On Wed, 3 Jul 2019 13:31:29 -0700 Eric Biggers ebiggers@kernel.org wrote:
Hi Michal,
On Wed, Jul 03, 2019 at 10:21:08PM +0200, Michal Suchánek wrote:
On Wed, 3 Jul 2019 22:30:57 +0800 Herbert Xu herbert@gondor.apana.org.au wrote:
On Tue, Jul 02, 2019 at 02:17:00PM -0700, Eric Biggers wrote:
From: Eric Biggers ebiggers@google.com
Michal Suchanek reported [1] that running the pcrypt_aead01 test from LTP [2] in a loop and holding Ctrl-C causes a NULL dereference of alg->cra_users.next in crypto_remove_spawns(), via crypto_del_alg(). The test repeatedly uses CRYPTO_MSG_NEWALG and CRYPTO_MSG_DELALG.
The crash occurs when the instance that CRYPTO_MSG_DELALG is trying to unregister isn't a real registered algorithm, but rather is a "test larval", which is a special "algorithm" added to the algorithms list while the real algorithm is still being tested. Larvals don't have initialized cra_users, so that causes the crash. Normally pcrypt_aead01 doesn't trigger this because CRYPTO_MSG_NEWALG waits for the algorithm to be tested; however, CRYPTO_MSG_NEWALG returns early when interrupted.
Do you have some way to reproduce this reliably?
I suppose you would have to send a signal to the process for the call to get interrupted, right?
It reproduced pretty reliably for me with what you suggested. Just typing in terminal:
while true; do pcrypt_aead01; done
and then holding Ctrl-C.
If I have time I'll try writing an LTP test that specifically reproduces it. Yes, it would involve sending a signal to a thread or process that's executing CRYPTO_MSG_NEWALG (unless I find a better way).
Maybe it is possible to just send the remove message without waiting for the ack on add.
Thanks
Michal