linux-kernel - Re: [PATCH] capabilities: Ambient capability set V2

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Message-ID: <alpine.DEB.2.11.1503050917380.31001@gentwo.org>
Date:	Thu, 5 Mar 2015 09:26:24 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	"Serge E. Hallyn" <serge@...lyn.com>
cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	Jonathan Corbet <corbet@....net>,
	Aaron Jones <aaronmdjones@...il.com>,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...uxfoundation.org,
	"Andrew G. Morgan" <morgan@...nel.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Austin S Hemmelgarn <ahferroin7@...il.com>,
	Markku Savela <msa@...h.iki.fi>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	linux-api@...r.kernel.org, Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH] capabilities: Ambient capability set V2

On Sun, 1 Mar 2015, Serge E. Hallyn wrote:

> > +++ linux/security/commoncap.c	2015-02-26 16:10:02.347913397 -0600
> > @@ -347,15 +347,17 @@ static inline int bprm_caps_from_vfs_cap
> >  		*has_cap = true;
> >
> >  	CAP_FOR_EACH_U32(i) {
> > +		__u32 ambient = current_cred()->cap_ambient.cap[i];
> >  		__u32 permitted = caps->permitted.cap[i];
> >  		__u32 inheritable = caps->inheritable.cap[i];
> >
> >  		/*
> > -		 * pP' = (X & fP) | (pI & fI)
> > +		 * pP' = (X & fP) | (pI & (fI | pA))
> >  		 */
> >  		new->cap_permitted.cap[i] =
> >  			(new->cap_bset.cap[i] & permitted) |
> > -			(new->cap_inheritable.cap[i] & inheritable);
> > +			(new->cap_inheritable.cap[i] &
> > +					(inheritable | ambient));
>
> So I'd say drop this change ^

Then the ambient caps get ignored for a executables that have capabilities
seton the file? I think we need to keep this one.

> > @@ -453,8 +455,18 @@ static int get_file_caps(struct linux_bi
> >  		if (rc == -EINVAL)
> >  			printk(KERN_NOTICE "%s: get_vfs_caps_from_disk returned %d for %s\n",
> >  				__func__, rc, bprm->filename);
> > -		else if (rc == -ENODATA)
> > +		else if (rc == -ENODATA) {
> >  			rc = 0;
> > +			if (!cap_isclear(current_cred()->cap_ambient)) {
> > +				/*
> > +				 * The ambient caps are permitted for
> > +				 * files that have no caps
> > +				 */
> > +				bprm->cred->cap_permitted =
> > +					current_cred()->cap_ambient;
>
> and here set vcaps inheritable to current_cred()->ambient.

We do not call bprm_caps_from_vfs_cap() for files that have no caps so
this would have no effect. But we could set cap_inheritable here?

Fixup patch:



Subject: ambient_caps: Set inheritable bits too

We were not setting the inheritable bits as they ought to be set.

Signed-off-by: Christoph Lameter <cl@...ux.com>

Index: linux/security/commoncap.c
===================================================================
--- linux.orig/security/commoncap.c	2015-03-05 09:22:32.123047869 -0600
+++ linux/security/commoncap.c	2015-03-05 09:22:32.119048001 -0600
@@ -461,6 +461,8 @@ static int get_file_caps(struct linux_bi
 				 */
 				bprm->cred->cap_permitted =
 					current_cred()->cap_ambient;
+				bprm->cred->cap_inheritable =
+					current_cred()->cap_ambient;
 				*effective = true;
 			}
 		}

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