linux-kernel - [PATCH] ceph: use correct index when encoding client supported features

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Date:   Tue, 24 May 2022 17:06:27 +0100
From:   Luís Henriques <lhenriques@...e.de>
To:     Jeff Layton <jlayton@...nel.org>, Xiubo Li <xiubli@...hat.com>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Luís Henriques <lhenriques@...e.de>
Subject: [PATCH] ceph: use correct index when encoding client supported features

Feature bits have to be encoded into the correct locations.  This hasn't
been an issue so far because the only hole in the feature bits was in bit
10 (CEPHFS_FEATURE_RECLAIM_CLIENT), which is located in the 2nd byte.  When
adding more bits that go beyond the this 2nd byte, the bug will show up.

Fixes: 9ba1e224538a ("ceph: allocate the correct amount of extra bytes for the session features")
Signed-off-by: Luís Henriques <lhenriques@...e.de>
---
 fs/ceph/mds_client.c | 7 +++++--
 fs/ceph/mds_client.h | 2 --
 2 files changed, 5 insertions(+), 4 deletions(-)

I hope I got this code right.  I found this issue when trying to add an
extra feature bit that would go beyond bit 15 and that wasn't showing up
on the MDS side.

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 1bd3e1bb0fdf..77e742b6fd30 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -1220,14 +1220,17 @@ static int encode_supported_features(void **p, void *end)
 	if (count > 0) {
 		size_t i;
 		size_t size = FEATURE_BYTES(count);
+		unsigned long bit;
 
 		if (WARN_ON_ONCE(*p + 4 + size > end))
 			return -ERANGE;
 
 		ceph_encode_32(p, size);
 		memset(*p, 0, size);
-		for (i = 0; i < count; i++)
-			((unsigned char*)(*p))[i / 8] |= BIT(feature_bits[i] % 8);
+		for (i = 0; i < count; i++) {
+			bit = feature_bits[i];
+			((unsigned char *)(*p))[bit / 8] |= BIT(bit % 8);
+		}
 		*p += size;
 	} else {
 		if (WARN_ON_ONCE(*p + 4 > end))
diff --git a/fs/ceph/mds_client.h b/fs/ceph/mds_client.h
index 33497846e47e..12901e3a6823 100644
--- a/fs/ceph/mds_client.h
+++ b/fs/ceph/mds_client.h
@@ -45,8 +45,6 @@ enum ceph_feature_type {
 	CEPHFS_FEATURE_MULTI_RECONNECT,		\
 	CEPHFS_FEATURE_DELEG_INO,		\
 	CEPHFS_FEATURE_METRIC_COLLECT,		\
-						\
-	CEPHFS_FEATURE_MAX,			\
 }
 #define CEPHFS_FEATURES_CLIENT_REQUIRED {}