pe: fix for empty string table parsing in COFF files. fixes issue #502. (#503)

Author: glslang

src/pe/header.rs

@@ -1823,4 +1823,53 @@ mod tests {
         assert_eq!(header.dos_header.pe_pointer, 0x40);
         assert_eq!(header.coff_header.number_of_sections, 3);
     }
+
+    // MASM COFF file that has an empty string table
+    static EMPTY_STRING_TABLE_OBJ: [u8; 424] = [
+        0x64, 0x86, 0x03, 0x00, 0xf3, 0xcb, 0x20, 0x69, 0x02, 0x01, 0x00, 0x00, 0x09, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x2e, 0x74, 0x65, 0x78, 0x74, 0x24, 0x6d, 0x6e, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x8c, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x20, 0x00, 0x50, 0x60,
+        0x2e, 0x64, 0x61, 0x74, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x40, 0x00, 0x50, 0xc0, 0x2e, 0x64, 0x65, 0x62, 0x75,
+        0x67, 0x24, 0x53, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x74, 0x00, 0x00, 0x00,
+        0x8d, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x40, 0x00, 0x10, 0x42, 0xc3, 0x04, 0x00, 0x00, 0x00, 0xf1, 0x00, 0x00, 0x00, 0x68,
+        0x00, 0x00, 0x00, 0x2d, 0x00, 0x01, 0x11, 0x00, 0x00, 0x00, 0x00, 0x43, 0x3a, 0x5c, 0x55,
+        0x73, 0x65, 0x72, 0x73, 0x5c, 0x43, 0x6f, 0x6e, 0x74, 0x6f, 0x73, 0x6f, 0x5c, 0x77, 0x69,
+        0x6e, 0x2d, 0x6b, 0x65, 0x78, 0x70, 0x5c, 0x61, 0x63, 0x6c, 0x5f, 0x65, 0x64, 0x69, 0x74,
+        0x2e, 0x6f, 0x62, 0x6a, 0x00, 0x37, 0x00, 0x3c, 0x11, 0x03, 0x02, 0x00, 0x00, 0xd0, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0e, 0x00, 0x2a, 0x00, 0x84, 0x86, 0x00,
+        0x00, 0x4d, 0x69, 0x63, 0x72, 0x6f, 0x73, 0x6f, 0x66, 0x74, 0x20, 0x28, 0x52, 0x29, 0x20,
+        0x4d, 0x61, 0x63, 0x72, 0x6f, 0x20, 0x41, 0x73, 0x73, 0x65, 0x6d, 0x62, 0x6c, 0x65, 0x72,
+        0x00, 0x00, 0x00, 0x40, 0x63, 0x6f, 0x6d, 0x70, 0x2e, 0x69, 0x64, 0x84, 0x86, 0x03, 0x01,
+        0xff, 0xff, 0x00, 0x00, 0x03, 0x00, 0x40, 0x66, 0x65, 0x61, 0x74, 0x2e, 0x30, 0x30, 0x10,
+        0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00, 0x03, 0x00, 0x2e, 0x74, 0x65, 0x78, 0x74, 0x24,
+        0x6d, 0x6e, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x03, 0x01, 0x01, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x2e, 0x64, 0x61, 0x74, 0x61, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x00,
+        0x00, 0x03, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x2e, 0x64, 0x65, 0x62, 0x75, 0x67, 0x24, 0x53, 0x00,
+        0x00, 0x00, 0x00, 0x03, 0x00, 0x00, 0x00, 0x03, 0x01, 0x74, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x65, 0x6d, 0x70,
+        0x74, 0x79, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x20, 0x00, 0x02, 0x00,
+        0x04, 0x00, 0x00, 0x00,
+    ];
+
+    #[test]
+    fn parse_coff_with_empty_string_table() {
+        // This test verifies that a COFF file with an empty string table can be parsed
+        // The file has a string table with only the length field (4 bytes)
+        let coff = Coff::parse(&EMPTY_STRING_TABLE_OBJ).unwrap();
+
+        // Should have sections, symbols, and a minimal string table
+        assert_eq!(coff.header.number_of_sections, 3);
+        assert_eq!(coff.header.number_of_symbol_table, 9);
+        assert!(coff.strings.is_some());
+
+        // String table should be empty (only contains the length field)
+        let strings = coff.strings.unwrap();
+        assert_eq!(strings.len(), 0); // Empty string table content
+    }
 }

src/strtab.rs

@@ -105,8 +105,12 @@ impl<'a> Strtab<'a> {
     ) -> error::Result<Self> {
         let (end, overflow) = offset.overflowing_add(len);
 
+        // For COFF with an empty string table, len is zero and offset is equal to bytes.len().
+        // In this case an empty slice is returned.
+        // ELF has explicit checks for string tables with sh_size of zero.
+
         // Handle completely invalid offset
-        if offset >= bytes.len() {
+        if offset > bytes.len() {
             #[cfg(feature = "alloc")]
             return Err(error::Error::Malformed(format!(
                 "String table offset ({}) is beyond file boundary ({})",