[PATCH 4.9 091/191] crypto: algboss - don't wait during notifier callback

[Sasha Levin]

From: Eric Biggers <ebiggers@xxxxxxxxxx>

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@xxxxxxxxxx>
Fixes: 398710379f51 ("crypto: algapi - Move larval completion into algboss")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.6+
Cc: Martin K. Petersen <martin.petersen@xxxxxxxxxx>
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
Reported-by: Kai LÃke <kai@xxxxxxxxxx>
Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 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