Re: [PATCH] tmpfs: security xattr setting on inode creation

[James Morris <jmorris@namei.org>]

On Thu, 23 Feb 2012, Jarkko Sakkinen wrote:

> Adds to generic xattr support introduced in Linux 3.0 by
> implementing initxattrs callback. This enables consulting
> of security attributes from LSM and EVM when inode is
> created.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@intel.com>

Reviewed-by: James Morris <james.l.morris@oracle.com>

>  mm/shmem.c |   82 ++++++++++++++++++++++++++++++++++++++++++++++++-----------
>  1 files changed, 66 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 7a45ad0..cd367b1 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1478,6 +1478,64 @@ static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
>  }
>  
>  /*
> + * Allocate new xattr.
> + */
> +static int shmem_xattr_alloc(size_t size, struct shmem_xattr **new_xattr)
> +{
> +	/* wrap around? */
> +	size_t len = sizeof(**new_xattr) + size;
> +	if (len <= sizeof(**new_xattr))
> +		return -ENOMEM;
> +
> +	*new_xattr = kmalloc(len, GFP_KERNEL);
> +	if (*new_xattr == NULL)
> +		return -ENOMEM;
> +
> +	(*new_xattr)->size = size;
> +	return 0;
> +}
> +
> +/*
> + * Callback for security_inode_init_security() for acquiring xattrs.
> + */
> +static int shmem_initxattrs(struct inode *inode,
> +			    const struct xattr *xattr_array,
> +			    void *fs_info)
> +{
> +	const struct xattr *xattr;
> +	struct shmem_inode_info *info = SHMEM_I(inode);
> +	struct shmem_xattr *new_xattr = NULL;
> +	size_t len;
> +	int err = 0;
> +
> +	for (xattr = xattr_array; xattr->name != NULL; xattr++) {
> +		err = shmem_xattr_alloc(xattr->value_len, &new_xattr);
> +		if (err < 0)
> +			return err;
> +
> +		len = strlen(xattr->name) + 1;
> +		new_xattr->name = kmalloc(XATTR_SECURITY_PREFIX_LEN + len,
> +					  GFP_KERNEL);
> +		if (new_xattr->name == NULL) {
> +			kfree(new_xattr);
> +			return -ENOMEM;
> +		}
> +
> +		memcpy(new_xattr->name, XATTR_SECURITY_PREFIX,
> +		       XATTR_SECURITY_PREFIX_LEN);
> +		memcpy(new_xattr->name + XATTR_SECURITY_PREFIX_LEN,
> +		       xattr->name, len);
> +		memcpy(new_xattr->value, xattr->value, xattr->value_len);
> +
> +		spin_lock(&info->lock);
> +		list_add(&new_xattr->list, &info->xattr_list);
> +		spin_unlock(&info->lock);
> +	}
> +
> +	return 0;
> +}
> +
> +/*
>   * File creation. Allocate an inode, and we're done..
>   */
>  static int
> @@ -1490,7 +1548,7 @@ shmem_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
>  	if (inode) {
>  		error = security_inode_init_security(inode, dir,
>  						     &dentry->d_name,
> -						     NULL, NULL);
> +						     &shmem_initxattrs, NULL);
>  		if (error) {
>  			if (error != -EOPNOTSUPP) {
>  				iput(inode);
> @@ -1630,7 +1688,7 @@ static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *s
>  		return -ENOSPC;
>  
>  	error = security_inode_init_security(inode, dir, &dentry->d_name,
> -					     NULL, NULL);
> +					     &shmem_initxattrs, NULL);
>  	if (error) {
>  		if (error != -EOPNOTSUPP) {
>  			iput(inode);
> @@ -1731,26 +1789,19 @@ static int shmem_xattr_get(struct dentry *dentry, const char *name,
>  	return ret;
>  }
>  
> -static int shmem_xattr_set(struct dentry *dentry, const char *name,
> +static int shmem_xattr_set(struct inode *inode, const char *name,
>  			   const void *value, size_t size, int flags)
>  {
> -	struct inode *inode = dentry->d_inode;
>  	struct shmem_inode_info *info = SHMEM_I(inode);
>  	struct shmem_xattr *xattr;
>  	struct shmem_xattr *new_xattr = NULL;
> -	size_t len;
>  	int err = 0;
>  
>  	/* value == NULL means remove */
>  	if (value) {
> -		/* wrap around? */
> -		len = sizeof(*new_xattr) + size;
> -		if (len <= sizeof(*new_xattr))
> -			return -ENOMEM;
> -
> -		new_xattr = kmalloc(len, GFP_KERNEL);
> -		if (!new_xattr)
> -			return -ENOMEM;
> +		err = shmem_xattr_alloc(size, &new_xattr);
> +		if (err < 0)
> +			return err;
>  
>  		new_xattr->name = kstrdup(name, GFP_KERNEL);
>  		if (!new_xattr->name) {
> @@ -1758,7 +1809,6 @@ static int shmem_xattr_set(struct dentry *dentry, const char *name,
>  			return -ENOMEM;
>  		}
>  
> -		new_xattr->size = size;
>  		memcpy(new_xattr->value, value, size);
>  	}
>  
> @@ -1858,7 +1908,7 @@ static int shmem_setxattr(struct dentry *dentry, const char *name,
>  	if (size == 0)
>  		value = "";  /* empty EA, do not remove */
>  
> -	return shmem_xattr_set(dentry, name, value, size, flags);
> +	return shmem_xattr_set(dentry->d_inode, name, value, size, flags);
>  
>  }
>  
> @@ -1878,7 +1928,7 @@ static int shmem_removexattr(struct dentry *dentry, const char *name)
>  	if (err)
>  		return err;
>  
> -	return shmem_xattr_set(dentry, name, NULL, 0, XATTR_REPLACE);
> +	return shmem_xattr_set(dentry->d_inode, name, NULL, 0, XATTR_REPLACE);
>  }
>  
>  static bool xattr_is_trusted(const char *name)
> -- 
> 1.7.5.4
> 
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-- 
James Morris
<jmorris@namei.org>