linux-kernel - Re: [PATCH v5 02/21] xattr: define vfs_getxattr_alloc and vfs_xattr

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Date:	Wed, 18 May 2011 21:11:11 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc:	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	James Morris <jmorris@...ei.org>,
	David Safford <safford@...son.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg KH <greg@...ah.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...ia.com>,
	Mimi Zohar <zohar@...ibm.com>
Subject: Re: [PATCH v5 02/21] xattr: define vfs_getxattr_alloc and
 vfs_xattr_cmp

Quoting Mimi Zohar (zohar@...ux.vnet.ibm.com):
> vfs_getxattr_alloc() and vfs_xattr_cmp() are two new kernel xattr helper
> functions.  vfs_getxattr_alloc() first allocates memory for the requested
> xattr and then retrieves it. vfs_xattr_cmp() compares a given value with
> the contents of an extended attribute.
> 
> Signed-off-by: Mimi Zohar <zohar@...ibm.com>
> Acked-by: Serge Hallyn <serge.hallyn@...ntu.com>

Still looks good.

thanks,
-serge

> ---
>  fs/xattr.c            |   58 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/xattr.h |    5 +++-
>  2 files changed, 62 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/xattr.c b/fs/xattr.c
> index a19acdb..6da0c8c 100644
> --- a/fs/xattr.c
> +++ b/fs/xattr.c
> @@ -159,6 +159,64 @@ out_noalloc:
>  }
>  EXPORT_SYMBOL_GPL(xattr_getsecurity);
>  
> +/*
> + * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
> + *
> + * Allocate memory, if not already allocated, or re-allocate correct size,
> + * before retrieving the extended attribute.
> + *
> + * Returns the result of alloc, if failed, or the getxattr operation.
> + */
> +ssize_t
> +vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
> +		   size_t xattr_size, gfp_t flags)
> +{
> +	struct inode *inode = dentry->d_inode;
> +	char *value = *xattr_value;
> +	int error;
> +
> +	error = xattr_permission(inode, name, MAY_READ);
> +	if (error)
> +		return error;
> +
> +	if (!inode->i_op->getxattr)
> +		return -EOPNOTSUPP;
> +
> +	error = inode->i_op->getxattr(dentry, name, NULL, 0);
> +	if (error < 0)
> +		return error;
> +
> +	if (!value || (error > xattr_size)) {
> +		value = krealloc(*xattr_value, error + 1, flags);
> +		if (!value)
> +			return -ENOMEM;
> +		memset(value, 0, error + 1);
> +	}
> +
> +	error = inode->i_op->getxattr(dentry, name, value, error);
> +	*xattr_value = value;
> +	return error;
> +}
> +
> +/* Compare an extended attribute value with the given value */
> +int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
> +		  const char *value, size_t size, gfp_t flags)
> +{
> +	char *xattr_value = NULL;
> +	int rc;
> +
> +	rc = vfs_getxattr_alloc(dentry, xattr_name, &xattr_value, 0, flags);
> +	if (rc < 0)
> +		return rc;
> +
> +	if ((rc != size) || (memcmp(xattr_value, value, rc) != 0))
> +		rc = -EINVAL;
> +	else
> +		rc = 0;
> +	kfree(xattr_value);
> +	return rc;
> +}
> +
>  ssize_t
>  vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
>  {
> diff --git a/include/linux/xattr.h b/include/linux/xattr.h
> index 6050783..953a0d5 100644
> --- a/include/linux/xattr.h
> +++ b/include/linux/xattr.h
> @@ -78,7 +78,10 @@ ssize_t generic_getxattr(struct dentry *dentry, const char *name, void *buffer,
>  ssize_t generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size);
>  int generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags);
>  int generic_removexattr(struct dentry *dentry, const char *name);
> -
> +ssize_t vfs_getxattr_alloc(struct dentry *dentry, const char *name,
> +			   char **xattr_value, size_t size, gfp_t flags);
> +int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
> +		  const char *value, size_t size, gfp_t flags);
>  #endif  /*  __KERNEL__  */
>  
>  #endif	/* _LINUX_XATTR_H */
> -- 
> 1.7.3.4
> 
> --
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