path: root/security/commoncap.c
diff options
authorAndy Lutomirski <luto@amacapital.net>2016-06-23 16:41:05 -0500
committerEric W. Biederman <ebiederm@xmission.com>2016-06-24 10:40:41 -0500
commit380cf5ba6b0a0b307f4afb62b186ca801defb203 (patch)
treee5c5c1d0f2f87cc6eafb17d1d35c14c664e47d98 /security/commoncap.c
parentd07b846f6200454c50d791796edb82660192513d (diff)
fs: Treat foreign mounts as nosuid
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> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Diffstat (limited to 'security/commoncap.c')
1 files changed, 7 insertions, 1 deletions
diff --git a/security/commoncap.c b/security/commoncap.c
index e109e6dac858..14540bd78561 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 (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
return 0;

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