From 2d9b7ce6443cdce1209cd85364cb05a448bad89e Mon Sep 17 00:00:00 2001
From: Jonas Konrad <me@yawk.at>
Date: Fri, 25 Sep 2026 17:26:56 +0200
Subject: [PATCH] Throw IOException for invalid or unsupported frame
 descriptors

LZ4FrameInputStream.readHeader() passed the FLG and BD bytes to
FLG.fromByte/BD.fromByte unguarded, so reserved bits, dependent blocks,
dictionary IDs, bad versions and invalid block size indicators surfaced
as RuntimeException/IllegalArgumentException from read(), skip() and
the expected content size getters. Wrap them in an IOException instead.

Fixes #102

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 .../net/jpountz/lz4/LZ4FrameInputStream.java  | 13 ++++--
 .../net/jpountz/lz4/LZ4FrameIOStreamTest.java | 43 +++++++++++++++++++
 2 files changed, 53 insertions(+), 3 deletions(-)

diff --git a/src/java/net/jpountz/lz4/LZ4FrameInputStream.java b/src/java/net/jpountz/lz4/LZ4FrameInputStream.java
index 728524de..2ffed01b 100644
--- a/src/java/net/jpountz/lz4/LZ4FrameInputStream.java
+++ b/src/java/net/jpountz/lz4/LZ4FrameInputStream.java
@@ -46,6 +46,7 @@ public class LZ4FrameInputStream extends FilterInputStream {
   static final String NOT_SUPPORTED = "Stream unsupported";
   static final String BLOCK_HASH_MISMATCH = "Block checksum mismatch";
   static final String DESCRIPTOR_HASH_MISMATCH = "Stream frame descriptor corrupted";
+  static final String INVALID_DESCRIPTOR = "Invalid or unsupported frame descriptor";
   static final int MAGIC_SKIPPABLE_BASE = 0x184D2A50;
 
   private final LZ4SafeDecompressor decompressor;
@@ -193,10 +194,16 @@ private void readHeader() throws IOException {
     }
 
     final byte flgByte = (byte) (flgRead & 0xFF);
-    final LZ4FrameOutputStream.FLG flg = LZ4FrameOutputStream.FLG.fromByte(flgByte);
-    headerBuffer.put(flgByte);
     final byte bdByte = (byte) (bdRead & 0xFF);
-    final LZ4FrameOutputStream.BD bd = LZ4FrameOutputStream.BD.fromByte(bdByte);
+    final LZ4FrameOutputStream.FLG flg;
+    final LZ4FrameOutputStream.BD bd;
+    try {
+      flg = LZ4FrameOutputStream.FLG.fromByte(flgByte);
+      bd = LZ4FrameOutputStream.BD.fromByte(bdByte);
+    } catch (RuntimeException e) {
+      throw new IOException(INVALID_DESCRIPTOR, e);
+    }
+    headerBuffer.put(flgByte);
     headerBuffer.put(bdByte);
 
     this.frameInfo = new LZ4FrameOutputStream.FrameInfo(flg, bd);
diff --git a/src/test/net/jpountz/lz4/LZ4FrameIOStreamTest.java b/src/test/net/jpountz/lz4/LZ4FrameIOStreamTest.java
index dcd6607a..04623085 100644
--- a/src/test/net/jpountz/lz4/LZ4FrameIOStreamTest.java
+++ b/src/test/net/jpountz/lz4/LZ4FrameIOStreamTest.java
@@ -16,6 +16,7 @@
  * limitations under the License.
  */
 
+import net.jpountz.xxhash.XXHashFactory;
 import org.junit.After;
 import org.junit.Assert;
 import org.junit.Assume;
@@ -576,4 +577,46 @@ public void testAvailable() throws IOException {
       lz4File.delete();
     }
   }
+
+  private static byte[] frameHeader(int flg, int bd) {
+    final byte[] descriptor = new byte[]{(byte) flg, (byte) bd};
+    final byte hc = (byte) ((XXHashFactory.fastestInstance().hash32().hash(descriptor, 0, descriptor.length, 0) >> 8) & 0xFF);
+    final ByteBuffer header = ByteBuffer.allocate(7).order(ByteOrder.LITTLE_ENDIAN);
+    header.putInt(LZ4FrameOutputStream.MAGIC);
+    header.put(descriptor);
+    header.put(hc);
+    return header.array();
+  }
+
+  private static void assertInvalidDescriptor(IOException e) {
+    Assert.assertEquals(LZ4FrameInputStream.INVALID_DESCRIPTOR, e.getMessage());
+  }
+
+  @Test
+  public void testInvalidOrUnsupportedFrameDescriptor() throws IOException {
+    Assume.assumeTrue(testSize == 0); // does not depend on the test size
+    final int[][] descriptors = {
+        {0x40, 0x70}, // dependent blocks
+        {0x61, 0x70}, // dictionary ID
+        {0x62, 0x70}, // reserved FLG bit
+        {0x20, 0x70}, // unsupported version
+        {0x60, 0x30}, // block size indicator 3
+        {0x60, 0x41}, // reserved BD bit
+    };
+    for (final int[] d : descriptors) {
+      final byte[] header = frameHeader(d[0], d[1]);
+      try (InputStream is = new LZ4FrameInputStream(new ByteArrayInputStream(header))) {
+        assertInvalidDescriptor(Assert.assertThrows(IOException.class, is::read));
+      }
+      try (InputStream is = new LZ4FrameInputStream(new ByteArrayInputStream(header))) {
+        assertInvalidDescriptor(Assert.assertThrows(IOException.class, () -> is.skip(1)));
+      }
+      try (LZ4FrameInputStream is = new LZ4FrameInputStream(new ByteArrayInputStream(header), true)) {
+        assertInvalidDescriptor(Assert.assertThrows(IOException.class, is::getExpectedContentSize));
+      }
+      try (LZ4FrameInputStream is = new LZ4FrameInputStream(new ByteArrayInputStream(header), true)) {
+        assertInvalidDescriptor(Assert.assertThrows(IOException.class, is::isExpectedContentSizeDefined));
+      }
+    }
+  }
 }