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Upstream-Status: Pending
diff --git a/docs/capng_lock.3 b/docs/capng_lock.3
index 7683119..a070c1e 100644
--- a/docs/capng_lock.3
+++ b/docs/capng_lock.3
@@ -8,12 +8,13 @@ int capng_lock(void);
.SH "DESCRIPTION"
-capng_lock will take steps to prevent children of the current process to regain full privileges if the uid is 0. This should be called while possessing the CAP_SETPCAP capability in the kernel. This function will do the following if permitted by the kernel: Set the NOROOT option on for PR_SET_SECUREBITS, set the NOROOT_LOCKED option to on for PR_SET_SECUREBITS, set the PR_NO_SETUID_FIXUP option on for PR_SET_SECUREBITS, and set the PR_NO_SETUID_FIXUP_LOCKED option on for PR_SET_SECUREBITS.
+capng_lock will take steps to prevent children of the current process from gaining privileges by executing setuid programs. This should be called while possessing the CAP_SETPCAP capability in the kernel.
+This function will do the following if permitted by the kernel: If the kernel supports PR_SET_NO_NEW_PRIVS, it will use it. Otherwise it will set the NOROOT option on for PR_SET_SECUREBITS, set the NOROOT_LOCKED option to on for PR_SET_SECUREBITS, set the PR_NO_SETUID_FIXUP option on for PR_SET_SECUREBITS, and set the PR_NO_SETUID_FIXUP_LOCKED option on for PR_SET_SECUREBITS. If both fail, it will return an error.
.SH "RETURN VALUE"
-This returns 0 on success and a negative number on failure. -1 means a failure setting any of the PR_SET_SECUREBITS options.
+This returns 0 on success and a negative number on failure. -1 means a failure to use PR_SET_NO_NEW_PRIVS and a failure setting any of the PR_SET_SECUREBITS options.
.SH "SEE ALSO"
diff --git a/src/cap-ng.c b/src/cap-ng.c
index bd105ba..422f2bc 100644
--- a/src/cap-ng.c
+++ b/src/cap-ng.c
@@ -45,6 +45,7 @@
* 2.6.24 kernel XATTR_NAME_CAPS
* 2.6.25 kernel PR_CAPBSET_DROP, CAPABILITY_VERSION_2
* 2.6.26 kernel PR_SET_SECUREBITS, SECURE_*_LOCKED, VERSION_3
+ * 3.5 kernel PR_SET_NO_NEW_PRIVS
*/
/* External syscall prototypes */
@@ -122,6 +123,14 @@ extern int capget(cap_user_header_t header, const cap_user_data_t data);
#define SECURE_NO_SETUID_FIXUP_LOCKED 3 /* make bit-2 immutable */
#endif
+/* prctl values that we use */
+#ifndef PR_SET_SECUREBITS
+#define PR_SET_SECUREBITS 28
+#endif
+#ifndef PR_SET_NO_NEW_PRIVS
+#define PR_SET_NO_NEW_PRIVS 38
+#endif
+
// States: new, allocated, initted, updated, applied
typedef enum { CAPNG_NEW, CAPNG_ERROR, CAPNG_ALLOCATED, CAPNG_INIT,
CAPNG_UPDATED, CAPNG_APPLIED } capng_states_t;
@@ -663,15 +672,22 @@ int capng_change_id(int uid, int gid, capng_flags_t flag)
int capng_lock(void)
{
-#ifdef PR_SET_SECUREBITS
- int rc = prctl(PR_SET_SECUREBITS,
- 1 << SECURE_NOROOT |
- 1 << SECURE_NOROOT_LOCKED |
- 1 << SECURE_NO_SETUID_FIXUP |
- 1 << SECURE_NO_SETUID_FIXUP_LOCKED, 0, 0, 0);
+ int rc;
+
+ // On Linux 3.5 and up, we can directly prevent ourselves and
+ // our descendents from gaining privileges.
+ if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) == 0)
+ return 0;
+
+ // This kernel is too old or otherwise doesn't support
+ // PR_SET_NO_NEW_PRIVS. Fall back to using securebits.
+ rc = prctl(PR_SET_SECUREBITS,
+ 1 << SECURE_NOROOT |
+ 1 << SECURE_NOROOT_LOCKED |
+ 1 << SECURE_NO_SETUID_FIXUP |
+ 1 << SECURE_NO_SETUID_FIXUP_LOCKED, 0, 0, 0);
if (rc)
return -1;
-#endif
return 0;
}
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