crypto: ahash - fix another early termination in hash walk

BugLink: https://bugs.launchpad.net/bugs/1822271

commit 77568e53 upstream.

Hash algorithms with an alignmask set, e.g. "xcbc(aes-aesni)" and
"michael_mic", fail the improved hash tests because they sometimes
produce the wrong digest.  The bug is that in the case where a
scatterlist element crosses pages, not all the data is actually hashed
because the scatterlist walk terminates too early.  This happens because
the 'nbytes' variable in crypto_hash_walk_done() is assigned the number
of bytes remaining in the page, then later interpreted as the number of
bytes remaining in the scatterlist element.  Fix it.

Fixes: 900a081f ("crypto: ahash - Fix early termination in hash walk")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Juerg Haefliger <juerg.haefliger@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

crypto/ahash.c

@@ -85,17 +85,17 @@ static int hash_walk_new_entry(struct crypto_hash_walk *walk)
 int crypto_hash_walk_done(struct crypto_hash_walk *walk, int err)
 {
 	unsigned int alignmask = walk->alignmask;
-	unsigned int nbytes = walk->entrylen;
 
 	walk->data -= walk->offset;
 
-	if (nbytes && walk->offset & alignmask && !err) {
-		walk->offset = ALIGN(walk->offset, alignmask + 1);
-		nbytes = min(nbytes,
-			     ((unsigned int)(PAGE_SIZE)) - walk->offset);
-		walk->entrylen -= nbytes;
+	if (walk->entrylen && (walk->offset & alignmask) && !err) {
+		unsigned int nbytes;
 
+		walk->offset = ALIGN(walk->offset, alignmask + 1);
+		nbytes = min(walk->entrylen,
+			     (unsigned int)(PAGE_SIZE - walk->offset));
 		if (nbytes) {
+			walk->entrylen -= nbytes;
 			walk->data += walk->offset;
 			return nbytes;
 		}
@@ -115,7 +115,7 @@ int crypto_hash_walk_done(struct crypto_hash_walk *walk, int err)
 	if (err)
 		return err;
 
-	if (nbytes) {
+	if (walk->entrylen) {
 		walk->offset = 0;
 		walk->pg++;
 		return hash_walk_next(walk);