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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [ASan] False alarm to recv/recvfrom"
href="https://llvm.org/bugs/show_bug.cgi?id=27673">27673</a>
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<th>Summary</th>
<td>[ASan] False alarm to recv/recvfrom
</td>
</tr>
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<th>Product</th>
<td>compiler-rt
</td>
</tr>
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<th>Version</th>
<td>unspecified
</td>
</tr>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>compiler-rt
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>laszio@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>ASan checks the return value of real recv/recvfrom to see if the written bytes
fit in the buffer:
<a href="https://github.com/llvm-mirror/compiler-rt/commit/c06094fbd7e254dc8ebf03f02d0e9935896829fe">https://github.com/llvm-mirror/compiler-rt/commit/c06094fbd7e254dc8ebf03f02d0e9935896829fe</a>
That works fine most of time. However, there is an exception: (from the RECV(2)
man page)
MSG_TRUNC (since Linux 2.2)
... return the real length of the packet or datagram, even when it was
longer than the passed buffer. ...
Some programs combine MSG_TRUNK, MSG_PEEK and a single-byte buffer to peek the
incoming data size without reading (much of) them. In this case, the return
value is usually longer than what's been written and ASan raises a false alarm
here.</pre>
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</p>
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