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    Subject[PATCH 4.4 069/135] crypto: algboss - don't wait during notifier callback
    Date
    From: Eric Biggers <ebiggers@google.com>

    commit 77251e41f89a813b4090f5199442f217bbf11297 upstream.

    When a crypto template needs to be instantiated, CRYPTO_MSG_ALG_REQUEST
    is sent to crypto_chain. cryptomgr_schedule_probe() handles this by
    starting a thread to instantiate the template, then waiting for this
    thread to complete via crypto_larval::completion.

    This can deadlock because instantiating the template may require loading
    modules, and this (apparently depending on userspace) may need to wait
    for the crc-t10dif module (lib/crc-t10dif.c) to be loaded. But
    crc-t10dif's module_init function uses crypto_register_notifier() and
    therefore takes crypto_chain.rwsem for write. That can't proceed until
    the notifier callback has finished, as it holds this semaphore for read.

    Fix this by removing the wait on crypto_larval::completion from within
    cryptomgr_schedule_probe(). It's actually unnecessary because
    crypto_alg_mod_lookup() calls crypto_larval_wait() itself after sending
    CRYPTO_MSG_ALG_REQUEST.

    This only actually became a problem in v4.20 due to commit b76377543b73
    ("crc-t10dif: Pick better transform if one becomes available"), but the
    unnecessary wait was much older.

    BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=207159
    Reported-by: Mike Gerow <gerow@google.com>
    Fixes: 398710379f51 ("crypto: algapi - Move larval completion into algboss")
    Cc: <stable@vger.kernel.org> # v3.6+
    Cc: Martin K. Petersen <martin.petersen@oracle.com>
    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Reported-by: Kai Lüke <kai@kinvolk.io>
    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    crypto/algboss.c | 2 --
    1 file changed, 2 deletions(-)

    diff --git a/crypto/algboss.c b/crypto/algboss.c
    index 6e39d9c05b98a..5cbc588555ca0 100644
    --- a/crypto/algboss.c
    +++ b/crypto/algboss.c
    @@ -194,8 +194,6 @@ static int cryptomgr_schedule_probe(struct crypto_larval *larval)
    if (IS_ERR(thread))
    goto err_put_larval;

    - wait_for_completion_interruptible(&larval->completion);
    -
    return NOTIFY_STOP;

    err_put_larval:
    --
    2.25.1
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