sunrpc: don't pass on-stack memory to sg_set_buf

As of ac4e97abce9b "scatterlist: sg_set_buf() argument must be in linear
mapping", sg_set_buf hits a BUG when make_checksum_v2->xdr_process_buf,
among other callers, passes it memory on the stack.

We only need a scatterlist to pass this to the crypto code, and it seems
like overkill to require kmalloc'd memory just to encrypt a few bytes,
but for now this seems the best fix.

Many of these callers are in the NFS write paths, so we allocate with
GFP_NOFS.  It might be possible to do without allocations here entirely,
but that would probably be a bigger project.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

1 files changed, 14 insertions, 7 deletions

diff --git a/net/sunrpc/auth_gss/svcauth_gss.c b/net/sunrpc/auth_gss/svcauth_gss.c
index d67f7e1bc82d..45662d7f0943 100644
--- a/net/sunrpc/auth_gss/svcauth_gss.c
+++ b/net/sunrpc/auth_gss/svcauth_gss.c
@@ -718,30 +718,37 @@ gss_write_null_verf(struct svc_rqst *rqstp)
 static int
 gss_write_verf(struct svc_rqst *rqstp, struct gss_ctx *ctx_id, u32 seq)
 {
-	__be32			xdr_seq;
+	__be32			*xdr_seq;
 	u32			maj_stat;
 	struct xdr_buf		verf_data;
 	struct xdr_netobj	mic;
 	__be32			*p;
 	struct kvec		iov;
+	int err = -1;
 
 	svc_putnl(rqstp->rq_res.head, RPC_AUTH_GSS);
-	xdr_seq = htonl(seq);
+	xdr_seq = kmalloc(4, GFP_KERNEL);
+	if (!xdr_seq)
+		return -1;
+	*xdr_seq = htonl(seq);
 
-	iov.iov_base = &xdr_seq;
-	iov.iov_len = sizeof(xdr_seq);
+	iov.iov_base = xdr_seq;
+	iov.iov_len = 4;
 	xdr_buf_from_iov(&iov, &verf_data);
 	p = rqstp->rq_res.head->iov_base + rqstp->rq_res.head->iov_len;
 	mic.data = (u8 *)(p + 1);
 	maj_stat = gss_get_mic(ctx_id, &verf_data, &mic);
 	if (maj_stat != GSS_S_COMPLETE)
-		return -1;
+		goto out;
 	*p++ = htonl(mic.len);
 	memset((u8 *)p + mic.len, 0, round_up_to_quad(mic.len) - mic.len);
 	p += XDR_QUADLEN(mic.len);
 	if (!xdr_ressize_check(rqstp, p))
-		return -1;
-	return 0;
+		goto out;
+	err = 0;
+out:
+	kfree(xdr_seq);
+	return err;
 }
 
 struct gss_domain {