2023-03-11 16:26:23

by Toke Høiland-Jørgensen

Subject: [PATCH] crypto: Demote BUG_ON() in crypto_unregister_alg() to a WARN_ON()

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() to WARN_ON() in
crypto_unregister_alg(). Cc stable because this problem was observed on a
6.2 kernel, cf the link below.

Link: https://lore.kernel.org/r/[email protected]
Cc: [email protected]
Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
---
crypto/algapi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/algapi.c b/crypto/algapi.c
index d08f864f08be..e9954fcb61be 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -493,7 +493,7 @@ 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);
+ WARN_ON(refcount_read(&alg->cra_refcnt) != 1);
if (alg->cra_destroy)
alg->cra_destroy(alg);

--
2.39.2

2023-03-12 07:27:31

by Herbert Xu

Subject: Re: [PATCH] crypto: Demote BUG_ON() in crypto_unregister_alg() to a WARN_ON()

On Sat, Mar 11, 2023 at 05:25:12PM +0100, Toke H?iland-J?rgensen wrote:
>
> diff --git a/crypto/algapi.c b/crypto/algapi.c
> index d08f864f08be..e9954fcb61be 100644
> --- a/crypto/algapi.c
> +++ b/crypto/algapi.c
> @@ -493,7 +493,7 @@ 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);
> + WARN_ON(refcount_read(&alg->cra_refcnt) != 1);

I think we should return here instead of continuing to destroy
the algorithm since we know that it's still in use.

Thanks,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

2023-03-12 11:10:50

by Greg Kroah-Hartman

Subject: Re: [PATCH] crypto: Demote BUG_ON() in crypto_unregister_alg() to a WARN_ON()

On Sun, Mar 12, 2023 at 03:27:10PM +0800, Herbert Xu wrote:
> On Sat, Mar 11, 2023 at 05:25:12PM +0100, Toke H?iland-J?rgensen wrote:
> >
> > diff --git a/crypto/algapi.c b/crypto/algapi.c
> > index d08f864f08be..e9954fcb61be 100644
> > --- a/crypto/algapi.c
> > +++ b/crypto/algapi.c
> > @@ -493,7 +493,7 @@ 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);
> > + WARN_ON(refcount_read(&alg->cra_refcnt) != 1);
>
> I think we should return here instead of continuing to destroy
> the algorithm since we know that it's still in use.

Also, this still panics a box with panic-on-warn enabled, so if this can
be handled, returning an error is good.

thanks,

greg k-h

2023-03-13 01:09:00

by Herbert Xu

Subject: Re: [PATCH] crypto: Demote BUG_ON() in crypto_unregister_alg() to a WARN_ON()

On Sun, Mar 12, 2023 at 12:10:38PM +0100, Greg KH wrote:
>
> Also, this still panics a box with panic-on-warn enabled, so if this can
> be handled, returning an error is good.

Well it can't really be handled because the driver is trying
to unregister an in-use algorithm so it's going to die one way
or another.

But returning here at least means that if this is happening
through shutdown then the system at least gets a chance to
reboot.

Cheers,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt