linux-kernel - Re: [PATCH] selinux: check CAP_SETFCAP for a particular inode & mapped user

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Date:   Thu, 5 Oct 2017 01:48:26 -0500
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     Lubomir Rintel <lkundrak@...sk>
Cc:     linux-security-module@...r.kernel.org,
        "Serge E . Hallyn" <serge@...lyn.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org, Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>
Subject: Re: [PATCH] selinux: check CAP_SETFCAP for a particular inode &
 mapped user

On Thu, Oct 05, 2017 at 08:16:11AM +0200, Lubomir Rintel wrote:
> This allows setting "security.capability" xattr by a user that has
> CAP_SETFCAP in an userns with SELinux. Namespaced capabilities are
> supported, as of commit 8db6c34f1dbc ("Introduce v3 namespaced file
> capabilities").
> 
> Signed-off-by: Lubomir Rintel <lkundrak@...sk>

The fix is already on its way into the kernel - see the thread at
https://marc.info/?l=selinux&m=150713903925728&w=2

Thanks though :)

-serge

> ---
> A casual warning: Please not assume I know what I'm really doing. I can now 
> install iputils and /bin/ping in a LXC container, which is great, but I 
> typically wouldn't be allowed anywhere near anything security related.
> 
> Thank you!
> 
>  security/selinux/hooks.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index f5d304736852..7bc5f4ffb4e0 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3127,11 +3127,12 @@ static int selinux_inode_getattr(const struct path *path)
>  static int selinux_inode_setotherxattr(struct dentry *dentry, const char *name)
>  {
>  	const struct cred *cred = current_cred();
> +	struct inode *inode = d_backing_inode(dentry);
>  
>  	if (!strncmp(name, XATTR_SECURITY_PREFIX,
>  		     sizeof XATTR_SECURITY_PREFIX - 1)) {
>  		if (!strcmp(name, XATTR_NAME_CAPS)) {
> -			if (!capable(CAP_SETFCAP))
> +			if (!capable_wrt_inode_uidgid(inode, CAP_SETFCAP))
>  				return -EPERM;
>  		} else if (!capable(CAP_SYS_ADMIN)) {
>  			/* A different attribute in the security namespace.
> -- 
> 2.13.6