Add fuzz target for PEM decoding

fuzz/Cargo.toml

@@ -12,6 +12,7 @@ libfuzzer-sys = "0.4"
 
 [dependencies.rustls-pki-types]
 path = ".."
+features = ["std"]
 
 # Prevent this from interfering with workspaces
 [workspace]
@@ -25,3 +26,9 @@ name = "private_key"
 path = "fuzz_targets/private_key.rs"
 test = false
 doc = false
+
+[[bin]]
+name = "pem"
+path = "fuzz_targets/pem.rs"
+test = false
+doc = false

fuzz/corpus/pem/zen.pem

@@ -0,0 +1 @@
+../../../tests/data/zen.pem

fuzz/fuzz_targets/pem.rs

@@ -0,0 +1,26 @@
+#![no_main]
+
+use std::io::Cursor;
+
+use libfuzzer_sys::fuzz_target;
+
+use rustls_pki_types::pem::PemObject;
+use rustls_pki_types::{CertificateDer, PrivateKeyDer};
+
+fuzz_target!(|data: &[u8]| {
+    // cover the code paths that use std::io
+    for x in CertificateDer::pem_reader_iter(&mut Cursor::new(data)) {
+        match x {
+            Ok(_item) => (),
+            Err(_err) => break,
+        }
+    }
+
+    // cover the code paths that use slices
+    for x in PrivateKeyDer::pem_slice_iter(data) {
+        match x {
+            Ok(_item) => (),
+            Err(_err) => break,
+        }
+    }
+});