Modified the validation for ascii tag type

src/decoder/ifd.rs

@@ -4,6 +4,7 @@ use std::collections::HashMap;
 use std::convert::{TryFrom, TryInto};
 use std::io::{self, Read, Seek};
 use std::mem;
+use std::str;
 
 use super::stream::{ByteOrder, EndianReader, SmartReader};
 use crate::tags::{Tag, Type};
@@ -420,9 +421,13 @@ impl Entry {
                 Type::ASCII => {
                     let mut buf = vec![0; self.count as usize];
                     self.r(bo).read_exact(&mut buf)?;
-                    let v = String::from_utf8(buf)?;
+                    if buf.is_ascii() && buf.ends_with(&[0]) {
+                        let v = str::from_utf8(&buf)?;
                         let v = v.trim_matches(char::from(0));
                         return Ok(Ascii(v.into()));
+                    } else {
+                        return Err(TiffError::FormatError(TiffFormatError::InvalidTag));
+                    }
                 }
                 Type::UNDEFINED => {
                     return Ok(List(

src/error.rs

@@ -1,6 +1,7 @@
 use std::error::Error;
 use std::fmt;
 use std::io;
+use std::str;
 use std::string;
 
 use crate::decoder::ifd::Value;
@@ -246,6 +247,12 @@ impl From<io::Error> for TiffError {
     }
 }
 
+impl From<str::Utf8Error> for TiffError {
+    fn from(_err: str::Utf8Error) -> TiffError {
+        TiffError::FormatError(TiffFormatError::InvalidTag)
+    }
+}
+
 impl From<string::FromUtf8Error> for TiffError {
     fn from(_err: string::FromUtf8Error) -> TiffError {
         TiffError::FormatError(TiffFormatError::InvalidTag)