Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753104AbbLZVRd (ORCPT ); Sat, 26 Dec 2015 16:17:33 -0500 Received: from h2.hallyn.com ([78.46.35.8]:37558 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752108AbbLZVRb (ORCPT ); Sat, 26 Dec 2015 16:17:31 -0500 Date: Sat, 26 Dec 2015 15:17:29 -0600 From: "Serge E. Hallyn" To: Jann Horn Cc: Roland McGrath , Oleg Nesterov , linux-kernel@vger.kernel.org, security@kernel.org, Serge Hallyn , Andy Lutomirski , "Eric W. Biederman" Subject: Re: [PATCH] ptrace: being capable wrt a process requires mapped uids/gids Message-ID: <20151226211729.GC19815@mail.hallyn.com> References: <20151226011038.GA25455@pc.thejh.net> <1451098351-8917-1-git-send-email-jann@thejh.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1451098351-8917-1-git-send-email-jann@thejh.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4636 Lines: 118 On Sat, Dec 26, 2015 at 03:52:31AM +0100, Jann Horn wrote: > ptrace_has_cap() checks whether the current process should be > treated as having a certain capability for ptrace checks > against another process. Until now, this was equivalent to > has_ns_capability(current, target_ns, CAP_SYS_PTRACE). > > However, if a root-owned process wants to enter a user > namespace for some reason without knowing who owns it and > therefore can't change to the namespace owner's uid and gid > before entering, as soon as it has entered the namespace, > the namespace owner can attach to it via ptrace and thereby > gain access to its uid and gid. > > While it is possible for the entering process to switch to > the uid of a claimed namespace owner before entering, > causing the attempt to enter to fail if the claimed uid is > wrong, this doesn't solve the problem of determining an > appropriate gid. > > With this change, the entering process can first enter the > namespace and then safely inspect the namespace's > properties, e.g. through /proc/self/{uid_map,gid_map}, > assuming that the namespace owner doesn't have access to > uid 0. > > Changed in v2: The caller needs to be capable in the > namespace into which tcred's uids/gids can be mapped. > > Signed-off-by: Jann Horn > --- > kernel/ptrace.c | 33 ++++++++++++++++++++++++++++----- > 1 file changed, 28 insertions(+), 5 deletions(-) > > diff --git a/kernel/ptrace.c b/kernel/ptrace.c > index b760bae..260a08d 100644 > --- a/kernel/ptrace.c > +++ b/kernel/ptrace.c > @@ -20,6 +20,7 @@ > #include > #include > #include > +#include > #include > #include > #include > @@ -207,12 +208,34 @@ static int ptrace_check_attach(struct task_struct *child, bool ignore_state) > return ret; > } > > -static int ptrace_has_cap(struct user_namespace *ns, unsigned int mode) > +static bool ptrace_has_cap(const struct cred *tcred, unsigned int mode) > { > + struct user_namespace *tns = tcred->user_ns; > + > + /* When a root-owned process enters a user namespace created by a > + * malicious user, the user shouldn't be able to execute code under > + * uid 0 by attaching to the root-owned process via ptrace. > + * Therefore, similar to the capable_wrt_inode_uidgid() check, > + * verify that all the uids and gids of the target process are > + * mapped into a namespace below the current one in which the caller > + * is capable. > + * No fsuid/fsgid check because __ptrace_may_access doesn't do it > + * either. > + */ > + while ( > + !kuid_has_mapping(tns, tcred->euid) || > + !kuid_has_mapping(tns, tcred->suid) || > + !kuid_has_mapping(tns, tcred->uid) || > + !kgid_has_mapping(tns, tcred->egid) || > + !kgid_has_mapping(tns, tcred->sgid) || > + !kgid_has_mapping(tns, tcred->gid)) { > + tns = tns->parent; Sorry, i can't quite remember - is there a way for a task in init_user_ns to have INVALID_UID | INVALID_GID ? I.e. any point in breaking here if tns == &init_user_n? > + } > + > if (mode & PTRACE_MODE_NOAUDIT) > - return has_ns_capability_noaudit(current, ns, CAP_SYS_PTRACE); > + return has_ns_capability_noaudit(current, tns, CAP_SYS_PTRACE); > else > - return has_ns_capability(current, ns, CAP_SYS_PTRACE); > + return has_ns_capability(current, tns, CAP_SYS_PTRACE); > } > > /* Returns 0 on success, -errno on denial. */ > @@ -241,7 +264,7 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode) > gid_eq(cred->gid, tcred->sgid) && > gid_eq(cred->gid, tcred->gid)) > goto ok; > - if (ptrace_has_cap(tcred->user_ns, mode)) > + if (ptrace_has_cap(tcred, mode)) > goto ok; > rcu_read_unlock(); > return -EPERM; > @@ -252,7 +275,7 @@ ok: > dumpable = get_dumpable(task->mm); > rcu_read_lock(); > if (dumpable != SUID_DUMP_USER && > - !ptrace_has_cap(__task_cred(task)->user_ns, mode)) { > + !ptrace_has_cap(__task_cred(task), mode)) { > rcu_read_unlock(); > return -EPERM; > } > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/