From 99938681206bc944f55e77472b6443992159822a Mon Sep 17 00:00:00 2001
From: Joshua Saxby <joshua.a.saxby@gmail.com>
Date: Thu, 5 Dec 2019 10:20:26 +0000
Subject: [PATCH] Fix a nasty bug in write(). DOn't allow writing to the
keyboard!
---
userprog/syscall_write.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/userprog/syscall_write.c b/userprog/syscall_write.c
index 9c356db..525e2cf 100644
--- a/userprog/syscall_write.c
+++ b/userprog/syscall_write.c
@@ -21,7 +21,10 @@ void syscall_write(struct intr_frame *f) {
unsigned size = *((unsigned*)((int*)f->esp + 3)); // size to write is fourth
// writing to stdout or stderr (fd in {1, 2}) is a special case
switch (fd) {
- case 1: // stdin
+ case 0: // writing to stdin (keyboard) is an error condition
+ f->eax = 0;
+ break;
+ case 1: // stdout
case 2: // stderr
write_to_console((const char*)buffer, size);
f->eax = size;
--
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