[SRU][F][G][PATCH 1/1] ceph: fix endianness bug when handling MDS session feature bits

[frank.heimes at canonical.com]

From: Jeff Layton <jlayton at kernel.org>

BugLink: https://bugs.launchpad.net/bugs/1875863

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 at vger.kernel.org
Reported-and-Tested-by: Eduard Shishkin <edward6 at linux.ibm.com>
Signed-off-by: Jeff Layton <jlayton at kernel.org>
Reviewed-by: "Yan, Zheng" <zyan at redhat.com>
Signed-off-by: Ilya Dryomov <idryomov at gmail.com>
(cherry picked from commit 0fa8263367db9287aa0632f96c1a5f93cc478150)
Signed-off-by: Frank Heimes <frank.heimes at canonical.com>
---
 fs/ceph/mds_client.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 8c1f04c3a684..b79fe6549df6 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -3072,8 +3072,7 @@ static void handle_session(struct ceph_mds_session *session,
 	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;
 	bool blacklisted = false;
 
@@ -3092,9 +3091,8 @@ static void handle_session(struct ceph_mds_session *session,
 			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);
-- 
2.25.1