binfmt_flat: don't use __put_user()

... and check the return value
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/binfmt_flat.c

@@ -138,35 +138,40 @@ static int create_flat_tables(struct linux_binprm *bprm, unsigned long arg_start
 	current->mm->start_stack = (unsigned long)sp & -FLAT_STACK_ALIGN;
 	sp = (unsigned long __user *)current->mm->start_stack;
 
-	__put_user(bprm->argc, sp++);
+	if (put_user(bprm->argc, sp++))
+		return -EFAULT;
 	if (IS_ENABLED(CONFIG_BINFMT_FLAT_ARGVP_ENVP_ON_STACK)) {
 		unsigned long argv, envp;
 		argv = (unsigned long)(sp + 2);
 		envp = (unsigned long)(sp + 2 + bprm->argc + 1);
-		__put_user(argv, sp++);
-		__put_user(envp, sp++);
+		if (put_user(argv, sp++) || put_user(envp, sp++))
+			return -EFAULT;
 	}
 
 	current->mm->arg_start = (unsigned long)p;
 	for (i = bprm->argc; i > 0; i--) {
-		__put_user((unsigned long)p, sp++);
+		if (put_user((unsigned long)p, sp++))
+			return -EFAULT;
 		len = strnlen_user(p, MAX_ARG_STRLEN);
 		if (!len || len > MAX_ARG_STRLEN)
 			return -EINVAL;
 		p += len;
 	}
-	__put_user(0, sp++);
+	if (put_user(0, sp++))
+		return -EFAULT;
 	current->mm->arg_end = (unsigned long)p;
 
 	current->mm->env_start = (unsigned long) p;
 	for (i = bprm->envc; i > 0; i--) {
-		__put_user((unsigned long)p, sp++);
+		if (put_user((unsigned long)p, sp++))
+			return -EFAULT;
 		len = strnlen_user(p, MAX_ARG_STRLEN);
 		if (!len || len > MAX_ARG_STRLEN)
 			return -EINVAL;
 		p += len;
 	}
-	__put_user(0, sp++);
+	if (put_user(0, sp++))
+		return -EFAULT;
 	current->mm->env_end = (unsigned long)p;
 
 	return 0;
@@ -998,7 +1003,8 @@ static int load_flat_binary(struct linux_binprm *bprm)
 			unsigned long __user *sp;
 			current->mm->start_stack -= sizeof(unsigned long);
 			sp = (unsigned long __user *)current->mm->start_stack;
-			__put_user(start_addr, sp);
+			if (put_user(start_addr, sp))
+				return -EFAULT;
 			start_addr = libinfo.lib_list[i].entry;
 		}
 	}