[PATCH] get rid of loginuid races

Keeping loginuid in audit_context is racy and results in messier
code.  Taken to task_struct, out of the way of ->audit_context
changes.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/audit.h

@@ -409,7 +409,7 @@ extern unsigned int audit_serial(void);
 extern void auditsc_get_stamp(struct audit_context *ctx,
 			      struct timespec *t, unsigned int *serial);
 extern int  audit_set_loginuid(struct task_struct *task, uid_t loginuid);
-extern uid_t audit_get_loginuid(struct task_struct *task);
+#define audit_get_loginuid(t) ((t)->loginuid)
 extern void audit_log_task_context(struct audit_buffer *ab);
 extern int __audit_ipc_obj(struct kern_ipc_perm *ipcp);
 extern int __audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, mode_t mode);

include/linux/init_task.h

@@ -114,6 +114,12 @@ extern struct group_info init_groups;
 	.pid = &init_struct_pid,				\
 }
 
+#ifdef CONFIG_AUDITSYSCALL
+#define INIT_IDS \
+	.loginuid = -1,
+#else
+#define INIT_IDS
+#endif
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -173,6 +179,7 @@ extern struct group_info init_groups;
 		[PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),		\
 	},								\
 	.dirties = INIT_PROP_LOCAL_SINGLE(dirties),			\
+	INIT_IDS							\
 	INIT_TRACE_IRQFLAGS						\
 	INIT_LOCKDEP							\
 }

include/linux/sched.h

@@ -1139,6 +1139,9 @@ struct task_struct {
 	void *security;
 #endif
 	struct audit_context *audit_context;
+#ifdef CONFIG_AUDITSYSCALL
+	uid_t loginuid;
+#endif
 	seccomp_t seccomp;
 
 /* Thread group tracking */

kernel/auditsc.c

@@ -192,7 +192,6 @@ struct audit_context {
 	enum audit_state    state;
 	unsigned int	    serial;     /* serial number for record */
 	struct timespec	    ctime;      /* time of syscall entry */
-	uid_t		    loginuid;   /* login uid (identity) */
 	int		    major;      /* syscall number */
 	unsigned long	    argv[4];    /* syscall arguments */
 	int		    return_valid; /* return code is valid */
@@ -506,7 +505,7 @@ static int audit_filter_rules(struct task_struct *tsk,
 		case AUDIT_LOGINUID:
 			result = 0;
 			if (ctx)
-				result = audit_comparator(ctx->loginuid, f->op, f->val);
+				result = audit_comparator(tsk->loginuid, f->op, f->val);
 			break;
 		case AUDIT_SUBJ_USER:
 		case AUDIT_SUBJ_ROLE:
@@ -783,11 +782,8 @@ static inline void audit_free_aux(struct audit_context *context)
 static inline void audit_zero_context(struct audit_context *context,
 				      enum audit_state state)
 {
-	uid_t loginuid = context->loginuid;
-
 	memset(context, 0, sizeof(*context));
 	context->state      = state;
-	context->loginuid   = loginuid;
 }
 
 static inline struct audit_context *audit_alloc_context(enum audit_state state)
@@ -826,11 +822,6 @@ int audit_alloc(struct task_struct *tsk)
 		return -ENOMEM;
 	}
 
-				/* Preserve login uid */
-	context->loginuid = -1;
-	if (current->audit_context)
-		context->loginuid = current->audit_context->loginuid;
-
 	tsk->audit_context  = context;
 	set_tsk_thread_flag(tsk, TIF_SYSCALL_AUDIT);
 	return 0;
@@ -1047,7 +1038,7 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
 		  context->name_count,
 		  context->ppid,
 		  context->pid,
-		  context->loginuid,
+		  tsk->loginuid,
 		  context->uid,
 		  context->gid,
 		  context->euid, context->suid, context->fsuid,
@@ -1779,39 +1770,22 @@ int audit_set_loginuid(struct task_struct *task, uid_t loginuid)
 {
 	struct audit_context *context = task->audit_context;
 
-	if (context) {
+	if (context && context->in_syscall) {
-		/* Only log if audit is enabled */
+		struct audit_buffer *ab;
-		if (context->in_syscall) {
-			struct audit_buffer *ab;
 
-			ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_LOGIN);
+		ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_LOGIN);
-			if (ab) {
+		if (ab) {
-				audit_log_format(ab, "login pid=%d uid=%u "
+			audit_log_format(ab, "login pid=%d uid=%u "
-					"old auid=%u new auid=%u",
+				"old auid=%u new auid=%u",
-					task->pid, task->uid,
+				task->pid, task->uid,
-					context->loginuid, loginuid);
+				task->loginuid, loginuid);
-				audit_log_end(ab);
+			audit_log_end(ab);
-			}
 		}
-		context->loginuid = loginuid;
 	}
+	task->loginuid = loginuid;
 	return 0;
 }
 
-/**
- * audit_get_loginuid - get the loginuid for an audit_context
- * @ctx: the audit_context
- *
- * Returns the context's loginuid or -1 if @ctx is NULL.
- */
-uid_t audit_get_loginuid(struct task_struct *task)
-{
-	struct audit_context *ctx = task->audit_context;
-	return ctx ? ctx->loginuid : -1;
-}
-
-EXPORT_SYMBOL(audit_get_loginuid);
-
 /**
  * __audit_mq_open - record audit data for a POSIX MQ open
  * @oflag: open flag
@@ -2217,8 +2191,8 @@ int __audit_signal_info(int sig, struct task_struct *t)
 	if (audit_pid && t->tgid == audit_pid) {
 		if (sig == SIGTERM || sig == SIGHUP || sig == SIGUSR1) {
 			audit_sig_pid = tsk->pid;
-			if (ctx)
+			if (tsk->loginuid != -1)
-				audit_sig_uid = ctx->loginuid;
+				audit_sig_uid = tsk->loginuid;
 			else
 				audit_sig_uid = tsk->uid;
 			selinux_get_task_sid(tsk, &audit_sig_sid);