ceph: clean up unsafe d_parent access in __choose_mds
__choose_mds exists to pick an MDS to use when issuing a call. Doing
that typically involves picking an inode and using the authoritative
MDS for it. In most cases, that's pretty straightforward, as we are
using an inode to which we hold a reference (usually represented by
r_dentry or r_inode in the request).
In the case of a snapshotted directory however, we need to fetch
the non-snapped parent, which involves walking back up the parents
in the tree. The dentries in the snapshot dir are effectively frozen
but the overall parent is _not_, and could vanish if a concurrent
rename were to occur.
Clean this code up and take special care to ensure the validity of
the entries we're working with. First, try to use the inode in
r_locked_dir if one exists. If not and all we have is r_dentry,
then we have to walk back up the tree. Use the rcu_read_lock for
this so we can ensure that any d_parent we find won't go away, and
take extra care to deal with the possibility that the dentries could
go negative.
Change get_nonsnap_parent to return an inode, and take a reference to
that inode before returning (if any). Change all of the other places
where we set "inode" in __choose_mds to also take a reference, and then
call iput on that inode before exiting the function.
Link: http://tracker.ceph.com/issues/18148
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Yan, Zheng <zyan@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index c9d2e55..377ac34 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -668,6 +668,27 @@ static void __unregister_request(struct ceph_mds_client *mdsc,
}
/*
+ * Walk back up the dentry tree until we hit a dentry representing a
+ * non-snapshot inode. We do this using the rcu_read_lock (which must be held
+ * when calling this) to ensure that the objects won't disappear while we're
+ * working with them. Once we hit a candidate dentry, we attempt to take a
+ * reference to it, and return that as the result.
+ */
+static struct inode *get_nonsnap_parent(struct dentry *dentry) { struct inode
+ *inode = NULL;
+
+ while (dentry && !IS_ROOT(dentry)) {
+ inode = d_inode_rcu(dentry);
+ if (!inode || ceph_snap(inode) == CEPH_NOSNAP)
+ break;
+ dentry = dentry->d_parent;
+ }
+ if (inode)
+ inode = igrab(inode);
+ return inode;
+}
+
+/*
* Choose mds to send request to next. If there is a hint set in the
* request (e.g., due to a prior forward hint from the mds), use that.
* Otherwise, consult frag tree and/or caps to identify the
@@ -675,19 +696,6 @@ static void __unregister_request(struct ceph_mds_client *mdsc,
*
* Called under mdsc->mutex.
*/
-static struct dentry *get_nonsnap_parent(struct dentry *dentry)
-{
- /*
- * we don't need to worry about protecting the d_parent access
- * here because we never renaming inside the snapped namespace
- * except to resplice to another snapdir, and either the old or new
- * result is a valid result.
- */
- while (!IS_ROOT(dentry) && ceph_snap(d_inode(dentry)) != CEPH_NOSNAP)
- dentry = dentry->d_parent;
- return dentry;
-}
-
static int __choose_mds(struct ceph_mds_client *mdsc,
struct ceph_mds_request *req)
{
@@ -717,30 +725,39 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
inode = NULL;
if (req->r_inode) {
inode = req->r_inode;
+ ihold(inode);
} else if (req->r_dentry) {
/* ignore race with rename; old or new d_parent is okay */
- struct dentry *parent = req->r_dentry->d_parent;
- struct inode *dir = d_inode(parent);
+ struct dentry *parent;
+ struct inode *dir;
- if (dir->i_sb != mdsc->fsc->sb) {
- /* not this fs! */
+ rcu_read_lock();
+ parent = req->r_dentry->d_parent;
+ dir = req->r_locked_dir ? : d_inode_rcu(parent);
+
+ if (!dir || dir->i_sb != mdsc->fsc->sb) {
+ /* not this fs or parent went negative */
inode = d_inode(req->r_dentry);
+ if (inode)
+ ihold(inode);
} else if (ceph_snap(dir) != CEPH_NOSNAP) {
/* direct snapped/virtual snapdir requests
* based on parent dir inode */
- struct dentry *dn = get_nonsnap_parent(parent);
- inode = d_inode(dn);
+ inode = get_nonsnap_parent(parent);
dout("__choose_mds using nonsnap parent %p\n", inode);
} else {
/* dentry target */
inode = d_inode(req->r_dentry);
if (!inode || mode == USE_AUTH_MDS) {
/* dir + name */
- inode = dir;
+ inode = igrab(dir);
hash = ceph_dentry_hash(dir, req->r_dentry);
is_hash = true;
+ } else {
+ ihold(inode);
}
}
+ rcu_read_unlock();
}
dout("__choose_mds %p is_hash=%d (%d) mode %d\n", inode, (int)is_hash,
@@ -769,7 +786,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
(int)r, frag.ndist);
if (ceph_mdsmap_get_state(mdsc->mdsmap, mds) >=
CEPH_MDS_STATE_ACTIVE)
- return mds;
+ goto out;
}
/* since this file/dir wasn't known to be
@@ -784,7 +801,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
inode, ceph_vinop(inode), frag.frag, mds);
if (ceph_mdsmap_get_state(mdsc->mdsmap, mds) >=
CEPH_MDS_STATE_ACTIVE)
- return mds;
+ goto out;
}
}
}
@@ -797,6 +814,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
cap = rb_entry(rb_first(&ci->i_caps), struct ceph_cap, ci_node);
if (!cap) {
spin_unlock(&ci->i_ceph_lock);
+ iput(inode);
goto random;
}
mds = cap->session->s_mds;
@@ -804,6 +822,8 @@ static int __choose_mds(struct ceph_mds_client *mdsc,
inode, ceph_vinop(inode), mds,
cap == ci->i_auth_cap ? "auth " : "", cap);
spin_unlock(&ci->i_ceph_lock);
+out:
+ iput(inode);
return mds;
random:
