[PATCH v2] ceph: don't allow access to MDS-private inodes

[Jeff Layton <jlayton@kernel.org>]

The MDS reserves a set of inodes for its own usage, and these should
never be accessible to clients. Add a new helper to vet a proposed
inode number against that range, and complain loudly and refuse to
create or look it up if it's in it. We do need to carve out an exception
for the root and the lost+found directories.

Also, ensure that the MDS doesn't try to delegate that range to us
either. Print a warning if it does, and don't save the range in the
xarray.

URL: https://tracker.ceph.com/issues/49922
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Xiubo Li<xiubli@redhat.com>
Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>
---
 fs/ceph/export.c             |  8 ++++++++
 fs/ceph/inode.c              |  3 +++
 fs/ceph/mds_client.c         |  7 +++++++
 fs/ceph/super.h              | 24 ++++++++++++++++++++++++
 include/linux/ceph/ceph_fs.h |  7 ++++---
 5 files changed, 46 insertions(+), 3 deletions(-)

v2: allow lookups of lost+found dir inodes
    flesh out and update the CEPH_INO_* definitions

diff --git a/fs/ceph/export.c b/fs/ceph/export.c
index 17d8c8f4ec89..65540a4429b2 100644
--- a/fs/ceph/export.c
+++ b/fs/ceph/export.c
@@ -129,6 +129,10 @@ static struct inode *__lookup_inode(struct super_block *sb, u64 ino)
 
 	vino.ino = ino;
 	vino.snap = CEPH_NOSNAP;
+
+	if (ceph_vino_is_reserved(vino))
+		return ERR_PTR(-ESTALE);
+
 	inode = ceph_find_inode(sb, vino);
 	if (!inode) {
 		struct ceph_mds_request *req;
@@ -214,6 +218,10 @@ static struct dentry *__snapfh_to_dentry(struct super_block *sb,
 		vino.ino = sfh->ino;
 		vino.snap = sfh->snapid;
 	}
+
+	if (ceph_vino_is_reserved(vino))
+		return ERR_PTR(-ESTALE);
+
 	inode = ceph_find_inode(sb, vino);
 	if (inode)
 		return d_obtain_alias(inode);
diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
index 14a1f7963625..e1c63adb196d 100644
--- a/fs/ceph/inode.c
+++ b/fs/ceph/inode.c
@@ -56,6 +56,9 @@ struct inode *ceph_get_inode(struct super_block *sb, struct ceph_vino vino)
 {
 	struct inode *inode;
 
+	if (ceph_vino_is_reserved(vino))
+		return ERR_PTR(-EREMOTEIO);
+
 	inode = iget5_locked(sb, (unsigned long)vino.ino, ceph_ino_compare,
 			     ceph_set_ino_cb, &vino);
 	if (!inode)
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index 63b53098360c..e5af591d3bd4 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -440,6 +440,13 @@ static int ceph_parse_deleg_inos(void **p, void *end,
 
 		ceph_decode_64_safe(p, end, start, bad);
 		ceph_decode_64_safe(p, end, len, bad);
+
+		/* Don't accept a delegation of system inodes */
+		if (start < CEPH_INO_SYSTEM_BASE) {
+			pr_warn_ratelimited("ceph: ignoring reserved inode range delegation (start=0x%llx len=0x%llx)\n",
+					start, len);
+			continue;
+		}
 		while (len--) {
 			int err = xa_insert(&s->s_delegated_inos, ino = start++,
 					    DELEGATED_INO_AVAILABLE,
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index df0851b9240e..f1745403c9b0 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -529,10 +529,34 @@ static inline int ceph_ino_compare(struct inode *inode, void *data)
 		ci->i_vino.snap == pvino->snap;
 }
 
+/*
+ * The MDS reserves a set of inodes for its own usage. These should never
+ * be accessible by clients, and so the MDS has no reason to ever hand these
+ * out.
+ *
+ * These come from src/mds/mdstypes.h in the ceph sources.
+ */
+#define CEPH_MAX_MDS		0x100
+#define CEPH_NUM_STRAY		10
+#define CEPH_INO_SYSTEM_BASE	((6*CEPH_MAX_MDS) + (CEPH_MAX_MDS * CEPH_NUM_STRAY))
+
+static inline bool ceph_vino_is_reserved(const struct ceph_vino vino)
+{
+	if (vino.ino < CEPH_INO_SYSTEM_BASE &&
+	    vino.ino != CEPH_INO_ROOT &&
+	    vino.ino != CEPH_INO_LOST_AND_FOUND) {
+		WARN_RATELIMIT(1, "Attempt to access reserved inode number 0x%llx", vino.ino);
+		return true;
+	}
+	return false;
+}
 
 static inline struct inode *ceph_find_inode(struct super_block *sb,
 					    struct ceph_vino vino)
 {
+	if (ceph_vino_is_reserved(vino))
+		return NULL;
+
 	/*
 	 * NB: The hashval will be run through the fs/inode.c hash function
 	 * anyway, so there is no need to squash the inode number down to
diff --git a/include/linux/ceph/ceph_fs.h b/include/linux/ceph/ceph_fs.h
index e41a811026f6..3c90ae21a7e1 100644
--- a/include/linux/ceph/ceph_fs.h
+++ b/include/linux/ceph/ceph_fs.h
@@ -27,9 +27,10 @@
 #define CEPH_MONC_PROTOCOL   15 /* server/client */
 
 
-#define CEPH_INO_ROOT   1
-#define CEPH_INO_CEPH   2       /* hidden .ceph dir */
-#define CEPH_INO_DOTDOT 3	/* used by ceph fuse for parent (..) */
+#define CEPH_INO_ROOT			1 /* root inode number for all cephfs's */
+#define CEPH_INO_CEPH			2 /* hidden .ceph dir */
+#define CEPH_INO_GLOBAL_SNAPREALM	3 /* includes all snapshots in the fs */
+#define CEPH_INO_LOST_AND_FOUND		4 /* lost+found dir */
 
 /* arbitrary limit on max # of monitors (cluster of 3 is typical) */
 #define CEPH_MAX_MON   31
-- 
2.31.1