linux-kernel - Re: [PATCH] LSM: Fix for security_inode

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Date:	Fri, 3 Jun 2016 23:54:31 -0500
From:	"Serge E. Hallyn" <serge@...lyn.com>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	LSM <linux-security-module@...r.kernel.org>,
	James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	LKLM <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] LSM: Fix for security_inode_getsecurity and -EOPNOTSUPP

On Tue, May 31, 2016 at 05:24:15PM -0700, Casey Schaufler wrote:
> Subject: [PATCH] LSM: Fix for security_inode_getsecurity and -EOPNOTSUPP
> 
> Serge Hallyn pointed out that the current implementation of
> security_inode_getsecurity() works if there is only one hook
> provided for it, but will fail if there is more than one and
> the attribute requested isn't supplied by the first module.
> This isn't a problem today, since only SELinux and Smack
> provide this hook and there is (currently) no way to enable
> both of those modules at the same time. Serge, however, wants
> to introduce a capability attribute and an inode_getsecurity
> hook in the capability security module to handle it. This
> addresses that upcoming problem, will be required for "extreme
> stacking" and is just a better implementation.
> 
> Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>

Thanks, Casey.

Acked-by: Serge Hallyn <serge@...lyn.com>

> ---
> 
>  security/security.c | 29 +++++++++++++++++++++++++----
>  1 file changed, 25 insertions(+), 4 deletions(-)
> 
> diff --git a/security/security.c b/security/security.c
> index 3644b03..5a749ed 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -699,18 +699,39 @@ int security_inode_killpriv(struct dentry *dentry)
>  
>  int security_inode_getsecurity(struct inode *inode, const char *name, void **buffer, bool alloc)
>  {
> +	struct security_hook_list *hp;
> +	int rc;
> +
>  	if (unlikely(IS_PRIVATE(inode)))
>  		return -EOPNOTSUPP;
> -	return call_int_hook(inode_getsecurity, -EOPNOTSUPP, inode, name,
> -				buffer, alloc);
> +	/*
> +	 * Only one module will provide an attribute with a given name.
> +	 */
> +	list_for_each_entry(hp, &security_hook_heads.inode_getsecurity, list) {
> +		rc = hp->hook.inode_getsecurity(inode, name, buffer, alloc);
> +		if (rc != -EOPNOTSUPP)
> +			return rc;
> +	}
> +	return -EOPNOTSUPP;
>  }
>  
>  int security_inode_setsecurity(struct inode *inode, const char *name, const void *value, size_t size, int flags)
>  {
> +	struct security_hook_list *hp;
> +	int rc;
> +
>  	if (unlikely(IS_PRIVATE(inode)))
>  		return -EOPNOTSUPP;
> -	return call_int_hook(inode_setsecurity, -EOPNOTSUPP, inode, name,
> -				value, size, flags);
> +	/*
> +	 * Only one module will provide an attribute with a given name.
> +	 */
> +	list_for_each_entry(hp, &security_hook_heads.inode_setsecurity, list) {
> +		rc = hp->hook.inode_setsecurity(inode, name, value, size,
> +								flags);
> +		if (rc != -EOPNOTSUPP)
> +			return rc;
> +	}
> +	return -EOPNOTSUPP;
>  }
>  
>  int security_inode_listsecurity(struct inode *inode, char *buffer, size_t buffer_size)