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    Subject[PATCH 4.13 59/85] lib/digsig: fix dereference of NULL user_key_payload
    Date
    4.13-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Eric Biggers <ebiggers@google.com>

    commit 192cabd6a296cbc57b3d8c05c4c89d87fc102506 upstream.

    digsig_verify() requests a user key, then accesses its payload.
    However, a revoked key has a NULL payload, and we failed to check for
    this. request_key() *does* skip revoked keys, but there is still a
    window where the key can be revoked before we acquire its semaphore.

    Fix it by checking for a NULL payload, treating it like a key which was
    already revoked at the time it was requested.

    Fixes: 051dbb918c7f ("crypto: digital signature verification support")
    Reviewed-by: James Morris <james.l.morris@oracle.com>
    Cc: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    lib/digsig.c | 6 ++++++
    1 file changed, 6 insertions(+)

    --- a/lib/digsig.c
    +++ b/lib/digsig.c
    @@ -87,6 +87,12 @@ static int digsig_verify_rsa(struct key
    down_read(&key->sem);
    ukp = user_key_payload_locked(key);

    + if (!ukp) {
    + /* key was revoked before we acquired its semaphore */
    + err = -EKEYREVOKED;
    + goto err1;
    + }
    +
    if (ukp->datalen < sizeof(*pkh))
    goto err1;


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