cryptosoft: Do not exceed crd_len around *crypt_multi

When a caller passes in a uio or mbuf chain that is longer than crd_len, in
tandem with a transform that supports the multi-block interface,
swcr_encdec() would process the entire mbuf or uio instead of just the
portion indicated by crd_len (+ crd_skip).

De/encryption are performed in-place, so this would trash subsequent uio or
mbuf contents.

This was introduced in r331639 (mea culpa).  It only affects the
{de,en}crypt_multi() family of interfaces.  That interface only has one
consumer transform in-tree (for now): Chacha20.

PR:		227605
Submitted by:	Valentin Vergez <valentin.vergez AT stormshield.eu>

sys/opencrypto/cryptosoft.c

@@ -253,7 +253,8 @@ swcr_encdec(struct cryptodesc *crd, struct swcr_data *sw, caddr_t buf,
 			size_t nb, rem;
 
 			nb = blks;
-			rem = uio->uio_iov[ind].iov_len - k;
+			rem = MIN((size_t)i,
+			    uio->uio_iov[ind].iov_len - (size_t)k);
 			idat = (uint8_t *)uio->uio_iov[ind].iov_base + k;
 
 			if (exf->reinit) {