From: Jeff Layton <jlayton@kernel.org>
Date: Tue, 28 Apr 2020 08:10:22 -0400
Subject: ceph: fix endianness bug when handling MDS session feature bits
Git-commit: 0fa8263367db9287aa0632f96c1a5f93cc478150
Patch-mainline: v5.7-rc5
References: bsc#1171695

Eduard reported a problem mounting cephfs on s390 arch. The feature
mask sent by the MDS is little-endian, so we need to convert it
before storing and testing against it.

Cc: stable@vger.kernel.org
Reported-and-Tested-by: Eduard Shishkin <edward6@linux.ibm.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: "Yan, Zheng" <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Acked-by: Luis Henriques <lhenriques@suse.com>
---
 fs/ceph/mds_client.c |    8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2998,8 +2998,7 @@ static void handle_session(struct ceph_m
 	void *end = p + msg->front.iov_len;
 	struct ceph_mds_session_head *h;
 	u32 op;
-	u64 seq;
-	unsigned long features = 0;
+	u64 seq, features = 0;
 	int wake = 0;
 
 	/* decode */
@@ -3017,9 +3016,8 @@ static void handle_session(struct ceph_m
 			goto bad;
 		/* version >= 3, feature bits */
 		ceph_decode_32_safe(&p, end, len, bad);
-		ceph_decode_need(&p, end, len, bad);
-		memcpy(&features, p, min_t(size_t, len, sizeof(features)));
-		p += len;
+		ceph_decode_64_safe(&p, end, features, bad);
+		p += len - sizeof(features);
 	}
 
 	mutex_lock(&mdsc->mutex);