Re: [PATCH v2 08/20] afs_d_revalidate(): use stable name and parent inode passed by caller

[Al Viro <viro@zeniv.linux.org.uk>]

On Wed, Jan 22, 2025 at 09:01:24PM +0000, Al Viro wrote:
> On Wed, Jan 22, 2025 at 08:27:41PM +0000, David Howells wrote:
> > Al Viro <viro@zeniv.linux.org.uk> wrote:
> > 
> > > -	_enter("{%lu},%p{%pd},", dir->i_ino, dentry, dentry);
> > > +	_enter("{%lu},{%s},", dir->i_ino, name->name);
> > 
> > I don't think that name->name is guaranteed to be NUL-terminated after
> > name->len characters.  The following:
> > 
> > 	_enter("{%lu},{%*s},", dir->i_ino, name->len, name->name);
> > 
> > might be better, though:
> > 
> > 	_enter("{%lu},{%*.*s},", dir->i_ino, name->len, name->len, name->name);
> > 
> > might be necessary.
> 
> Good catch (and that definitely needs to be documented in previous commit),
> but what's wrong with
> 	_enter("{%lu},{%.*s},", dir->i_ino, name->len, name->name);

IOW, are you OK with the following?

commit bf61e4013ab1cb9a819303faca018e7b7cbaf3e7
Author: Al Viro <viro@zeniv.linux.org.uk>
Date:   Fri Jan 3 00:27:27 2025 -0500

    afs_d_revalidate(): use stable name and parent inode passed by caller
    
    No need to bother with boilerplate for obtaining the latter and for
    the former we really should not count upon ->d_name.name remaining
    stable under us.
    
    Reviewed-by: Jeff Layton <jlayton@kernel.org>
    Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 9780013cd83a..e04cffe4beb1 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -607,19 +607,19 @@ static bool afs_lookup_one_filldir(struct dir_context *ctx, const char *name,
  * Do a lookup of a single name in a directory
  * - just returns the FID the dentry name maps to if found
  */
-static int afs_do_lookup_one(struct inode *dir, struct dentry *dentry,
+static int afs_do_lookup_one(struct inode *dir, const struct qstr *name,
 			     struct afs_fid *fid, struct key *key,
 			     afs_dataversion_t *_dir_version)
 {
 	struct afs_super_info *as = dir->i_sb->s_fs_info;
 	struct afs_lookup_one_cookie cookie = {
 		.ctx.actor = afs_lookup_one_filldir,
-		.name = dentry->d_name,
+		.name = *name,
 		.fid.vid = as->volume->vid
 	};
 	int ret;
 
-	_enter("{%lu},%p{%pd},", dir->i_ino, dentry, dentry);
+	_enter("{%lu},{%.*s},", dir->i_ino, name->len, name->name);
 
 	/* search the directory */
 	ret = afs_dir_iterate(dir, &cookie.ctx, key, _dir_version);
@@ -1052,21 +1052,12 @@ static struct dentry *afs_lookup(struct inode *dir, struct dentry *dentry,
 /*
  * Check the validity of a dentry under RCU conditions.
  */
-static int afs_d_revalidate_rcu(struct dentry *dentry)
+static int afs_d_revalidate_rcu(struct afs_vnode *dvnode, struct dentry *dentry)
 {
-	struct afs_vnode *dvnode;
-	struct dentry *parent;
-	struct inode *dir;
 	long dir_version, de_version;
 
 	_enter("%p", dentry);
 
-	/* Check the parent directory is still valid first. */
-	parent = READ_ONCE(dentry->d_parent);
-	dir = d_inode_rcu(parent);
-	if (!dir)
-		return -ECHILD;
-	dvnode = AFS_FS_I(dir);
 	if (test_bit(AFS_VNODE_DELETED, &dvnode->flags))
 		return -ECHILD;
 
@@ -1097,9 +1088,8 @@ static int afs_d_revalidate_rcu(struct dentry *dentry)
 static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
 			    struct dentry *dentry, unsigned int flags)
 {
-	struct afs_vnode *vnode, *dir;
+	struct afs_vnode *vnode, *dir = AFS_FS_I(parent_dir);
 	struct afs_fid fid;
-	struct dentry *parent;
 	struct inode *inode;
 	struct key *key;
 	afs_dataversion_t dir_version, invalid_before;
@@ -1107,7 +1097,7 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
 	int ret;
 
 	if (flags & LOOKUP_RCU)
-		return afs_d_revalidate_rcu(dentry);
+		return afs_d_revalidate_rcu(dir, dentry);
 
 	if (d_really_is_positive(dentry)) {
 		vnode = AFS_FS_I(d_inode(dentry));
@@ -1122,14 +1112,9 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
 	if (IS_ERR(key))
 		key = NULL;
 
-	/* Hold the parent dentry so we can peer at it */
-	parent = dget_parent(dentry);
-	dir = AFS_FS_I(d_inode(parent));
-
 	/* validate the parent directory */
 	ret = afs_validate(dir, key);
 	if (ret == -ERESTARTSYS) {
-		dput(parent);
 		key_put(key);
 		return ret;
 	}
@@ -1157,7 +1142,7 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
 	afs_stat_v(dir, n_reval);
 
 	/* search the directory for this vnode */
-	ret = afs_do_lookup_one(&dir->netfs.inode, dentry, &fid, key, &dir_version);
+	ret = afs_do_lookup_one(&dir->netfs.inode, name, &fid, key, &dir_version);
 	switch (ret) {
 	case 0:
 		/* the filename maps to something */
@@ -1201,22 +1186,19 @@ static int afs_d_revalidate(struct inode *parent_dir, const struct qstr *name,
 		goto out_valid;
 
 	default:
-		_debug("failed to iterate dir %pd: %d",
-		       parent, ret);
+		_debug("failed to iterate parent %pd2: %d", dentry, ret);
 		goto not_found;
 	}
 
 out_valid:
 	dentry->d_fsdata = (void *)(unsigned long)dir_version;
 out_valid_noupdate:
-	dput(parent);
 	key_put(key);
 	_leave(" = 1 [valid]");
 	return 1;
 
 not_found:
 	_debug("dropping dentry %pd2", dentry);
-	dput(parent);
 	key_put(key);
 
 	_leave(" = 0 [bad]");