted: fix race causing incorrect HMAC calculations

The encrypted-keys module was using a single global HMAC transform,
which could be rekeyed by multiple threads concurrently operating on
different keys, causing incorrect HMAC values to be calculated.  Fix
this by allocating a new HMAC transform whenever we need to calculate a
HMAC.  Also simplify things a bit by allocating the shash_desc's using
SHASH_DESC_ON_STACK() for both the HMAC and unkeyed hashes.

The following script reproduces the bug:

    keyctl new_session
    keyctl add user master "abcdefghijklmnop" @s
    for i in $(seq 2); do
        (
            set -e
            for j in $(seq 1000); do
                keyid=$(keyctl add encrypted desc$i "new user:master 25" @s)
                datablob="$(keyctl pipe $keyid)"
                keyctl unlink $keyid > /dev/null
                keyid=$(keyctl add encrypted desc$i "load $datablob" @s)
                keyctl unlink $keyid > /dev/null
            done
        ) &
    done

Output with bug:

    [  439.691094] encrypted_key: bad hmac (-22)
    add_key: Invalid argument
    add_key: Invalid argument

Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
security/keys/encrypted-keys/encrypted.c