Re: [PATCH] crypto: algboss - don't wait during notifier callback
flat view
From: Eric Biggers <ebiggers@kernel.org>
Date: 2020-06-04 20:08:54
Also in:
stable
On Thu, Jun 04, 2020 at 11:52:53AM -0700, Eric Biggers wrote:
From: Eric Biggers <redacted>
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 <redacted>I forgot about the person who originally filed the bugzilla bug. Kai, if you're okay with it, let's also add: Reported-by: Kai Lüke <redacted>
quoted hunk ↗ jump to hunk
Fixes: 398710379f51 ("crypto: algapi - Move larval completion into algboss") Cc: <redacted> # v3.6+ Cc: Martin K. Petersen <redacted> Signed-off-by: Eric Biggers <redacted> --- crypto/algboss.c | 2 -- 1 file changed, 2 deletions(-)diff --git a/crypto/algboss.c b/crypto/algboss.c index 535f1f87e6c1..5ebccbd6b74e 100644 --- a/crypto/algboss.c +++ b/crypto/algboss.c@@ -178,8 +178,6 @@ 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:-- 2.27.0.rc2.251.g90737beb825-goog