From 03b6b891c4cfe0eb29e0196efcb6d23a728986d7 Mon Sep 17 00:00:00 2001
From: Codex <codex@noreply.local>
Date: Thu, 28 May 2026 10:33:46 +0000
Subject: [PATCH] fix: harden apply-patch v2 remote reads

---
 scripts/src/apply-patch-v2.ts | 58 +++++++++++++++++++++++++++++++++--
 1 file changed, 55 insertions(+), 3 deletions(-)

diff --git a/scripts/src/apply-patch-v2.ts b/scripts/src/apply-patch-v2.ts
index 37dc4dd6..89a9992f 100644
--- a/scripts/src/apply-patch-v2.ts
+++ b/scripts/src/apply-patch-v2.ts
@@ -281,6 +281,7 @@ async function executePlannedOperation(executor: ApplyPatchV2Executor, operation
 const readBlockBytes = 45_000;
 const writeB64ArgvLimit = 48_000;
 const writeB64ChunkChars = 12_000;
+const remoteReadBlockMarker = "UNIDESK_APPLY_PATCH_V2_BLOCK";
 
 async function readRemoteText(executor: ApplyPatchV2Executor, target: string): Promise<string> {
   if (executor.fs) {
@@ -333,8 +334,8 @@ async function readRemoteText(executor: ApplyPatchV2Executor, target: string): P
   let actualBytes = 0;
   for (let blockIndex = 0; actualBytes < expectedBytes; blockIndex += 1) {
     const read = await checkedRemoteV2(executor, "read-b64-block", [target, String(blockIndex), String(readBlockBytes)]);
-    const encoded = read.stdout.replace(/\s+/gu, "");
-    const chunk = encoded.length === 0 ? Buffer.alloc(0) : Buffer.from(encoded, "base64");
+    const expectedChunkBytes = Math.min(readBlockBytes, expectedBytes - actualBytes);
+    const chunk = decodeRemoteReadBlock(read.stdout, target, blockIndex, expectedChunkBytes);
     if (chunk.length === 0) {
       throw new ApplyPatchV2Error("remote apply-patch v2 read returned an empty block before EOF", {
         path: target,
@@ -366,6 +367,50 @@ async function readRemoteText(executor: ApplyPatchV2Executor, target: string): P
   return contentBuffer.toString("utf8");
 }
 
+function decodeRemoteReadBlock(stdout: string, target: string, blockIndex: number, expectedChunkBytes: number): Buffer {
+  const lines = stdout.split(/\r?\n/u);
+  const markerIndex = lines.findIndex((line) => line.startsWith(`${remoteReadBlockMarker} `));
+  let encoded = "";
+  let declaredBytes: number | null = null;
+  let declaredSha256: string | null = null;
+  if (markerIndex >= 0) {
+    const [, bytesText, sha256] = lines[markerIndex].split(/\s+/u);
+    declaredBytes = Number(bytesText);
+    declaredSha256 = sha256 ?? null;
+    if (!Number.isSafeInteger(declaredBytes) || declaredBytes < 0 || !/^[0-9a-f]{64}$/u.test(declaredSha256 ?? "")) {
+      throw new ApplyPatchV2Error("remote apply-patch v2 read block returned invalid metadata", {
+        path: target,
+        blockIndex,
+        marker: lines[markerIndex].slice(0, 200),
+      });
+    }
+    encoded = (lines[markerIndex + 1] ?? "").replace(/\s+/gu, "");
+  } else {
+    encoded = stdout.replace(/\s+/gu, "");
+  }
+  const decoded = encoded.length === 0 ? Buffer.alloc(0) : Buffer.from(encoded, "base64");
+  if (declaredBytes !== null) {
+    if (decoded.length !== declaredBytes) {
+      throw new ApplyPatchV2Error("remote apply-patch v2 read block byte count mismatch", {
+        path: target,
+        blockIndex,
+        expectedBytes: declaredBytes,
+        actualBytes: decoded.length,
+      });
+    }
+    const actualSha256 = sha256Hex(decoded);
+    if (actualSha256 !== declaredSha256) {
+      throw new ApplyPatchV2Error("remote apply-patch v2 read block sha256 mismatch", {
+        path: target,
+        blockIndex,
+        expectedSha256: declaredSha256,
+        actualSha256,
+      });
+    }
+  }
+  return decoded.length > expectedChunkBytes ? decoded.subarray(0, expectedChunkBytes) : decoded;
+}
+
 async function writeRemoteText(executor: ApplyPatchV2Executor, target: string, content: string): Promise<void> {
   const contentBuffer = Buffer.from(content, "utf8");
   if (executor.fs) {
@@ -473,7 +518,14 @@ function remoteV2Script(operation: RemoteV2Operation, args: string[]): string[]
     "    block_index=$2",
     "    block_size=$3",
     "    case \"$block_index:$block_size\" in *[!0-9:]*|:*) printf 'invalid read block args\\n' >&2; exit 2;; esac",
-    "    dd if=\"$target\" bs=\"$block_size\" skip=\"$block_index\" count=1 2>/dev/null | base64 | tr -d '\\n'",
+    "    tmp=$(mktemp)",
+    "    dd if=\"$target\" bs=\"$block_size\" skip=\"$block_index\" count=1 2>/dev/null > \"$tmp\"",
+    "    bytes=$(wc -c < \"$tmp\" | tr -d '[:space:]')",
+    "    digest=$(sha256_file \"$tmp\")",
+    `    printf '${remoteReadBlockMarker} %s %s\\n' "$bytes" "$digest"`,
+    "    base64 < \"$tmp\" | tr -d '\\n'",
+    "    printf '\\n'",
+    "    rm -f -- \"$tmp\"",
     "    ;;",
     "  write-b64-argv)",
     "    target=$1",