From: Seth Forshee <seth.forshee@canonical.com> To: "Eric W. Biederman" <ebiederm@xmission.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Serge Hallyn <serge.hallyn@canonical.com>, James Morris <james.l.morris@oracle.com>, "Serge E. Hallyn" <serge@hallyn.com>, Paul Moore <paul@paul-moore.com>, Stephen Smalley <sds@tycho.nsa.gov>, Eric Paris <eparis@parisplace.org> Cc: Miklos Szeredi <mszeredi@redhat.com>, Seth Forshee <seth.forshee@canonical.com>, dm-devel@redhat.com, linux-security-module@vger.kernel.org, Richard Weinberger <richard.weinberger@gmail.com>, linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, fuse-devel@lists.sourceforge.net, Austin S Hemmelgarn <ahferroin7@gmail.com>, linux-mtd@lists.infradead.org, selinux@tycho.nsa.gov, linux-fsdevel@vger.kernel.org, cgroups@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com> Subject: [PATCH v4 06/21] fs: Treat foreign mounts as nosuid Date: Tue, 26 Apr 2016 14:36:19 -0500 [thread overview] Message-ID: <1461699396-33000-7-git-send-email-seth.forshee@canonical.com> (raw) In-Reply-To: <1461699396-33000-1-git-send-email-seth.forshee@canonical.com> From: Andy Lutomirski <luto@amacapital.net> If a process gets access to a mount from a different user namespace, that process should not be able to take advantage of setuid files or selinux entrypoints from that filesystem. Prevent this by treating mounts from other mount namespaces and those not owned by current_user_ns() or an ancestor as nosuid. This will make it safer to allow more complex filesystems to be mounted in non-root user namespaces. This does not remove the need for MNT_LOCK_NOSUID. The setuid, setgid, and file capability bits can no longer be abused if code in a user namespace were to clear nosuid on an untrusted filesystem, but this patch, by itself, is insufficient to protect the system from abuse of files that, when execed, would increase MAC privilege. As a more concrete explanation, any task that can manipulate a vfsmount associated with a given user namespace already has capabilities in that namespace and all of its descendents. If they can cause a malicious setuid, setgid, or file-caps executable to appear in that mount, then that executable will only allow them to elevate privileges in exactly the set of namespaces in which they are already privileges. On the other hand, if they can cause a malicious executable to appear with a dangerous MAC label, running it could change the caller's security context in a way that should not have been possible, even inside the namespace in which the task is confined. As a hardening measure, this would have made CVE-2014-5207 much more difficult to exploit. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> --- fs/exec.c | 2 +- fs/namespace.c | 13 +++++++++++++ include/linux/mount.h | 1 + security/commoncap.c | 8 +++++++- security/selinux/hooks.c | 2 +- 5 files changed, 23 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index c4010b8207a1..706088dd0cb1 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1391,7 +1391,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm) bprm->cred->euid = current_euid(); bprm->cred->egid = current_egid(); - if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + if (!mnt_may_suid(bprm->file->f_path.mnt)) return; if (task_no_new_privs(current)) diff --git a/fs/namespace.c b/fs/namespace.c index c133318bec35..6e9db4c166b4 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3284,6 +3284,19 @@ found: return visible; } +bool mnt_may_suid(struct vfsmount *mnt) +{ + /* + * Foreign mounts (accessed via fchdir or through /proc + * symlinks) are always treated as if they are nosuid. This + * prevents namespaces from trusting potentially unsafe + * suid/sgid bits, file caps, or security labels that originate + * in other namespaces. + */ + return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) && + in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns); +} + static struct ns_common *mntns_get(struct task_struct *task) { struct ns_common *ns = NULL; diff --git a/include/linux/mount.h b/include/linux/mount.h index f822c3c11377..54a594d49733 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -81,6 +81,7 @@ extern void mntput(struct vfsmount *mnt); extern struct vfsmount *mntget(struct vfsmount *mnt); extern struct vfsmount *mnt_clone_internal(struct path *path); extern int __mnt_is_readonly(struct vfsmount *mnt); +extern bool mnt_may_suid(struct vfsmount *mnt); struct path; extern struct vfsmount *clone_private_mount(struct path *path); diff --git a/security/commoncap.c b/security/commoncap.c index 8912ef117faa..a306c5d90709 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -453,8 +453,14 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c if (!file_caps_enabled) return 0; - if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + if (!mnt_may_suid(bprm->file->f_path.mnt)) return 0; + + /* + * This check is redundant with mnt_may_suid() but is kept to make + * explicit that capability bits are limited to s_user_ns and its + * descendants. + */ if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns)) return 0; diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 912deee3f01e..1350167635cb 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2234,7 +2234,7 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm, const struct task_security_struct *new_tsec) { int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS); - int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID); + int nosuid = !mnt_may_suid(bprm->file->f_path.mnt); int rc; if (!nnp && !nosuid) -- 2.7.4 ______________________________________________________ Linux MTD discussion mailing list http://lists.infradead.org/mailman/listinfo/linux-mtd/
WARNING: multiple messages have this Message-ID (diff)
From: Seth Forshee <seth.forshee@canonical.com> To: "Eric W. Biederman" <ebiederm@xmission.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Serge Hallyn <serge.hallyn@canonical.com>, James Morris <james.l.morris@oracle.com>, "Serge E. Hallyn" <serge@hallyn.com>, Paul Moore <paul@paul-moore.com>, Stephen Smalley <sds@tycho.nsa.gov>, Eric Paris <eparis@parisplace.org> Cc: Richard Weinberger <richard.weinberger@gmail.com>, Austin S Hemmelgarn <ahferroin7@gmail.com>, Miklos Szeredi <mszeredi@redhat.com>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, linux-kernel@vger.kernel.org, linux-bcache@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, fuse-devel@lists.sourceforge.net, linux-security-module@vger.kernel.org, selinux@tycho.nsa.gov, cgroups@vger.kernel.org, Seth Forshee <seth.forshee@canonical.com>, Andy Lutomirski <luto@amacapital.net> Subject: [PATCH v4 06/21] fs: Treat foreign mounts as nosuid Date: Tue, 26 Apr 2016 14:36:19 -0500 [thread overview] Message-ID: <1461699396-33000-7-git-send-email-seth.forshee@canonical.com> (raw) In-Reply-To: <1461699396-33000-1-git-send-email-seth.forshee@canonical.com> From: Andy Lutomirski <luto@amacapital.net> If a process gets access to a mount from a different user namespace, that process should not be able to take advantage of setuid files or selinux entrypoints from that filesystem. Prevent this by treating mounts from other mount namespaces and those not owned by current_user_ns() or an ancestor as nosuid. This will make it safer to allow more complex filesystems to be mounted in non-root user namespaces. This does not remove the need for MNT_LOCK_NOSUID. The setuid, setgid, and file capability bits can no longer be abused if code in a user namespace were to clear nosuid on an untrusted filesystem, but this patch, by itself, is insufficient to protect the system from abuse of files that, when execed, would increase MAC privilege. As a more concrete explanation, any task that can manipulate a vfsmount associated with a given user namespace already has capabilities in that namespace and all of its descendents. If they can cause a malicious setuid, setgid, or file-caps executable to appear in that mount, then that executable will only allow them to elevate privileges in exactly the set of namespaces in which they are already privileges. On the other hand, if they can cause a malicious executable to appear with a dangerous MAC label, running it could change the caller's security context in a way that should not have been possible, even inside the namespace in which the task is confined. As a hardening measure, this would have made CVE-2014-5207 much more difficult to exploit. Signed-off-by: Andy Lutomirski <luto@amacapital.net> Signed-off-by: Seth Forshee <seth.forshee@canonical.com> Acked-by: James Morris <james.l.morris@oracle.com> Acked-by: Serge Hallyn <serge.hallyn@canonical.com> --- fs/exec.c | 2 +- fs/namespace.c | 13 +++++++++++++ include/linux/mount.h | 1 + security/commoncap.c | 8 +++++++- security/selinux/hooks.c | 2 +- 5 files changed, 23 insertions(+), 3 deletions(-) diff --git a/fs/exec.c b/fs/exec.c index c4010b8207a1..706088dd0cb1 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1391,7 +1391,7 @@ static void bprm_fill_uid(struct linux_binprm *bprm) bprm->cred->euid = current_euid(); bprm->cred->egid = current_egid(); - if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + if (!mnt_may_suid(bprm->file->f_path.mnt)) return; if (task_no_new_privs(current)) diff --git a/fs/namespace.c b/fs/namespace.c index c133318bec35..6e9db4c166b4 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3284,6 +3284,19 @@ found: return visible; } +bool mnt_may_suid(struct vfsmount *mnt) +{ + /* + * Foreign mounts (accessed via fchdir or through /proc + * symlinks) are always treated as if they are nosuid. This + * prevents namespaces from trusting potentially unsafe + * suid/sgid bits, file caps, or security labels that originate + * in other namespaces. + */ + return !(mnt->mnt_flags & MNT_NOSUID) && check_mnt(real_mount(mnt)) && + in_userns(current_user_ns(), mnt->mnt_sb->s_user_ns); +} + static struct ns_common *mntns_get(struct task_struct *task) { struct ns_common *ns = NULL; diff --git a/include/linux/mount.h b/include/linux/mount.h index f822c3c11377..54a594d49733 100644 --- a/include/linux/mount.h +++ b/include/linux/mount.h @@ -81,6 +81,7 @@ extern void mntput(struct vfsmount *mnt); extern struct vfsmount *mntget(struct vfsmount *mnt); extern struct vfsmount *mnt_clone_internal(struct path *path); extern int __mnt_is_readonly(struct vfsmount *mnt); +extern bool mnt_may_suid(struct vfsmount *mnt); struct path; extern struct vfsmount *clone_private_mount(struct path *path); diff --git a/security/commoncap.c b/security/commoncap.c index 8912ef117faa..a306c5d90709 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -453,8 +453,14 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c if (!file_caps_enabled) return 0; - if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) + if (!mnt_may_suid(bprm->file->f_path.mnt)) return 0; + + /* + * This check is redundant with mnt_may_suid() but is kept to make + * explicit that capability bits are limited to s_user_ns and its + * descendants. + */ if (!in_userns(current_user_ns(), bprm->file->f_path.mnt->mnt_sb->s_user_ns)) return 0; diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index 912deee3f01e..1350167635cb 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -2234,7 +2234,7 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm, const struct task_security_struct *new_tsec) { int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS); - int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID); + int nosuid = !mnt_may_suid(bprm->file->f_path.mnt); int rc; if (!nnp && !nosuid) -- 2.7.4
next prev parent reply other threads:[~2016-04-26 19:36 UTC|newest] Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-04-26 19:36 [PATCH v4 00/21] Support fuse mounts in user namespaces Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 01/21] fs: fix a posible leak of allocated superblock Seth Forshee 2016-04-26 19:36 ` [PATCH v4 04/21] block_dev: Support checking inode permissions in lookup_bdev() Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 05/21] block_dev: Check permissions towards block device inode when mounting Seth Forshee 2016-04-26 19:36 ` Seth Forshee [this message] 2016-04-26 19:36 ` [PATCH v4 06/21] fs: Treat foreign mounts as nosuid Seth Forshee 2016-04-26 19:36 ` [PATCH v4 08/21] userns: Replace in_userns with current_in_userns Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 09/21] Smack: Handle labels consistently in untrusted mounts Seth Forshee 2016-04-26 19:36 ` [PATCH v4 10/21] fs: Check for invalid i_uid in may_follow_link() Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-05-24 15:55 ` Djalal Harouni 2016-04-26 19:36 ` [PATCH v4 11/21] cred: Reject inodes with invalid ids in set_create_file_as() Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 15/21] fs: Don't remove suid for CAP_FSETID in s_user_ns Seth Forshee 2016-04-26 19:36 ` Seth Forshee [not found] ` <1461699396-33000-1-git-send-email-seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org> 2016-04-26 19:36 ` [PATCH v4 02/21] fs: Remove check of s_user_ns for existing mounts in fs_fully_visible() Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 03/21] fs: Allow sysfs and cgroupfs to share super blocks between user namespaces Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 07/21] selinux: Add support for unprivileged mounts from " Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 12/21] fs: Refuse uid/gid changes which don't map into s_user_ns Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 13/21] fs: Update posix_acl support to handle user namespace mounts Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 14/21] fs: Allow superblock owner to change ownership of inodes with unmappable ids Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 16/21] fs: Allow superblock owner to access do_remount_sb() Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 17/21] capabilities: Allow privileged user in s_user_ns to set security.* xattrs Seth Forshee 2016-04-26 19:36 ` Seth Forshee [not found] ` <1461699396-33000-18-git-send-email-seth.forshee-Z7WLFzj8eWMS+FvcfC7Uqw@public.gmane.org> 2016-04-27 7:22 ` James Morris 2016-04-27 7:22 ` James Morris 2016-04-26 19:36 ` [PATCH v4 18/21] fuse: Add support for pid namespaces Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-07-20 2:44 ` Sheng Yang [not found] ` <CA+2rt426_pshAauQizcxkfAq16vmEpB4sJ4genW_ucosH3j=zQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org> 2016-07-20 12:52 ` Seth Forshee 2016-07-20 12:52 ` Seth Forshee 2016-07-20 22:28 ` Sheng Yang 2016-07-21 7:25 ` Miklos Szeredi 2016-07-21 7:25 ` Miklos Szeredi 2016-04-26 19:36 ` [PATCH v4 19/21] fuse: Support fuse filesystems outside of init_user_ns Seth Forshee 2016-04-26 19:36 ` Seth Forshee 2016-04-26 19:36 ` [PATCH v4 20/21] fuse: Restrict allow_other to the superblock's namespace or a descendant Seth Forshee 2016-04-26 19:36 ` [PATCH v4 21/21] fuse: Allow user namespace mounts Seth Forshee
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=1461699396-33000-7-git-send-email-seth.forshee@canonical.com \ --to=seth.forshee@canonical.com \ --cc=ahferroin7@gmail.com \ --cc=cgroups@vger.kernel.org \ --cc=dm-devel@redhat.com \ --cc=ebiederm@xmission.com \ --cc=eparis@parisplace.org \ --cc=fuse-devel@lists.sourceforge.net \ --cc=james.l.morris@oracle.com \ --cc=linux-bcache@vger.kernel.org \ --cc=linux-fsdevel@vger.kernel.org \ --cc=linux-kernel@vger.kernel.org \ --cc=linux-mtd@lists.infradead.org \ --cc=linux-raid@vger.kernel.org \ --cc=linux-security-module@vger.kernel.org \ --cc=luto@amacapital.net \ --cc=mszeredi@redhat.com \ --cc=paul@paul-moore.com \ --cc=ptikhomirov@virtuozzo.com \ --cc=richard.weinberger@gmail.com \ --cc=sds@tycho.nsa.gov \ --cc=selinux@tycho.nsa.gov \ --cc=serge.hallyn@canonical.com \ --cc=serge@hallyn.com \ --cc=viro@zeniv.linux.org.uk \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: linkBe sure your reply has a Subject: header at the top and a blank line before the message body.
This is an external index of several public inboxes, see mirroring instructions on how to clone and mirror all data and code used by this external index.