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[199.87.125.144]) by smtp.gmail.com with ESMTPSA id u4sm2626101igz.8.2015.09.16.13.03.48 (version=TLSv1.2 cipher=RC4-SHA bits=128/128); Wed, 16 Sep 2015 13:03:48 -0700 (PDT) From: Seth Forshee To: "Eric W. Biederman" , Alexander Viro , Serge Hallyn , James Morris , "Serge E. Hallyn" Cc: 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, Seth Forshee Subject: [PATCH v3 4/7] fs: Limit file caps to the user namespace of the super block Date: Wed, 16 Sep 2015 15:02:40 -0500 Message-Id: <1442433764-80826-5-git-send-email-seth.forshee@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1442433764-80826-1-git-send-email-seth.forshee@canonical.com> References: <1442433764-80826-1-git-send-email-seth.forshee@canonical.com> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Spam-Status: No, score=-6.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, T_RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP 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. 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) {