From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out02.mta.xmission.com ([166.70.13.232]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1ZfEfd-0007uk-5T for linux-mtd@lists.infradead.org; Thu, 24 Sep 2015 22:07:17 +0000 From: ebiederm@xmission.com (Eric W. Biederman) To: Seth Forshee Cc: Alexander Viro , Serge Hallyn , James Morris , "Serge E. Hallyn" , Andy Lutomirski , linux-fsdevel@vger.kernel.org, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, linux-kernel@vger.kernel.org, linux-mtd@lists.infradead.org References: <1443039368-55445-1-git-send-email-seth.forshee@canonical.com> <1443039368-55445-5-git-send-email-seth.forshee@canonical.com> Date: Thu, 24 Sep 2015 16:59:35 -0500 In-Reply-To: <1443039368-55445-5-git-send-email-seth.forshee@canonical.com> (Seth Forshee's message of "Wed, 23 Sep 2015 15:16:04 -0500") Message-ID: <87fv23o4vs.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [PATCH v4 4/7] fs: Limit file caps to the user namespace of the super block List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Seth Forshee writes: > Capability sets attached to files must be ignored except in the > user namespaces where the mounter is privileged, i.e. s_user_ns > and its descendants. Otherwise a vector exists for gaining > privileges in namespaces where a user is not already privileged. > > Add a new helper function, in_user_ns(), to test whether a user > namespace is the same as or a descendant of another namespace. > Use this helper to determine whether a file's capability set > should be applied to the caps constructed during exec. No issues with this but given that we always pass current_user_ns() we may want to simplify the users of in_user_ns by renaming it current_in_user_ns() and hard codeing current_user_ns(). Eric > Acked-by: Serge Hallyn > Signed-off-by: Seth Forshee > --- > include/linux/user_namespace.h | 8 ++++++++ > kernel/user_namespace.c | 14 ++++++++++++++ > security/commoncap.c | 2 ++ > 3 files changed, 24 insertions(+) > > diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h > index 8297e5b341d8..a43faa727124 100644 > --- a/include/linux/user_namespace.h > +++ b/include/linux/user_namespace.h > @@ -72,6 +72,8 @@ extern ssize_t proc_projid_map_write(struct file *, const char __user *, size_t, > extern ssize_t proc_setgroups_write(struct file *, const char __user *, size_t, loff_t *); > extern int proc_setgroups_show(struct seq_file *m, void *v); > extern bool userns_may_setgroups(const struct user_namespace *ns); > +extern bool in_userns(const struct user_namespace *ns, > + const struct user_namespace *target_ns); > #else > > static inline struct user_namespace *get_user_ns(struct user_namespace *ns) > @@ -100,6 +102,12 @@ static inline bool userns_may_setgroups(const struct user_namespace *ns) > { > return true; > } > + > +static inline bool in_userns(const struct user_namespace *ns, > + const struct user_namespace *target_ns) > +{ > + return true; > +} > #endif > > #endif /* _LINUX_USER_H */ > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c > index 88fefa68c516..69fbc377357b 100644 > --- a/kernel/user_namespace.c > +++ b/kernel/user_namespace.c > @@ -945,6 +945,20 @@ bool userns_may_setgroups(const struct user_namespace *ns) > return allowed; > } > > +/* > + * Returns true if @ns is the same namespace as or a descendant of > + * @target_ns. > + */ > +bool in_userns(const struct user_namespace *ns, > + const struct user_namespace *target_ns) > +{ > + for (; ns; ns = ns->parent) { > + if (ns == target_ns) > + return true; > + } > + return false; > +} > + > static inline struct user_namespace *to_user_ns(struct ns_common *ns) > { > return container_of(ns, struct user_namespace, ns); > diff --git a/security/commoncap.c b/security/commoncap.c > index 1832cf701c3d..400aa224b491 100644 > --- a/security/commoncap.c > +++ b/security/commoncap.c > @@ -450,6 +450,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c > > if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) > return 0; > + if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns)) > + return 0; > > rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps); > if (rc < 0) {