[PATCH v3 23/29] xattr: use posix acl api

[Christoph Hellwig]

On Wed, Sep 28, 2022 at 06:08:37PM +0200, Christian Brauner wrote:
> +static int setxattr_convert(struct user_namespace *mnt_userns, struct dentry *d,
> +			    struct xattr_ctx *ctx)
>  {
> -	if (ctx->size && is_posix_acl_xattr(ctx->kname->name))
> -		posix_acl_fix_xattr_from_user(ctx->kvalue, ctx->size);
> +	struct posix_acl *acl;
> +
> +	if (!ctx->size || !is_posix_acl_xattr(ctx->kname->name))
> +		return 0;
> +
> +	/*
> +	 * Note that posix_acl_from_xattr() uses GFP_NOFS when it probably
> +	 * doesn't need to here.
> +	 */
> +	acl = posix_acl_from_xattr(current_user_ns(), ctx->kvalue, ctx->size);
> +	if (IS_ERR(acl))
> +		return PTR_ERR(acl);
> +
> +	ctx->acl = acl;
> +	return 0;

why is this called setxattr_convert when it is clearly about ACLs only?

> +
> +	error = setxattr_convert(mnt_userns, dentry, ctx);
> +	if (error)
> +		return error;
> +
> +	if (is_posix_acl_xattr(ctx->kname->name))
> +		return vfs_set_acl(mnt_userns, dentry,
> +				   ctx->kname->name, ctx->acl);

Also instead of doing two checks for ACLs why not do just one?  And then
have a comment helper to convert and set which can live in posix_acl.c.

No need to store anything in a context with that either.

> @@ -610,6 +642,7 @@ setxattr(struct user_namespace *mnt_userns, struct dentry *d,
>  	error = do_setxattr(mnt_userns, d, &ctx);
>  
>  	kvfree(ctx.kvalue);
> +	posix_acl_release(ctx.acl);
>  	return error;

And I don't think there is any good reason to not release the ACL
right after the call to vfs_set_acl.  Which means there is no need to
store anything in the ctx.

> +	if (is_posix_acl_xattr(ctx->kname->name)) {
> +		ctx->acl = vfs_get_acl(mnt_userns, d, ctx->kname->name);
> +		if (IS_ERR(ctx->acl))
> +			return PTR_ERR(ctx->acl);
> +
> +		error = vfs_posix_acl_to_xattr(mnt_userns, d_inode(d), ctx->acl,
> +					       ctx->kvalue, ctx->size);
> +		posix_acl_release(ctx->acl);

An while this is just a small function body I still think splitting it
into a helper and moving it to posix_acl.c would be a bit cleaner.