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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Mike Gerow <gerow@google.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Eric Biggers <ebiggers@google.com>,
        =?UTF-8?q?Kai=20L=C3=BCke?= <kai@kinvolk.io>,
        Herbert Xu <herbert@gondor.apana.org.au>
Subject: [PATCH 4.14 131/136] crypto: algboss - dont wait during notifier callback
Date:   Tue, 23 Jun 2020 21:59:47 +0200
Message-Id: <20200623195310.402566070@linuxfoundation.org>
In-Reply-To: <20200623195303.601828702@linuxfoundation.org>
References: <20200623195303.601828702@linuxfoundation.org>
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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(-)

--- a/crypto/algboss.c
+++ b/crypto/algboss.c
@@ -194,8 +194,6 @@ static int cryptomgr_schedule_probe(stru
 	if (IS_ERR(thread))
 		goto err_put_larval;
 
-	wait_for_completion_interruptible(&larval->completion);
-
 	return NOTIFY_STOP;
 
 err_put_larval: