From 6b18dfd626f3b43114a8068d20536b996d90c319 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Rafa=C5=82=20Harabie=C5=84?= <rafalh1992@o2.pl>
Date: Sat, 23 Sep 2017 00:22:31 +0200
Subject: [PATCH] Don't read past end of file.

---
 src/dir.rs  | 26 ++++++++++++++++----------
 src/file.rs | 10 ++++++++--
 src/fs.rs   | 17 ++++++++++++-----
 3 files changed, 36 insertions(+), 17 deletions(-)

diff --git a/src/dir.rs b/src/dir.rs
index 8dc91c5..9fed0e8 100644
--- a/src/dir.rs
+++ b/src/dir.rs
@@ -84,21 +84,27 @@ impl FatDirEntry {
 
 impl<T: Read+Seek> FatFileSystem<T> {
     pub fn read_dir(&mut self, dir: &mut FatFile) -> io::Result<Vec<FatDirEntry>> {
-        
-        let mut cur = Cursor::new(vec![0; 512]);
-        self.read(dir, cur.get_mut())?;
-        
         let mut entries = Vec::new();
+        let mut buf = vec![0; self.get_cluster_size() as usize];
         loop {
-            let entry = read_dir_entry(&mut cur)?;
-            if entry.name[0] == 0 {
-                break; // end of dir
+            let size = self.read(dir, &mut buf)?;
+            if size == 0 {
+                break;
             }
-            if entry.name[0] == 0xE5 {
-                continue; // deleted
+            
+            let mut cur = Cursor::new(&buf[..size]);
+            loop {
+                let entry = read_dir_entry(&mut cur)?;
+                if entry.name[0] == 0 {
+                    break; // end of dir
+                }
+                if entry.name[0] == 0xE5 {
+                    continue; // deleted
+                }
+                entries.push(entry);
             }
-            entries.push(entry);
         }
+        
         Ok(entries)
     }
 }
diff --git a/src/file.rs b/src/file.rs
index 59a8d80..f599f84 100644
--- a/src/file.rs
+++ b/src/file.rs
@@ -1,4 +1,6 @@
+use std::cmp;
 use std::io::prelude::*;
+use std::io::SeekFrom;
 use std::io;
 
 use fs::FatFileSystem;
@@ -27,8 +29,12 @@ impl<T: Read+Seek> FatFileSystem<T> {
     }
     
     pub fn read(&mut self, file: &mut FatFile, buf: &mut [u8]) -> io::Result<usize> {
-        self.seek_to_sector(file.first_sector as u64)?;
-        let size = self.rdr.read(buf)?;
+        let offset = self.offset_from_sector(file.first_sector) + file.offset as u64;
+        let mut read_size = cmp::min((file.size - file.offset) as usize, buf.len());
+        // FIXME: allow only one cluster for now
+        read_size = cmp::min(read_size, (self.get_cluster_size() - file.offset) as usize);
+        self.rdr.seek(SeekFrom::Start(offset))?;
+        let size = self.rdr.read(&mut buf[..read_size])?;
         file.offset += size as u32;
         Ok(size)
     }
diff --git a/src/fs.rs b/src/fs.rs
index 54fcd5c..ebe78d4 100644
--- a/src/fs.rs
+++ b/src/fs.rs
@@ -1,5 +1,5 @@
 use std::io::prelude::*;
-use std::io::{Error, ErrorKind, SeekFrom};
+use std::io::{Error, ErrorKind};
 use std::io;
 use std::str;
 use byteorder::{LittleEndian, ReadBytesExt};
@@ -189,15 +189,22 @@ impl<T: Read+Seek> FatFileSystem<T> {
         Ok(boot)
     }
     
-    pub fn seek_to_sector(&mut self, sector: u64) -> io::Result<()> {
-        self.rdr.seek(SeekFrom::Start(sector*512))?;
-        Ok(())
+    // pub(crate) fn offset_from_cluster(&self, cluser: u32) -> u64 {
+    //     self.offset_from_sector(self.sector_from_cluster(cluser))
+    // }
+    
+    pub(crate) fn offset_from_sector(&self, sector: u32) -> u64 {
+        (sector as u64) * self.boot.bpb.bytes_per_sector as u64
     }
     
-    pub fn sector_from_cluster(&self, cluster: u32) -> u32 {
+    pub(crate) fn sector_from_cluster(&self, cluster: u32) -> u32 {
         ((cluster - 2) * self.boot.bpb.sectors_per_cluster as u32) + self.first_data_sector
     }
     
+    pub(crate) fn get_cluster_size(&self) -> u32 {
+        self.boot.bpb.sectors_per_cluster as u32 * self.boot.bpb.bytes_per_sector as u32
+    }
+    
     pub(crate) fn get_root_dir_sector(&self) -> u32 {
         match self.fat_type {
             FatType::Fat12 | FatType::Fat16 => self.first_data_sector - self.root_dir_sectors,