On Thu, Jun 04, 2020 at 11:52:53AM -0700, Eric Biggers wrote:
> From: Eric Biggers <ebiggers@xxxxxxxxxx>
>
> 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>
> ---
> crypto/algboss.c | 2 --
> 1 file changed, 2 deletions(-)
Patch applied. Thanks.
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
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