[PATCH V3 10/10] capabilities: audit log other surprising conditions

[Richard Guy Briggs]

The existing condition tested for process effective capabilities set by file
attributes but intended to ignore the change if the result was unsurprisingly an
effective full set in the case root is special with a setuid root executable
file and we are root.

Stated again:
- When you execute a setuid root application, it is no surprise and expected
that it got all capabilities, so we do not want capabilities recorded.
        if (pE_grew && !(pE_fullset && (eff_root || real_root) && root_priveleged) )

Now make sure we cover other cases:
- If something prevented a setuid root app getting all capabilities and it
wound up with one capability only, then it is a surprise and should be logged.
When it is a setuid root file, we only want capabilities when the process does
not get full capabilities..
        root_priveleged && setuid_root && !pE_fullset

- Similarly if a non-setuid program does pick up capabilities due to file system
based capabilities, then we want to know what capabilities were picked up.
When it has file system based capabilities we want the capabilities.
        !is_setuid && (has_fcap && pP_gained)

- If it is a non-setuid file and it gets ambient capabilities, we want the
capabilities.
        !is_setuid && pA_gained

- These last two are combined into one due to the common first parameter.

Related: https://github.com/linux-audit/audit-kernel/issues/16

Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
---
 security/commoncap.c |   28 ++++++++++++++++++++--------
 1 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/security/commoncap.c b/security/commoncap.c
index 49cce06..8da965c 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -536,7 +536,7 @@ static inline bool is_setgid(struct cred *new, const struct cred *old)
 { return !gid_eq(new->egid, old->gid); }
 
 /*
- * Audit candidate if current->cap_effective is set
+ * 1) Audit candidate if current->cap_effective is set
  *
  * We do not bother to audit if 3 things are true:
  *   1) cap_effective has all caps
@@ -546,16 +546,28 @@ static inline bool is_setgid(struct cred *new, const struct cred *old)
  *
  * Number 1 above might fail if you don't have a full bset, but I think
  * that is interesting information to audit.
+ *
+ * A number of other conditions require logging:
+ * 2) something prevented setuid root getting all caps
+ * 3) non-setuid root gets fcaps
+ * 4) non-setuid root gets ambient
  */
-static inline bool nonroot_raised_pE(struct cred *cred, kuid_t root)
+static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old, kuid_t root, bool has_fcap)
 {
 	bool ret = false;
 
-	if (cap_grew(effective, ambient, cred) &&
-	    !(cap_full(effective, cred) &&
-	      (is_eff(root, cred) ||
-	       is_real(root, cred)) &&
-	      root_privileged()))
+	if ((cap_grew(effective, ambient, new) &&
+	     !(cap_full(effective, new) &&
+	       (is_eff(root, new) ||
+	        is_real(root, new)) &&
+	       root_privileged())) ||
+	    (root_privileged() &&
+	     is_suid(root, new) &&
+	     !cap_full(effective, new)) ||
+	    (!is_setuid(new, old) &&
+	     ((has_fcap &&
+               cap_gained(permitted, new, old)) ||
+              cap_gained(ambient, new, old))))
 		ret = true;
 	return ret;
 }
@@ -639,7 +651,7 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
 
 	bprm->cap_effective = effective;
 
-	if (nonroot_raised_pE(new, root_uid)) {
+	if (nonroot_raised_pE(new, old, root_uid, has_fcap)) {
 		ret = audit_log_bprm_fcaps(bprm, new, old);
 		if (ret < 0)
 			return ret;
-- 
1.7.1