linux-kernel - Re: [PATCH] tmpfs: implement generic xattr support

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Message-ID: <BANLkTinXVDrLnMOo17pqua5+38yQsezG6g@mail.gmail.com>
Date:	Wed, 20 Apr 2011 03:18:20 +0100
From:	Phillip Lougher <phillip.lougher@...il.com>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	Michal Suchanek <hramrach@...trum.cz>,
	Andreas Dilger <adilger@...ger.ca>,
	Jiri Kosina <jkosina@...e.cz>,
	Ric Wheeler <ricwheeler@...il.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Howells <dhowells@...hat.com>,
	Ian Kent <ikent@...hat.com>, Jeff Moyer <jmoyer@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, Eric Paris <eparis@...hat.com>
Subject: Re: [PATCH] tmpfs: implement generic xattr support

On Tue, Apr 19, 2011 at 9:04 PM, Miklos Szeredi <miklos@...redi.hu> wrote:

> +static ssize_t shmem_listxattr(struct dentry *dentry, char *buffer, size_t size)

> +       spin_lock(&dentry->d_inode->i_lock);
> +       list_for_each_entry(xattr, &info->xattr_list, list) {
> +               /* skip "trusted." attributes for unprivileged callers */
> +               if (!trusted && xattr_is_trusted(xattr->name))
> +                       continue;
> +
> +               used += strlen(xattr->name) + 1;
> +               if (buffer) {
> +                       if (size < used) {
> +                               used = -ERANGE;
> +                               break;
> +                       }
> +                       strncpy(buffer, xattr->name, strlen(xattr->name) + 1);
>+                        buffer += strlen(xattr->name) + 1;

Why are you doing a strncpy here?  strcpy() isn't going to copy more
than strlen(xattr->name) + 1 bytes, and you know buffer is large
enough to hold that because of the previous if (size < used) check?

If you assigned the first strlen(xattr->name) + 1 to a temporary
variable, you could use memcpy here, and avoid the 3 repeated
strlen(xattr->name) calls.

Phillip
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