Re: [PATCH 2/3] vfs: call audit_inode_child() in lookup_open() on failure

On Jul 10, 2026 Jori Koolstra <[email protected]> wrote:
> 
> audit_inode_child() is called in may_create_dentry() so that failed
> filesystem operations still register an audit entry. On success, the
> entry is overwritten when, for instance, fsnotify_create() is called.
> This is the calling convention in vfs_create() and vfs_mkdir().
> In lookup_open(), however, when atomic_open() should have created a
> file but didn't, no call to audit_inode_child() is made. The same is
> true for the regular ->create() path.
> 
> Fix the calling of audit_inode_child() in lookup_open() to match the
> vfs_create() path. For the ->atomic_open() filesystems this logic has
> been pushed into atomic_open(). This function is also reordered a bit
> to make the case distinction of the possible returns from
> ->atomic_open() more explicit (i.e. finish_open() or finish_no_open()).
> 
> When retrying delegation breaking, audit_inode_child() could be called
> more than once, but this is OK because those entries are reused.
> 
> Signed-off-by: Jori Koolstra <[email protected]>
> ---
>  fs/namei.c | 92 ++++++++++++++++++++++++++++++++----------------------
>  1 file changed, 55 insertions(+), 37 deletions(-)

I didn't dig into the directory lease/delegation changes because there
are better people on the To/CC line to comment on that, but the audit
changes look good to me.  Thanks for working on this, help is always
appreciated :)

Acked-by: Paul Moore (audit) <[email protected]>

> diff --git a/fs/namei.c b/fs/namei.c
> index 447eda7cbe34..fe5d59c6f925 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4351,35 +4351,55 @@ static int may_o_create(struct mnt_idmap *idmap,
>   */
>  static struct dentry *atomic_open(const struct path *path, struct dentry *dentry,
>  				  struct file *file,
> -				  int open_flag, umode_t mode)
> +				  int open_flag, umode_t mode, int create_error)
>  {
>  	struct dentry *const DENTRY_NOT_SET = (void *) -1UL;
> -	struct inode *dir =  path->dentry->d_inode;
> +	struct inode *dir_inode = path->dentry->d_inode;
>  	int error;
>  
>  	file->__f_path.dentry = DENTRY_NOT_SET;
>  	file->__f_path.mnt = path->mnt;
> -	error = dir->i_op->atomic_open(dir, dentry, file,
> +	error = dir_inode->i_op->atomic_open(dir_inode, dentry, file,
>  				       open_to_namei_flags(open_flag), mode);
>  	d_lookup_done(dentry);
> +
>  	if (!error) {
>  		if (file->f_mode & FMODE_OPENED) {
> -			if (unlikely(dentry != file->f_path.dentry)) {
> +			/* finish_open() called */
> +			struct dentry *opened = file->f_path.dentry;
> +			if (unlikely(opened != dentry)) {
>  				dput(dentry);
> -				dentry = dget(file->f_path.dentry);
> +				dentry = dget(opened);
>  			}
> -		} else if (WARN_ON(file->f_path.dentry == DENTRY_NOT_SET)) {
> -			error = -EIO;
> -		} else {
> -			if (file->f_path.dentry) {
> +		} else if (likely(file->f_path.dentry != DENTRY_NOT_SET)) {
> +			/* finish_no_open() called */
> +			struct dentry *replaced = file->f_path.dentry;
> +			if (replaced) {
>  				dput(dentry);
> -				dentry = file->f_path.dentry;
> +				dentry = replaced;
>  			}
>  			if (unlikely(d_is_negative(dentry)))
>  				error = -ENOENT;
> +		} else {
> +			const char *fsname = dentry->d_sb->s_type->name;
> +			WARN(1, "%s: ->atomic_open() left file->f_path.dentry unset!\n",
> +			        fsname);
> +			error = -EIO;
>  		}
>  	}
> +
>  	if (error) {
> +		if (unlikely(create_error) && error == -ENOENT) {
> +			/*
> +			 * Should have done a create, but errored before.
> +			 * Some filesystems return -ENOENT directly instead of
> +			 * calling finish_no_open() with a negative dentry;
> +			 * either way it should only mean the child doesn't exist,
> +			 * so a refused create is safe to record here.
> +			 */
> +			audit_inode_child(dir_inode, dentry, AUDIT_TYPE_CHILD_CREATE);
> +			error = create_error;
> +		}
>  		dput(dentry);
>  		dentry = ERR_PTR(error);
>  	}
> @@ -4437,7 +4457,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
>  		dentry = NULL;
>  	}
>  	if (dentry->d_inode) {
> -		/* Cached positive dentry: will open in f_op->open */
> +		/* Cached positive dentry: will open in do_open(). */
>  		return dentry;
>  	}
>  
> @@ -4471,10 +4491,7 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
>  	if (dir_inode->i_op->atomic_open) {
>  		if (nd->flags & LOOKUP_DIRECTORY)
>  			open_flag |= O_DIRECTORY;
> -		dentry = atomic_open(&nd->path, dentry, file, open_flag, mode);
> -		if (unlikely(create_error) && dentry == ERR_PTR(-ENOENT))
> -			dentry = ERR_PTR(create_error);
> -		return dentry;
> +		return atomic_open(&nd->path, dentry, file, open_flag, mode, create_error);
>  	}
>  
>  	if (d_in_lookup(dentry)) {
> @@ -4490,32 +4507,36 @@ static struct dentry *lookup_open(struct nameidata *nd, struct file *file,
>  			dentry = res;
>  		}
>  	}
> +	if (dentry->d_inode || !(op->open_flag & O_CREAT)) {
> +		/* No need to create a file. If lookup returned a positive
> +		 * dentry, the file will be opened in do_open(). */
> +		return dentry;
> +	}
> +
> +	/* Negative dentry with O_CREAT flag set */
> +	audit_inode_child(dir_inode, dentry, AUDIT_TYPE_CHILD_CREATE);
>  
> -	if (unlikely(create_error) && !dentry->d_inode) {
> +	if (unlikely(create_error)) {
> +		/* should have done a create, but we already errored */
>  		error = create_error;
>  		goto out_dput;
>  	}
>  
> -	/* Negative dentry, just create the file */
> -	if (!dentry->d_inode && (open_flag & O_CREAT)) {
> -		/* but break the directory lease first! */
> -		error = try_break_deleg(dir_inode, LEASE_BREAK_DIR_CREATE, delegated_inode);
> -		if (error)
> -			goto out_dput;
> -
> -		file->f_mode |= FMODE_CREATED;
> -		audit_inode_child(dir_inode, dentry, AUDIT_TYPE_CHILD_CREATE);
> -		if (!dir_inode->i_op->create) {
> -			error = -EACCES;
> -			goto out_dput;
> -		}
> +	error = try_break_deleg(dir_inode, LEASE_BREAK_DIR_CREATE, delegated_inode);
> +	if (error)
> +		goto out_dput;
>  
> -		error = dir_inode->i_op->create(idmap, dir_inode, dentry,
> -						mode, open_flag & O_EXCL);
> -		if (error)
> -			goto out_dput;
> +	file->f_mode |= FMODE_CREATED;
> +	if (!dir_inode->i_op->create) {
> +		error = -EACCES;
> +		goto out_dput;
>  	}
>  
> +	error = dir_inode->i_op->create(idmap, dir_inode, dentry,
> +					mode, open_flag & O_EXCL);
> +	if (error)
> +		goto out_dput;
> +
>  	return dentry;
>  
>  out_dput:
> @@ -5053,7 +5074,7 @@ struct file *dentry_create(struct path *path, int flags, umode_t mode,
>  
>  		/* atomic_open will dput(dentry) on error */
>  		dget(orig_dentry);
> -		dentry = atomic_open(path, dentry, file, flags, mode);
> +		dentry = atomic_open(path, dentry, file, flags, mode, create_error);
>  		error = PTR_ERR_OR_ZERO(dentry);
>  
>  		if (IS_ERR(dentry))
> @@ -5063,9 +5084,6 @@ struct file *dentry_create(struct path *path, int flags, umode_t mode,
>  			/* Drop the extra reference */
>  			dput(orig_dentry);
>  
> -		if (unlikely(create_error) && error == -ENOENT)
> -			error = create_error;
> -
>  		if (!error) {
>  			if (file->f_mode & FMODE_CREATED)
>  				fsnotify_create(dir->d_inode, dentry);
> -- 
> 2.55.0

--
paul-moore.com