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<dt>Revision</dt> <dd><a href="http://trac.webkit.org/projects/webkit/changeset/197424">197424</a></dd>
<dt>Author</dt> <dd>dbates@webkit.org</dd>
<dt>Date</dt> <dd>2016-03-01 16:01:31 -0800 (Tue, 01 Mar 2016)</dd>
</dl>
<h3>Log Message</h3>
<pre>com.apple.WebKit.Networking.Development crashes in WebCore::formOpen()
https://bugs.webkit.org/show_bug.cgi?id=154682
<rdar://problem/23550269>
Reviewed by Brent Fulgham.
Speculative fix for a race condition when opening the stream for the next form data element.
Calling CFReadStreamOpen(s) in WebCore::openNextStream() can cause stream s to be closed and
deallocated before CFReadStreamOpen(s) returns.
When WebCore::openNextStream() is called it closes and deallocates the current stream and
then opens a new stream for the next form data element. Calling CFReadStreamOpen() in
WebCore::openNextStream() can lead to WebCore::openNextStream() being re-entered via
WebCore::formEventCallback() from another thread. One example when this can occur is when
the stream being opened has no data (i.e. WebCore::formEventCallback() is called
back with event type kCFStreamEventEndEncountered).
I have been unable to reproduce this crash. We know that it occurs from crash reports.
* platform/network/cf/FormDataStreamCFNet.cpp:
(WebCore::closeCurrentStream): Assert that we had acquired a lock to close the stream.
(WebCore::advanceCurrentStream): Assert that we had acquired a lock to advance the stream.
(WebCore::openNextStream): Acquire a lock before we open the next stream to ensure that
exactly one thread executes this critical section at a time.
(WebCore::formFinalize): Acquire a lock before we close the current stream.
(WebCore::formClose): Ditto.</pre>
<h3>Modified Paths</h3>
<ul>
<li><a href="#trunkSourceWebCoreChangeLog">trunk/Source/WebCore/ChangeLog</a></li>
<li><a href="#trunkSourceWebCoreplatformnetworkcfFormDataStreamCFNetcpp">trunk/Source/WebCore/platform/network/cf/FormDataStreamCFNet.cpp</a></li>
</ul>
</div>
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<h3>Diff</h3>
<a id="trunkSourceWebCoreChangeLog"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/ChangeLog (197423 => 197424)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/ChangeLog 2016-03-02 00:00:02 UTC (rev 197423)
+++ trunk/Source/WebCore/ChangeLog 2016-03-02 00:01:31 UTC (rev 197424)
</span><span class="lines">@@ -1,3 +1,32 @@
</span><ins>+2016-03-01 Daniel Bates <dabates@apple.com>
+
+ com.apple.WebKit.Networking.Development crashes in WebCore::formOpen()
+ https://bugs.webkit.org/show_bug.cgi?id=154682
+ <rdar://problem/23550269>
+
+ Reviewed by Brent Fulgham.
+
+ Speculative fix for a race condition when opening the stream for the next form data element.
+ Calling CFReadStreamOpen(s) in WebCore::openNextStream() can cause stream s to be closed and
+ deallocated before CFReadStreamOpen(s) returns.
+
+ When WebCore::openNextStream() is called it closes and deallocates the current stream and
+ then opens a new stream for the next form data element. Calling CFReadStreamOpen() in
+ WebCore::openNextStream() can lead to WebCore::openNextStream() being re-entered via
+ WebCore::formEventCallback() from another thread. One example when this can occur is when
+ the stream being opened has no data (i.e. WebCore::formEventCallback() is called
+ back with event type kCFStreamEventEndEncountered).
+
+ I have been unable to reproduce this crash. We know that it occurs from crash reports.
+
+ * platform/network/cf/FormDataStreamCFNet.cpp:
+ (WebCore::closeCurrentStream): Assert that we had acquired a lock to close the stream.
+ (WebCore::advanceCurrentStream): Assert that we had acquired a lock to advance the stream.
+ (WebCore::openNextStream): Acquire a lock before we open the next stream to ensure that
+ exactly one thread executes this critical section at a time.
+ (WebCore::formFinalize): Acquire a lock before we close the current stream.
+ (WebCore::formClose): Ditto.
+
</ins><span class="cx"> 2016-03-01 Michael Saboff <msaboff@apple.com>
</span><span class="cx">
</span><span class="cx"> ASSERT in platform/graphics/mac/ComplexTextController.cpp::capitalize()
</span></span></pre></div>
<a id="trunkSourceWebCoreplatformnetworkcfFormDataStreamCFNetcpp"></a>
<div class="modfile"><h4>Modified: trunk/Source/WebCore/platform/network/cf/FormDataStreamCFNet.cpp (197423 => 197424)</h4>
<pre class="diff"><span>
<span class="info">--- trunk/Source/WebCore/platform/network/cf/FormDataStreamCFNet.cpp 2016-03-02 00:00:02 UTC (rev 197423)
+++ trunk/Source/WebCore/platform/network/cf/FormDataStreamCFNet.cpp 2016-03-02 00:01:31 UTC (rev 197424)
</span><span class="lines">@@ -109,10 +109,13 @@
</span><span class="cx"> CFReadStreamRef formStream;
</span><span class="cx"> unsigned long long streamLength;
</span><span class="cx"> unsigned long long bytesSent;
</span><ins>+ Lock streamIsBeingOpenedOrClosedLock;
</ins><span class="cx"> };
</span><span class="cx">
</span><span class="cx"> static void closeCurrentStream(FormStreamFields* form)
</span><span class="cx"> {
</span><ins>+ ASSERT(form->streamIsBeingOpenedOrClosedLock.isHeld());
+
</ins><span class="cx"> if (form->currentStream) {
</span><span class="cx"> CFReadStreamClose(form->currentStream);
</span><span class="cx"> CFReadStreamSetClient(form->currentStream, kCFStreamEventNone, 0, 0);
</span><span class="lines">@@ -127,6 +130,8 @@
</span><span class="cx"> // Return false if we cannot advance the stream. Currently the only possible failure is that the underlying file has been removed or changed since File.slice.
</span><span class="cx"> static bool advanceCurrentStream(FormStreamFields* form)
</span><span class="cx"> {
</span><ins>+ ASSERT(form->streamIsBeingOpenedOrClosedLock.isHeld());
+
</ins><span class="cx"> closeCurrentStream(form);
</span><span class="cx">
</span><span class="cx"> if (form->remainingElements.isEmpty())
</span><span class="lines">@@ -176,6 +181,10 @@
</span><span class="cx">
</span><span class="cx"> static bool openNextStream(FormStreamFields* form)
</span><span class="cx"> {
</span><ins>+ // CFReadStreamOpen() can cause this function to be re-entered from another thread before it returns.
+ // One example when this can occur is when the stream being opened has no data. See <rdar://problem/23550269>.
+ LockHolder locker(form->streamIsBeingOpenedOrClosedLock);
+
</ins><span class="cx"> // Skip over any streams we can't open.
</span><span class="cx"> if (!advanceCurrentStream(form))
</span><span class="cx"> return false;
</span><span class="lines">@@ -213,7 +222,10 @@
</span><span class="cx"> ASSERT_UNUSED(stream, form->formStream == stream);
</span><span class="cx">
</span><span class="cx"> callOnMainThread([form] {
</span><del>- closeCurrentStream(form);
</del><ins>+ {
+ LockHolder locker(form->streamIsBeingOpenedOrClosedLock);
+ closeCurrentStream(form);
+ }
</ins><span class="cx"> delete form;
</span><span class="cx"> });
</span><span class="cx"> }
</span><span class="lines">@@ -281,6 +293,7 @@
</span><span class="cx"> static void formClose(CFReadStreamRef, void* context)
</span><span class="cx"> {
</span><span class="cx"> FormStreamFields* form = static_cast<FormStreamFields*>(context);
</span><ins>+ LockHolder locker(form->streamIsBeingOpenedOrClosedLock);
</ins><span class="cx">
</span><span class="cx"> closeCurrentStream(form);
</span><span class="cx"> }
</span></span></pre>
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