path: root/security/commoncap.c
diff options
authorSerge E. Hallyn <serue@us.ibm.com>2009-04-02 18:47:14 -0500
committerJames Morris <jmorris@namei.org>2009-04-03 11:49:31 +1100
commitb5f22a59c0356655a501190959db9f7f5dd07e3f (patch)
tree3c20437a6a3b7b7e980078bfbcd0d53cdeda7528 /security/commoncap.c
parentmodules: sysctl to block module loading (diff)
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 <serue@us.ibm.com> Acked-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'security/commoncap.c')
1 files changed, 32 insertions, 0 deletions
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 <linux/prctl.h>
#include <linux/securebits.h>
+ * 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();
@@ -464,6 +486,15 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
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
* capability sets for the file.
@@ -478,6 +509,7 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
if (new->euid == 0)
effective = true;
/* Don't let someone trace a set[ug]id/setpcap binary with the revised
* credentials unless they have the appropriate permit