From dc425fc3e89188d0b720086f06cb0d812ec34598 Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Thu, 21 Dec 2023 14:04:34 +0100
Subject: [PATCH] Revert "[XPCOM] Compare return value of readlink in
 nsLocalFileUnix::GetNativeTarget"

This reverts commit 66b07ce6991160e768b5113f8adcd0b47be58791.
---
 xpcom/io/nsLocalFileUnix.cpp | 70 +++++++++++++-----------------------
 1 file changed, 24 insertions(+), 46 deletions(-)

diff --git a/xpcom/io/nsLocalFileUnix.cpp b/xpcom/io/nsLocalFileUnix.cpp
index 1f71c70566..33c6b6bfaf 100644
--- a/xpcom/io/nsLocalFileUnix.cpp
+++ b/xpcom/io/nsLocalFileUnix.cpp
@@ -1699,47 +1699,6 @@ nsLocalFile::Contains(nsIFile* aInFile, bool* aResult)
   return NS_OK;
 }
 
-static nsresult ReadLinkSafe(const nsCString& aTarget, int32_t aExpectedSize,
-                             nsACString& aOutBuffer) {
-  // If we call readlink with a buffer size S it returns S, then we cannot tell
-  // if the buffer was big enough to hold the entire path. We allocate an
-  // additional byte so we can check if the buffer was large enough.
-  const auto allocSize = CheckedInt<size_t>(aExpectedSize) + 1;
-  if (!allocSize.isValid()) {
-    return NS_ERROR_OUT_OF_MEMORY;
-  }
-
-  auto result = aOutBuffer.BulkWrite(allocSize.value(), 0, false);
-  if (result.isErr()) {
-    return result.unwrapErr();
-  }
-
-  auto handle = result.unwrap();
-
-  while (true) {
-    ssize_t bytesWritten =
-        readlink(aTarget.get(), handle.Elements(), handle.Length());
-    if (bytesWritten < 0) {
-      return NSRESULT_FOR_ERRNO();
-    }
-
-    // written >= 0 so it is safe to cast to size_t.
-    if ((size_t)bytesWritten < handle.Length()) {
-      // Target might have changed since the lstat call, or lstat might lie, see
-      // bug 1791029.
-      handle.Finish(bytesWritten, false);
-      return NS_OK;
-    }
-
-    // The buffer was not large enough, so double it and try again.
-    auto restartResult = handle.RestartBulkWrite(handle.Length() * 2, 0, false);
-    if (restartResult.isErr()) {
-      return restartResult.unwrapErr();
-    }
-  }
-}
-
-
 NS_IMETHODIMP
 nsLocalFile::GetNativeTarget(nsACString& aResult)
 {
@@ -1755,12 +1714,21 @@ nsLocalFile::GetNativeTarget(nsACString& aResult)
     return NS_ERROR_FILE_INVALID_PATH;
   }
 
+  int32_t size = (int32_t)symStat.st_size;
   nsAutoCString target;
-  nsresult rv = ReadLinkSafe(mPath, symStat.st_size, target);
-  if (NS_FAILED(rv)) {
-    return rv;
+  if (!target.SetLength(size, mozilla::fallible)) {
+    return NS_ERROR_OUT_OF_MEMORY;
   }
 
+  ssize_t written = readlink(mPath.get(), target.BeginWriting(), size_t(size));
+  if (written < 0) {
+    return NSRESULT_FOR_ERRNO();
+  }
+  // Target might have changed since the lstat call, or lstat might lie, see bug
+  // 1791029.
+  target.Truncate(written);
+
+  nsresult rv = NS_OK;
   nsCOMPtr<nsIFile> self(this);
   int32_t maxLinks = 40;
   while (true) {
@@ -1798,12 +1766,22 @@ nsLocalFile::GetNativeTarget(nsACString& aResult)
       break;
     }
 
+    int32_t newSize = (int32_t)symStat.st_size;
+    size = newSize;
     nsAutoCString newTarget;
-    rv = ReadLinkSafe(flatRetval, symStat.st_size, newTarget);
-    if (NS_FAILED(rv)) {
+    if (!newTarget.SetLength(size, mozilla::fallible)) {
+      rv = NS_ERROR_OUT_OF_MEMORY;
       break;
     }
 
+    ssize_t linkLen = readlink(flatRetval.get(), newTarget.BeginWriting(), size);
+    if (linkLen == -1) {
+      rv = NSRESULT_FOR_ERRNO();
+      break;
+    }
+    // Target might have changed since the lstat call, or lstat might lie, see bug
+    // 1791029.
+    newTarget.Truncate(linkLen);
     target = newTarget;
   }