Clear the CRYPTO_TFM_REQ_MAY_SLEEP flag when the chacha20poly1305
operation is being continued from an async completion callback, since
sleeping may not be allowed in that context.

This is basically the same bug that was recently fixed in the xts and
lrw templates.  But, it's always been broken in chacha20poly1305 too.
This was found using syzkaller in combination with the updated crypto
self-tests which actually test the MAY_SLEEP flag now.

Reproducer:

    python -c 'import socket; socket.socket(socket.AF_ALG, 5, 0).bind(
    	       ("aead", "rfc7539(cryptd(chacha20-generic),poly1305-generic)"))'

Kernel output:

    BUG: sleeping function called from invalid context at include/crypto/algapi.h:426
    in_atomic(): 1, irqs_disabled(): 0, pid: 1001, name: kworker/2:2
    [...]
    CPU: 2 PID: 1001 Comm: kworker/2:2 Not tainted 5.2.0-rc2 #5
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-20181126_142135-anatol 04/01/2014
    Workqueue: crypto cryptd_queue_worker
    Call Trace:
     __dump_stack lib/dump_stack.c:77 [inline]
     dump_stack+0x4d/0x6a lib/dump_stack.c:113
     ___might_sleep kernel/sched/core.c:6138 [inline]
     ___might_sleep.cold.19+0x8e/0x9f kernel/sched/core.c:6095
     crypto_yield include/crypto/algapi.h:426 [inline]
     crypto_hash_walk_done+0xd6/0x100 crypto/ahash.c:113
     shash_ahash_update+0x41/0x60 crypto/shash.c:251
     shash_async_update+0xd/0x10 crypto/shash.c:260
     crypto_ahash_update include/crypto/hash.h:539 [inline]
     poly_setkey+0xf6/0x130 crypto/chacha20poly1305.c:337
     poly_init+0x51/0x60 crypto/chacha20poly1305.c:364
     async_done_continue crypto/chacha20poly1305.c:78 [inline]
     poly_genkey_done+0x15/0x30 crypto/chacha20poly1305.c:369
     cryptd_skcipher_complete+0x29/0x70 crypto/cryptd.c:279
     cryptd_skcipher_decrypt+0xcd/0x110 crypto/cryptd.c:339
     cryptd_queue_worker+0x70/0xa0 crypto/cryptd.c:184
     process_one_work+0x1ed/0x420 kernel/workqueue.c:2269
     worker_thread+0x3e/0x3a0 kernel/workqueue.c:2415
     kthread+0x11f/0x140 kernel/kthread.c:255
     ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:352

Fixes: 71ebc4d1 ("crypto: chacha20poly1305 - Add a ChaCha20-Poly1305 AEAD construction, RFC7539")
Cc: <stable@vger.kernel.org> # v4.2+
Cc: Martin Willi <martin@strongswan.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>