audit: call audit_bprm() only once to add AUDIT_EXECVE information

Move the audit_bprm() call from search_binary_handler() to exec_binprm().  This
allows us to get rid of the mm member of struct audit_aux_data_execve since
bprm->mm will equal current->mm.

This also mitigates the issue that ->argc could be modified by the
load_binary() call in search_binary_handler().

audit_bprm() was being called to add an AUDIT_EXECVE record to the audit
context every time search_binary_handler() was recursively called.  Only one
reference is necessary.
Reported-by: Oleg Nesterov <onestero@redhat.com>
Cc: Eric Paris <eparis@redhat.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
---
This patch is against 3.11, but was developed on Oleg's post-3.11 patches that
introduce exec_binprm().

fs/exec.c

@@ -1383,10 +1383,6 @@ int search_binary_handler(struct linux_binprm *bprm)
 	if (retval)
 		return retval;
 
-	retval = audit_bprm(bprm);
-	if (retval)
-		return retval;
-
 	/* Need to fetch pid before load_binary changes it */
 	old_pid = current->pid;
 	rcu_read_lock();
@@ -1408,6 +1404,7 @@ int search_binary_handler(struct linux_binprm *bprm)
 			bprm->recursion_depth = depth;
 			if (retval >= 0) {
 				if (depth == 0) {
+					audit_bprm(bprm);
 					trace_sched_process_exec(current, old_pid, bprm);
 					ptrace_event(PTRACE_EVENT_EXEC, old_vpid);
 				}

include/linux/audit.h

@@ -238,11 +238,10 @@ static inline void audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid
 	if (unlikely(!audit_dummy_context()))
 		__audit_ipc_set_perm(qbytes, uid, gid, mode);
 }
-static inline int audit_bprm(struct linux_binprm *bprm)
+static inline void audit_bprm(struct linux_binprm *bprm)
 {
 	if (unlikely(!audit_dummy_context()))
 		__audit_bprm(bprm);
-	return 0;
 }
 static inline int audit_socketcall(int nargs, unsigned long *args)
 {
@@ -369,10 +368,8 @@ static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
 static inline void audit_ipc_set_perm(unsigned long qbytes, uid_t uid,
 					gid_t gid, umode_t mode)
 { }
-static inline int audit_bprm(struct linux_binprm *bprm)
-{
-	return 0;
-}
+static inline void audit_bprm(struct linux_binprm *bprm)
+{ }
 static inline int audit_socketcall(int nargs, unsigned long *args)
 {
 	return 0;

kernel/audit.h

@@ -199,7 +199,6 @@ struct audit_context {
 		} mmap;
 		struct {
 			int			argc;
-			struct mm_struct	*mm;
 		} execve;
 	};
 	int fds[2];

kernel/auditsc.c

@@ -1145,9 +1145,6 @@ static void audit_log_execve_info(struct audit_context *context,
 	const char __user *p;
 	char *buf;
 
-	if (context->execve.mm != current->mm)
-		return; /* execve failed, no additional info */
-
 	p = (const char __user *)current->mm->arg_start;
 
 	audit_log_format(*ab, "argc=%d", context->execve.argc);
@@ -2144,7 +2141,6 @@ void __audit_bprm(struct linux_binprm *bprm)
 
 	context->type = AUDIT_EXECVE;
 	context->execve.argc = bprm->argc;
-	context->execve.mm = bprm->mm;
 }