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POStuck on closing socket while interposing JVM through LD_PRELOAD
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  1. POStuck on closing socket while interposing JVM through LD_PRELOAD
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    copied!<p>I am interposing JVM through LD_PRELOAD variable.</p> <p>Basically, I want to build a virtual routing table (VRT). On bind() call, I modify the IP address and port parameters to my choice (which I save in VRT). Also, I add the socket descriptor (first argument to bind()) to a link list. (Till this stage, socket has a sin_family type of AF_INET6).</p> <p>Now when the socket is closed (close()), I want to delete the virtual routing table entry. So, I check to see if the socket descriptor we are trying to close is stored in the link list. If it is, it means that its records exists in VRT, so I should delete the VRT entry before closing the socket. The problem I am facing is that at this stage, the same socket descriptor has a sin_family value of 1 (I don't know what does it stand for) instead of 10 (AF_INET6, value during bind()). Moreover, I tried printing IP address and port of the socket descriptor at this stage but it was garbage.</p> <p>I do not know what I am missing.</p> <p>UPDATE: There is no problem with my code. The anomaly is appearing because of the following behavior of JVM (which I traced through strace)</p> <pre><code>9722 socket(PF_INET6, SOCK_STREAM, IPPROTO_IP) = 12 ...(receive messages)... 9722 dup2(11, 12) = 12 (?!?) 9722 close(12) = 0 </code></pre> <p>JVM duplicates another file descriptor over our socket, due to which its sin_family is not displayed properly on close(). Strange!</p>
 

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