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From: "Serge E. Hallyn" <serge@hallyn.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Serge E. Hallyn" <serge@hallyn.com>,
	Linux Containers <containers@lists.linux-foundation.org>,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Andy Lutomirski <luto@amacapital.net>,
	David Howells <dhowells@redhat.com>
Subject: Re: [PATCH 3/4] userns: Add a more complete capability subset test to commit_creds
Date: Sat, 15 Dec 2012 02:06:36 +0000	[thread overview]
Message-ID: <20121215020636.GA14713@mail.hallyn.com> (raw)
In-Reply-To: <87lid0rvh9.fsf@xmission.com>

Quoting Eric W. Biederman (ebiederm@xmission.com):
> 
> When unsharing a user namespace we reduce our credentials to just what
> can be done in that user namespace.  This is a subset of the credentials
> we previously had.  Teach commit_creds to recognize this is a subset
> of the credentials we have had before and don't clear the dumpability flag.
> 
> This allows an unprivileged  program to do:
> unshare(CLONE_NEWUSER);
> fd = open("/proc/self/uid_map", O_RDWR);
> 
> Where previously opening the uid_map writable would fail because
> the the task had been made non-dumpable.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

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

> ---
>  kernel/cred.c |   27 ++++++++++++++++++++++++++-
>  1 files changed, 26 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/cred.c b/kernel/cred.c
> index 48cea3d..709d521 100644
> --- a/kernel/cred.c
> +++ b/kernel/cred.c
> @@ -455,6 +455,31 @@ error_put:
>  	return ret;
>  }
>  
> +static bool cred_cap_issubset(const struct cred *set, const struct cred *subset)
> +{
> +	const struct user_namespace *set_ns = set->user_ns;
> +	const struct user_namespace *subset_ns = subset->user_ns;
> +
> +	/* If the two credentials are in the same user namespace see if
> +	 * the capabilities of subset are a subset of set.
> +	 */
> +	if (set_ns == subset_ns)
> +		return cap_issubset(subset->cap_permitted, set->cap_permitted);
> +
> +	/* The credentials are in a different user namespaces
> +	 * therefore one is a subset of the other only if a set is an
> +	 * ancestor of subset and set->euid is owner of subset or one
> +	 * of subsets ancestors.
> +	 */
> +	for (;subset_ns != &init_user_ns; subset_ns = subset_ns->parent) {
> +		if ((set_ns == subset_ns->parent)  &&
> +		    uid_eq(subset_ns->owner, set->euid))
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  /**
>   * commit_creds - Install new credentials upon the current task
>   * @new: The credentials to be assigned
> @@ -493,7 +518,7 @@ int commit_creds(struct cred *new)
>  	    !gid_eq(old->egid, new->egid) ||
>  	    !uid_eq(old->fsuid, new->fsuid) ||
>  	    !gid_eq(old->fsgid, new->fsgid) ||
> -	    !cap_issubset(new->cap_permitted, old->cap_permitted)) {
> +	    !cred_cap_issubset(old, new)) {
>  		if (task->mm)
>  			set_dumpable(task->mm, suid_dumpable);
>  		task->pdeath_signal = 0;
> -- 
> 1.7.5.4

  reply	other threads:[~2012-12-15  2:01 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-12-14 22:01 [PATCH 0/4] user namespace fixes Eric W. Biederman
2012-12-14 22:03 ` [PATCH 1/4] Fix cap_capable to only allow owners in the parent user namespace to have caps Eric W. Biederman
2012-12-14 22:03 ` [PATCH 2/4] userns: Require CAP_SYS_ADMIN for most uses of setns Eric W. Biederman
2012-12-14 23:35   ` Serge E. Hallyn
2012-12-17 19:03   ` Andy Lutomirski
2012-12-14 22:04 ` [PATCH 3/4] userns: Add a more complete capability subset test to commit_creds Eric W. Biederman
2012-12-15  0:03   ` Serge E. Hallyn
2012-12-15  0:11     ` Eric W. Biederman
2012-12-15  0:47       ` Serge E. Hallyn
2012-12-15  0:48         ` Eric W. Biederman
2012-12-15  2:06           ` Serge E. Hallyn [this message]
2012-12-17 19:08           ` Andy Lutomirski
2012-12-14 22:05 ` [PATCH 4/4] userns: Fix typo in description of the limitation of userns_install Eric W. Biederman
2012-12-14 23:36   ` Serge E. Hallyn
2012-12-17 19:08   ` Andy Lutomirski
2012-12-17 19:03 ` [PATCH 0/4] user namespace fixes Andy Lutomirski
2012-12-17 21:01   ` Eric W. Biederman

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