ceph: decode alternate_name in lease info

Ceph is a bit different from local filesystems, in that we don't want
to store filenames as raw binary data, since we may also be dealing
with clients that don't support fscrypt.

We could just base64-encode the encrypted filenames, but that could
leave us with filenames longer than NAME_MAX. It turns out that the
MDS doesn't care much about filename length, but the clients do.

To manage this, we've added a new "alternate name" field that can be
optionally added to any dentry that we'll use to store the binary
crypttext of the filename if its base64-encoded value will be longer
than NAME_MAX. When a dentry has one of these names attached, the MDS
will send it along in the lease info, which we can then store for
later usage.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Xiubo Li <xiubli@redhat.com>
Reviewed-and-tested-by: Luís Henriques <lhenriques@suse.de>
Reviewed-by: Milind Changire <mchangir@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 33 insertions, 10 deletions

diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 126529ec7ca9..34b8c0273427 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -310,27 +310,47 @@ bad:
 
 static int parse_reply_info_lease(void **p, void *end,
 				  struct ceph_mds_reply_lease **lease,
-				  u64 features)
+				  u64 features, u32 *altname_len, u8 **altname)
 {
+	u8 struct_v;
+	u32 struct_len;
+	void *lend;
+
 	if (features == (u64)-1) {
-		u8 struct_v, struct_compat;
-		u32 struct_len;
+		u8 struct_compat;
+
 		ceph_decode_8_safe(p, end, struct_v, bad);
 		ceph_decode_8_safe(p, end, struct_compat, bad);
+
 		/* struct_v is expected to be >= 1. we only understand
 		 * encoding whose struct_compat == 1. */
 		if (!struct_v || struct_compat != 1)
 			goto bad;
+
 		ceph_decode_32_safe(p, end, struct_len, bad);
-		ceph_decode_need(p, end, struct_len, bad);
-		end = *p + struct_len;
+	} else {
+		struct_len = sizeof(**lease);
+		*altname_len = 0;
+		*altname = NULL;
 	}
 
-	ceph_decode_need(p, end, sizeof(**lease), bad);
+	lend = *p + struct_len;
+	ceph_decode_need(p, end, struct_len, bad);
 	*lease = *p;
 	*p += sizeof(**lease);
-	if (features == (u64)-1)
-		*p = end;
+
+	if (features == (u64)-1) {
+		if (struct_v >= 2) {
+			ceph_decode_32_safe(p, end, *altname_len, bad);
+			ceph_decode_need(p, end, *altname_len, bad);
+			*altname = *p;
+			*p += *altname_len;
+		} else {
+			*altname = NULL;
+			*altname_len = 0;
+		}
+	}
+	*p = lend;
 	return 0;
 bad:
 	return -EIO;
@@ -360,7 +380,8 @@ static int parse_reply_info_trace(void **p, void *end,
 		info->dname = *p;
 		*p += info->dname_len;
 
-		err = parse_reply_info_lease(p, end, &info->dlease, features);
+		err = parse_reply_info_lease(p, end, &info->dlease, features,
+					     &info->altname_len, &info->altname);
 		if (err < 0)
 			goto out_bad;
 	}
@@ -427,9 +448,11 @@ static int parse_reply_info_readdir(void **p, void *end,
 		dout("parsed dir dname '%.*s'\n", rde->name_len, rde->name);
 
 		/* dentry lease */
-		err = parse_reply_info_lease(p, end, &rde->lease, features);
+		err = parse_reply_info_lease(p, end, &rde->lease, features,
+					     &rde->altname_len, &rde->altname);
 		if (err)
 			goto out_bad;
+
 		/* inode */
 		err = parse_reply_info_in(p, end, &rde->inode, features);
 		if (err < 0)