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SubjectRe: [PATCH] capabilities: Ambient capability set V2
On Thu, Mar 05, 2015 at 09:26:24AM -0600, Christoph Lameter wrote:
> 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?

Yes. Those are assumed to already know what they're doing.

> I think we need to keep this one.

Why? Do you foresee cases where a file that has fP set needs capabilities
that aren't in its fP?

It seems more likely that they'll risk misbehaving due to an unexpected set
of caps.

If you have a good use case I'm not entirely opposed, but it just seems
unneeded and a potentially bad idea.

> > > @@ -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@linux.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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