From b5f22a59c0356655a501190959db9f7f5dd07e3f Mon Sep 17 00:00:00 2001 From: "Serge E. Hallyn" Date: Thu, 2 Apr 2009 18:47:14 -0500 Subject: [PATCH] don't raise all privs on setuid-root file with fE set (v2) Distributions face a backward compatibility problem with starting to use file capabilities. For instance, removing setuid root from ping and doing setcap cap_net_raw=pe means that booting with an older kernel or one compiled without file capabilities means ping won't work for non-root users. In order to replace the setuid root bit on a capability-unaware program, one has to set the effective, or legacy, file capability, which makes the capability effective immediately. This patch uses the legacy bit as a queue to not automatically add full privilege to a setuid-root program. So, with this patch, an ordinary setuid-root program will run with privilege. But if /bin/ping has both setuid-root and cap_net_raw in fP and fE, then ping (when run by non-root user) will not run with only cap_net_raw. Changelog: Apr 2 2009: Print a message once when such a binary is loaded, as per James Morris' suggestion. Apr 2 2009: Fix the condition to only catch uid!=0 && euid==0. Signed-off-by: Serge E. Hallyn Acked-by: Casey Schaufler Signed-off-by: James Morris --- security/commoncap.c | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/security/commoncap.c b/security/commoncap.c index 7cd61a5f5205..97ac1f167717 100644 --- a/security/commoncap.c +++ b/security/commoncap.c @@ -28,6 +28,28 @@ #include #include +/* + * If a non-root user executes a setuid-root binary in + * !secure(SECURE_NOROOT) mode, then we raise capabilities. + * However if fE is also set, then the intent is for only + * the file capabilities to be applied, and the setuid-root + * bit is left on either to change the uid (plausible) or + * to get full privilege on a kernel without file capabilities + * support. So in that case we do not raise capabilities. + * + * Warn if that happens, once per boot. + */ +static void warn_setuid_and_fcaps_mixed(char *fname) +{ + static int warned; + if (!warned) { + printk(KERN_INFO "warning: `%s' has both setuid-root and" + " effective capabilities. Therefore not raising all" + " capabilities.\n", fname); + warned = 1; + } +} + int cap_netlink_send(struct sock *sk, struct sk_buff *skb) { NETLINK_CB(skb).eff_cap = current_cap(); @@ -463,6 +485,15 @@ int cap_bprm_set_creds(struct linux_binprm *bprm) return ret; if (!issecure(SECURE_NOROOT)) { + /* + * If the legacy file capability is set, then don't set privs + * for a setuid root binary run by a non-root user. Do set it + * for a root user just to cause least surprise to an admin. + */ + if (effective && new->uid != 0 && new->euid == 0) { + warn_setuid_and_fcaps_mixed(bprm->filename); + goto skip; + } /* * To support inheritance of root-permissions and suid-root * executables under compatibility mode, we override the @@ -478,6 +509,7 @@ int cap_bprm_set_creds(struct linux_binprm *bprm) if (new->euid == 0) effective = true; } +skip: /* Don't let someone trace a set[ug]id/setpcap binary with the revised * credentials unless they have the appropriate permit