From:   =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>
Cc:     =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= <toke@redhat.com>,
        stable@vger.kernel.org, linux-crypto@vger.kernel.org
Subject: [PATCH v2] crypto: Demote BUG_ON() in crypto_unregister_alg() to a WARN_ON()
Date:   Mon, 13 Mar 2023 10:17:24 +0100
Message-Id: <20230313091724.20941-1-toke@redhat.com>
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Precedence: bulk

The crypto_unregister_alg() function expects callers to ensure that any
algorithm that is unregistered has a refcnt of exactly 1, and issues a
BUG_ON() if this is not the case. However, there are in fact drivers that
will call crypto_unregister_alg() without ensuring that the refcnt has been
lowered first, most notably on system shutdown. This causes the BUG_ON() to
trigger, which prevents a clean shutdown and hangs the system.

To avoid such hangs on shutdown, demote the BUG_ON() in
crypto_unregister_alg() to a WARN_ON() with early return. Cc stable because
this problem was observed on a 6.2 kernel, cf the link below.

Link: https://lore.kernel.org/r/87r0tyq8ph.fsf@toke.dk
Cc: stable@vger.kernel.org
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
---
v2:
  - Return early if the WARN_ON() triggers

 crypto/algapi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/crypto/algapi.c b/crypto/algapi.c
index d08f864f08be..9de0677b3643 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -493,7 +493,9 @@ void crypto_unregister_alg(struct crypto_alg *alg)
 	if (WARN(ret, "Algorithm %s is not registered", alg->cra_driver_name))
 		return;
 
-	BUG_ON(refcount_read(&alg->cra_refcnt) != 1);
+	if (WARN_ON(refcount_read(&alg->cra_refcnt) != 1))
+		return;
+
 	if (alg->cra_destroy)
 		alg->cra_destroy(alg);
 
-- 
2.39.2