Pass parent directory inode and expected name to ->d_revalidate()

->d_revalidate() often needs to access dentry parent and name; that has
to be done carefully, since the locking environment varies from caller
to caller.  We are not guaranteed that dentry in question will not be
moved right under us - not unless the filesystem is such that nothing
on it ever gets renamed.

It can be dealt with, but that results in boilerplate code that isn't
even needed - the callers normally have just found the dentry via dcache
lookup and want to verify that it's in the right place; they already
have the values of ->d_parent and ->d_name stable.  There is a couple
of exceptions (overlayfs and, to less extent, ecryptfs), but for the
majority of calls that song and dance is not needed at all.

It's easier to make ecryptfs and overlayfs find and pass those values if
there's a ->d_revalidate() instance to be called, rather than doing that
in the instances.

This commit only changes the calling conventions; making use of supplied
values is left to followups.

NOTE: some instances need more than just the parent - things like CIFS
may need to build an entire path from filesystem root, so they need
more precautions than the usual boilerplate.  This series doesn't
do anything to that need - these filesystems have to keep their locking
mechanisms (rename_lock loops, use of dentry_path_raw(), private rwsem
a-la v9fs).

One thing to keep in mind when using name is that name->name will normally
point into the pathname being resolved; the filename in question occupies
name->len bytes starting at name->name, and there is NUL somewhere after it,
but it the next byte might very well be '/' rather than '\0'.  Do not
ignore name->len.

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Gabriel Krisman Bertazi <gabriel@krisman.be>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

4 files changed, 12 insertions, 6 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 0edf14a9840e..fb5493d0edf0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2058,7 +2058,8 @@ void pid_update_inode(struct task_struct *task, struct inode *inode)
  * performed a setuid(), etc.
  *
  */
-static int pid_revalidate(struct dentry *dentry, unsigned int flags)
+static int pid_revalidate(struct inode *dir, const struct qstr *name,
+			  struct dentry *dentry, unsigned int flags)
 {
 	struct inode *inode;
 	struct task_struct *task;
@@ -2191,7 +2192,8 @@ static int dname_to_vma_addr(struct dentry *dentry,
 	return 0;
 }
 
-static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
+static int map_files_d_revalidate(struct inode *dir, const struct qstr *name,
+				  struct dentry *dentry, unsigned int flags)
 {
 	unsigned long vm_start, vm_end;
 	bool exact_vma_exists = false;
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index 24baf23e864f..37aa778d1af7 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -140,7 +140,8 @@ static void tid_fd_update_inode(struct task_struct *task, struct inode *inode,
 	security_task_to_inode(task, inode);
 }
 
-static int tid_fd_revalidate(struct dentry *dentry, unsigned int flags)
+static int tid_fd_revalidate(struct inode *dir, const struct qstr *name,
+			     struct dentry *dentry, unsigned int flags)
 {
 	struct task_struct *task;
 	struct inode *inode;
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index dbe82cf23ee4..8ec90826a49e 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -216,7 +216,8 @@ void proc_free_inum(unsigned int inum)
 	ida_free(&proc_inum_ida, inum - PROC_DYNAMIC_FIRST);
 }
 
-static int proc_misc_d_revalidate(struct dentry *dentry, unsigned int flags)
+static int proc_misc_d_revalidate(struct inode *dir, const struct qstr *name,
+				  struct dentry *dentry, unsigned int flags)
 {
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;
@@ -343,7 +344,8 @@ static const struct file_operations proc_dir_operations = {
 	.iterate_shared		= proc_readdir,
 };
 
-static int proc_net_d_revalidate(struct dentry *dentry, unsigned int flags)
+static int proc_net_d_revalidate(struct inode *dir, const struct qstr *name,
+				 struct dentry *dentry, unsigned int flags)
 {
 	return 0;
 }
diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 27a283d85a6e..cc9d74a06ff0 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -884,7 +884,8 @@ static const struct inode_operations proc_sys_dir_operations = {
 	.getattr	= proc_sys_getattr,
 };
 
-static int proc_sys_revalidate(struct dentry *dentry, unsigned int flags)
+static int proc_sys_revalidate(struct inode *dir, const struct qstr *name,
+			       struct dentry *dentry, unsigned int flags)
 {
 	if (flags & LOOKUP_RCU)
 		return -ECHILD;