VFS: allow ->d_manage() to declare -EISDIR in rcu_walk mode.

In REF-walk mode, ->d_manage can return -EISDIR to indicate
that the dentry is not really a mount trap (or even a mount point)
and that any mounts or any DCACHE_NEED_AUTOMOUNT flag should be
ignored.

RCU-walk mode doesn't currently support this, so if there is a dentry
with DCACHE_NEED_AUTOMOUNT set but which shouldn't be a mount-trap,
lookup_fast() will always drop in REF-walk mode.

With this patch, an -EISDIR from ->d_manage will always cause mounts
and automounts to be ignored, both in REF-walk and RCU-walk.

Bug-fixed-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 16 insertions, 11 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 0ff23cecb1bb..8a217c48f6db 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1091,10 +1091,10 @@ int follow_down_one(struct path *path)
 }
 EXPORT_SYMBOL(follow_down_one);
 
-static inline bool managed_dentry_might_block(struct dentry *dentry)
+static inline int managed_dentry_rcu(struct dentry *dentry)
 {
-        return (dentry->d_flags & DCACHE_MANAGE_TRANSIT &&
-                dentry->d_op->d_manage(dentry, true) < 0);
+        return (dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
+                dentry->d_op->d_manage(dentry, true) : 0;
 }
 
 /*
@@ -1110,11 +1110,18 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                  * Don't forget we might have a non-mountpoint managed dentry
                  * that wants to block transit.
                  */
-                if (unlikely(managed_dentry_might_block(path->dentry)))
+                switch (managed_dentry_rcu(path->dentry)) {
+                case -ECHILD:
+                default:
                         return false;
+                case -EISDIR:
+                        return true;
+                case 0:
+                        break;
+                }
 
                 if (!d_mountpoint(path->dentry))
-                        return true;
+                        return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
 
                 mounted = __lookup_mnt(path->mnt, path->dentry);
                 if (!mounted)
@@ -1130,7 +1137,8 @@ static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                  */
                 *inode = path->dentry->d_inode;
         }
-        return read_seqretry(&mount_lock, nd->m_seq);
+        return read_seqretry(&mount_lock, nd->m_seq) &&
+                !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
 }
 
 static int follow_dotdot_rcu(struct nameidata *nd)
@@ -1402,11 +1410,8 @@ static int lookup_fast(struct nameidata *nd,
                 }
                 path->mnt = mnt;
                 path->dentry = dentry;
-                if (unlikely(!__follow_mount_rcu(nd, path, inode)))
-                        goto unlazy;
-                if (unlikely(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT))
-                        goto unlazy;
-                return 0;
+                if (likely(__follow_mount_rcu(nd, path, inode)))
+                        return 0;
 unlazy:
                 if (unlazy_walk(nd, dentry))
                         return -ECHILD;