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ceph: clean up unsafe d_parent accesses in build_dentry_path

While we hold a reference to the dentry when build_dentry_path is
called, we could end up racing with a rename that changes d_parent.
Handle that situation correctly, by using the rcu_read_lock to
ensure that the parent dentry and inode stick around long enough
to safely check ceph_snap and ceph_ino.

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>
lynxis/untested/v4.19.128
Jeff Layton 5 years ago
committed by Ilya Dryomov
parent
commit
c6b0b656ca
  1. 9
      fs/ceph/mds_client.c

9
fs/ceph/mds_client.c

@ -1800,13 +1800,18 @@ static int build_dentry_path(struct dentry *dentry,
int *pfreepath)
{
char *path;
struct inode *dir;
if (ceph_snap(d_inode(dentry->d_parent)) == CEPH_NOSNAP) {
*pino = ceph_ino(d_inode(dentry->d_parent));
rcu_read_lock();
dir = d_inode_rcu(dentry->d_parent);
if (dir && ceph_snap(dir) == CEPH_NOSNAP) {
*pino = ceph_ino(dir);
rcu_read_unlock();
*ppath = dentry->d_name.name;
*ppathlen = dentry->d_name.len;
return 0;
}
rcu_read_unlock();
path = ceph_mdsc_build_path(dentry, ppathlen, pino, 1);
if (IS_ERR(path))
return PTR_ERR(path);

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