Add Error case for PEM with headers fields

pem-rfc7468/src/decoder.rs

@@ -31,7 +31,20 @@ pub fn decode<'i, 'o>(pem: &'i [u8], buf: &'o mut [u8]) -> Result<(&'i str, &'o
     let mut out_len = 0;
 
     for line in encapsulation.encapsulated_text() {
-        out_len += Base64::decode(line?, &mut buf[out_len..])?.len();
+        let line = line?;
+        match Base64::decode(line, &mut buf[out_len..]) {
+            Err(error) => {
+                // in the case that we are decoding the first line
+                // and we error, then attribute the error to an unsupported header
+                // if a colon char is present in the line
+                if out_len == 0 && line.iter().any(|&b| b == grammar::CHAR_COLON) {
+                    return Err(Error::HeaderDetected);
+                } else {
+                    return Err(error.into());
+                }
+            }
+            Ok(out) => out_len += out.len(),
+        }
     }
 
     Ok((label, &buf[..out_len]))
@@ -154,6 +167,7 @@ impl<'a> Encapsulation<'a> {
     /// encapsulated text.
     pub fn encapsulated_text(self) -> Lines<'a> {
         Lines {
+            is_start: true,
             bytes: self.encapsulated_text,
         }
     }
@@ -169,6 +183,8 @@ impl<'a> TryFrom<&'a [u8]> for Encapsulation<'a> {
 
 /// Iterator over the lines in the encapsulated text.
 struct Lines<'a> {
+    /// true if no lines have been read
+    is_start: bool,
     /// Remaining data being iterated over.
     bytes: &'a [u8],
 }
@@ -179,13 +195,24 @@ impl<'a> Iterator for Lines<'a> {
     fn next(&mut self) -> Option<Self::Item> {
         if self.bytes.len() > BASE64_WRAP_WIDTH {
             let (line, rest) = self.bytes.split_at(BASE64_WRAP_WIDTH);
-            let result = grammar::strip_leading_eol(rest)
-                .ok_or(Error::EncapsulatedText)
-                .map(|rest| {
-                    self.bytes = rest;
-                    line
-                });
-            Some(result)
+            if let Some(rest) = grammar::strip_leading_eol(rest) {
+                self.is_start = false;
+                self.bytes = rest;
+                Some(Ok(line))
+            } else {
+                // if bytes remaining does not split at BASE64_WRAP_WIDTH such
+                // that the next char(s) in the rest is vertical whitespace
+                // then attribute the error generically as `EncapsulatedText`
+                // unless we are at the first line and the line contains a colon
+                // then it may be a unsupported header
+                Some(Err(
+                    if self.is_start && line.iter().any(|&b| b == grammar::CHAR_COLON) {
+                        Error::HeaderDetected
+                    } else {
+                        Error::EncapsulatedText
+                    },
+                ))
+            }
         } else if !self.bytes.is_empty() {
             let line = self.bytes;
             self.bytes = &[];

pem-rfc7468/src/error.rs

@@ -18,6 +18,9 @@ pub enum Error {
     /// Errors in the encapsulated text (which aren't specifically Base64-related).
     EncapsulatedText,
 
+    /// Header detected in the encapsulated text
+    HeaderDetected,
+
     /// Invalid label.
     Label,
 
@@ -37,6 +40,7 @@ impl fmt::Display for Error {
             Error::Base64 => "PEM Base64 error",
             Error::CharacterEncoding => "PEM character encoding error",
             Error::EncapsulatedText => "PEM error in encapsulated text",
+            Error::HeaderDetected => "PEM header (disallowed) detected in encapsulated text",
             Error::Label => "PEM type label invalid",
             Error::Length => "PEM length invalid",
             Error::PreEncapsulationBoundary => "PEM error in pre-encapsulation boundary",

pem-rfc7468/src/grammar.rs

@@ -19,6 +19,9 @@ pub(crate) const CHAR_CR: u8 = 0x0d;
 /// Line feed
 pub(crate) const CHAR_LF: u8 = 0x0a;
 
+/// Colon ':'
+pub(crate) const CHAR_COLON: u8 = 0x3A;
+
 /// Does the provided byte match a character allowed in a label?
 // TODO(tarcieri): relax this to match the RFC 7468 ABNF
 pub(crate) fn is_labelchar(char: u8) -> bool {

pem-rfc7468/tests/decode.rs

@@ -9,6 +9,26 @@ fn pkcs1_example() {
     assert_eq!(decoded, include_bytes!("examples/pkcs1.der"));
 }
 
+#[test]
+fn pkcs1_enc_example() {
+    let pem = include_bytes!("examples/ssh_rsa_pem_password.pem");
+    let mut buf = [0u8; 2048];
+    match pem_rfc7468::decode(pem, &mut buf) {
+        Err(pem_rfc7468::Error::HeaderDetected) => (),
+        _ => panic!("Expected HeaderDetected error"),
+    }
+}
+
+#[test]
+fn header_of_length_64() {
+    let pem = include_bytes!("examples/chosen_header.pem");
+    let mut buf = [0u8; 2048];
+    match pem_rfc7468::decode(pem, &mut buf) {
+        Err(pem_rfc7468::Error::HeaderDetected) => (),
+        _ => panic!("Expected HeaderDetected error"),
+    }
+}
+
 #[test]
 fn pkcs8_example() {
     let pem = include_bytes!("examples/pkcs8.pem");

pem-rfc7468/tests/examples/chosen_header.pem

@@ -0,0 +1,31 @@
+-----BEGIN RSA PRIVATE KEY-----
+A-Header-That-Happens-To-Be-Exactly: 64 characters long.........
+Proc-Type: 4,ENCRYPTED
+DEK-Info: AES-128-CBC,15670D76FD184D46C40C971733E0543F
+
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+LTy2VS0p3QuUeMnNRl0HxpB16BZax9mzFr0UvFKp2QQYzOkIghg2sLNEbtaJvHNh
+-----END RSA PRIVATE KEY-----

pem-rfc7468/tests/examples/ssh_rsa_pem_password.pem

@@ -0,0 +1,30 @@
+-----BEGIN RSA PRIVATE KEY-----
+Proc-Type: 4,ENCRYPTED
+DEK-Info: AES-128-CBC,15670D76FD184D46C40C971733E0543F
+
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+-----END RSA PRIVATE KEY-----