Merge tag 'pull-revalidate' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs d_revalidate updates from Al Viro:
 "Provide stable parent and name to ->d_revalidate() instances

  Most of the filesystem methods where we care about dentry name and
  parent have their stability guaranteed by the callers;
  ->d_revalidate() is the major exception.

  It's easy enough for callers to supply stable values for expected name
  and expected parent of the dentry being validated. That kills quite a
  bit of boilerplate in ->d_revalidate() instances, along with a bunch
  of races where they used to access ->d_name without sufficient
  precautions"

* tag 'pull-revalidate' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  9p: fix ->rename_sem exclusion
  orangefs_d_revalidate(): use stable parent inode and name passed by caller
  ocfs2_dentry_revalidate(): use stable parent inode and name passed by caller
  nfs: fix ->d_revalidate() UAF on ->d_name accesses
  nfs{,4}_lookup_validate(): use stable parent inode passed by caller
  gfs2_drevalidate(): use stable parent inode and name passed by caller
  fuse_dentry_revalidate(): use stable parent inode and name passed by caller
  vfat_revalidate{,_ci}(): use stable parent inode passed by caller
  exfat_d_revalidate(): use stable parent inode passed by caller
  fscrypt_d_revalidate(): use stable parent inode passed by caller
  ceph_d_revalidate(): propagate stable name down into request encoding
  ceph_d_revalidate(): use stable parent inode passed by caller
  afs_d_revalidate(): use stable name and parent inode passed by caller
  Pass parent directory inode and expected name to ->d_revalidate()
  generic_ci_d_compare(): use shortname_storage
  ext4 fast_commit: make use of name_snapshot primitives
  dissolve external_name.u into separate members
  make take_dentry_name_snapshot() lockless
  dcache: back inline names with a struct-wrapped array of unsigned long
  make sure that DNAME_INLINE_LEN is a multiple of word size

3 files changed, 45 insertions, 2 deletions

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index f5e3676db954..d20a32b77b60 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -17,7 +17,8 @@ dentry_operations
 
 prototypes::
 
-	int (*d_revalidate)(struct dentry *, unsigned int);
+	int (*d_revalidate)(struct inode *, const struct qstr *,
+			    struct dentry *, unsigned int);
 	int (*d_weak_revalidate)(struct dentry *, unsigned int);
 	int (*d_hash)(const struct dentry *, struct qstr *);
 	int (*d_compare)(const struct dentry *,
@@ -30,6 +31,8 @@ prototypes::
 	struct vfsmount *(*d_automount)(struct path *path);
 	int (*d_manage)(const struct path *, bool);
 	struct dentry *(*d_real)(struct dentry *, enum d_real_type type);
+	bool (*d_unalias_trylock)(const struct dentry *);
+	void (*d_unalias_unlock)(const struct dentry *);
 
 locking rules:
 
@@ -49,6 +52,8 @@ d_dname:	   no		no		no		no
 d_automount:	   no		no		yes		no
 d_manage:	   no		no		yes (ref-walk)	maybe
 d_real		   no		no		yes 		no
+d_unalias_trylock  yes		no		no 		no
+d_unalias_unlock   yes		no		no 		no
 ================== ===========	========	==============	========
 
 inode_operations
diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index c1c121055204..1639e78e3146 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -1141,3 +1141,19 @@ pointer are gone.
 
 set_blocksize() takes opened struct file instead of struct block_device now
 and it *must* be opened exclusive.
+
+---
+
+** mandatory**
+
+->d_revalidate() gets two extra arguments - inode of parent directory and
+name our dentry is expected to have.  Both are stable (dir is pinned in
+non-RCU case and will stay around during the call in RCU case, and name
+is guaranteed to stay unchanging).  Your instance doesn't have to use
+either, but it often helps to avoid a lot of painful boilerplate.
+Note that while name->name is stable and NUL-terminated, it may (and
+often will) have name->name[name->len] equal to '/' rather than '\0' -
+in normal case it points into the pathname being looked up.
+NOTE: if you need something like full path from the root of filesystem,
+you are still on your own - this assists with simple cases, but it's not
+magic.
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 0b18af3f954e..31eea688609a 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -1251,7 +1251,8 @@ defined:
 .. code-block:: c
 
 	struct dentry_operations {
-		int (*d_revalidate)(struct dentry *, unsigned int);
+		int (*d_revalidate)(struct inode *, const struct qstr *,
+				    struct dentry *, unsigned int);
 		int (*d_weak_revalidate)(struct dentry *, unsigned int);
 		int (*d_hash)(const struct dentry *, struct qstr *);
 		int (*d_compare)(const struct dentry *,
@@ -1264,6 +1265,8 @@ defined:
 		struct vfsmount *(*d_automount)(struct path *);
 		int (*d_manage)(const struct path *, bool);
 		struct dentry *(*d_real)(struct dentry *, enum d_real_type type);
+		bool (*d_unalias_trylock)(const struct dentry *);
+		void (*d_unalias_unlock)(const struct dentry *);
 	};
 
 ``d_revalidate``
@@ -1427,6 +1430,25 @@ defined:
 
 	For non-regular files, the 'dentry' argument is returned.
 
+``d_unalias_trylock``
+	if present, will be called by d_splice_alias() before moving a
+	preexisting attached alias.  Returning false prevents __d_move(),
+	making d_splice_alias() fail with -ESTALE.
+
+	Rationale: setting FS_RENAME_DOES_D_MOVE will prevent d_move()
+	and d_exchange() calls from the outside of filesystem methods;
+	however, it does not guarantee that attached dentries won't
+	be renamed or moved by d_splice_alias() finding a preexisting
+	alias for a directory inode.  Normally we would not care;
+	however, something that wants to stabilize the entire path to
+	root over a blocking operation might need that.  See 9p for one
+	(and hopefully only) example.
+
+``d_unalias_unlock``
+	should be paired with ``d_unalias_trylock``; that one is called after
+	__d_move() call in __d_unalias().
+
+
 Each dentry has a pointer to its parent dentry, as well as a hash list
 of child dentries.  Child dentries are basically like files in a
 directory.