sunrpc: fix 4 more call sites that were using stack memory with a scatterlist

While trying to reproduce a reported kernel panic on arm64, I discovered
that AUTH_GSS basically doesn't work at all with older enctypes on arm64
systems with CONFIG_VMAP_STACK enabled.  It turns out there still a few
places using stack memory with scatterlists, causing krb5_encrypt() and
krb5_decrypt() to produce incorrect results (or a BUG if CONFIG_DEBUG_SG
is enabled).

Tested with cthon on v4.0/v4.1/v4.2 with krb5/krb5i/krb5p using
des3-cbc-sha1 and arcfour-hmac-md5.
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

net/sunrpc/auth_gss/gss_krb5_seqnum.c

@@ -44,7 +44,7 @@ krb5_make_rc4_seq_num(struct krb5_ctx *kctx, int direction, s32 seqnum,
 		      unsigned char *cksum, unsigned char *buf)
 {
 	struct crypto_sync_skcipher *cipher;
-	unsigned char plain[8];
+	unsigned char *plain;
 	s32 code;
 
 	dprintk("RPC:       %s:\n", __func__);
@@ -52,6 +52,10 @@ krb5_make_rc4_seq_num(struct krb5_ctx *kctx, int direction, s32 seqnum,
 	if (IS_ERR(cipher))
 		return PTR_ERR(cipher);
 
+	plain = kmalloc(8, GFP_NOFS);
+	if (!plain)
+		return -ENOMEM;
+
 	plain[0] = (unsigned char) ((seqnum >> 24) & 0xff);
 	plain[1] = (unsigned char) ((seqnum >> 16) & 0xff);
 	plain[2] = (unsigned char) ((seqnum >> 8) & 0xff);
@@ -67,6 +71,7 @@ krb5_make_rc4_seq_num(struct krb5_ctx *kctx, int direction, s32 seqnum,
 
 	code = krb5_encrypt(cipher, cksum, plain, buf, 8);
 out:
+	kfree(plain);
 	crypto_free_sync_skcipher(cipher);
 	return code;
 }
@@ -77,12 +82,17 @@ krb5_make_seq_num(struct krb5_ctx *kctx,
 		u32 seqnum,
 		unsigned char *cksum, unsigned char *buf)
 {
-	unsigned char plain[8];
+	unsigned char *plain;
+	s32 code;
 
 	if (kctx->enctype == ENCTYPE_ARCFOUR_HMAC)
 		return krb5_make_rc4_seq_num(kctx, direction, seqnum,
 					     cksum, buf);
 
+	plain = kmalloc(8, GFP_NOFS);
+	if (!plain)
+		return -ENOMEM;
+
 	plain[0] = (unsigned char) (seqnum & 0xff);
 	plain[1] = (unsigned char) ((seqnum >> 8) & 0xff);
 	plain[2] = (unsigned char) ((seqnum >> 16) & 0xff);
@@ -93,7 +103,9 @@ krb5_make_seq_num(struct krb5_ctx *kctx,
 	plain[6] = direction;
 	plain[7] = direction;
 
-	return krb5_encrypt(key, cksum, plain, buf, 8);
+	code = krb5_encrypt(key, cksum, plain, buf, 8);
+	kfree(plain);
+	return code;
 }
 
 static s32
@@ -101,7 +113,7 @@ krb5_get_rc4_seq_num(struct krb5_ctx *kctx, unsigned char *cksum,
 		     unsigned char *buf, int *direction, s32 *seqnum)
 {
 	struct crypto_sync_skcipher *cipher;
-	unsigned char plain[8];
+	unsigned char *plain;
 	s32 code;
 
 	dprintk("RPC:       %s:\n", __func__);
@@ -113,20 +125,28 @@ krb5_get_rc4_seq_num(struct krb5_ctx *kctx, unsigned char *cksum,
 	if (code)
 		goto out;
 
+	plain = kmalloc(8, GFP_NOFS);
+	if (!plain) {
+		code = -ENOMEM;
+		goto out;
+	}
+
 	code = krb5_decrypt(cipher, cksum, buf, plain, 8);
 	if (code)
-		goto out;
+		goto out_plain;
 
 	if ((plain[4] != plain[5]) || (plain[4] != plain[6])
 				   || (plain[4] != plain[7])) {
 		code = (s32)KG_BAD_SEQ;
-		goto out;
+		goto out_plain;
 	}
 
 	*direction = plain[4];
 
 	*seqnum = ((plain[0] << 24) | (plain[1] << 16) |
 					(plain[2] << 8) | (plain[3]));
+out_plain:
+	kfree(plain);
 out:
 	crypto_free_sync_skcipher(cipher);
 	return code;
@@ -139,7 +159,7 @@ krb5_get_seq_num(struct krb5_ctx *kctx,
 	       int *direction, u32 *seqnum)
 {
 	s32 code;
-	unsigned char plain[8];
+	unsigned char *plain;
 	struct crypto_sync_skcipher *key = kctx->seq;
 
 	dprintk("RPC:       krb5_get_seq_num:\n");
@@ -147,18 +167,25 @@ krb5_get_seq_num(struct krb5_ctx *kctx,
 	if (kctx->enctype == ENCTYPE_ARCFOUR_HMAC)
 		return krb5_get_rc4_seq_num(kctx, cksum, buf,
 					    direction, seqnum);
+	plain = kmalloc(8, GFP_NOFS);
+	if (!plain)
+		return -ENOMEM;
 
 	if ((code = krb5_decrypt(key, cksum, buf, plain, 8)))
-		return code;
+		goto out;
 
 	if ((plain[4] != plain[5]) || (plain[4] != plain[6]) ||
-	    (plain[4] != plain[7]))
-		return (s32)KG_BAD_SEQ;
+	    (plain[4] != plain[7])) {
+		code = (s32)KG_BAD_SEQ;
+		goto out;
+	}
 
 	*direction = plain[4];
 
 	*seqnum = ((plain[0]) |
 		   (plain[1] << 8) | (plain[2] << 16) | (plain[3] << 24));
 
-	return 0;
+out:
+	kfree(plain);
+	return code;
 }