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Issue created by <a href="https://gitlab.rtems.org/physwkim">Sang Woo Kim</a>: <a href="https://gitlab.rtems.org/rtems/rtos/rtems/-/work_items/5669">#5669</a>
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<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial">Found while testing descriptor duplication for an EPICS IOC, measured on arm/xilinx_zynq_a9_qemu.</p>
<p dir="auto" style="color: #3a383f; margin: 0px 0px 1rem;" align="initial"><code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">dup2()</code> in <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">cpukit/libcsupport/src/dup2.c</code> runs <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">fstat( fildes2, &buf )</code> before doing anything and returns the failure, so duplicating onto a descriptor that is not open — the canonical POSIX use of dup2(), which specifies that an unopen fildes2 is simply not closed — always fails:</p>
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<pre data-canonical-lang="c" class="code highlight js-syntax-highlight language-c" v-pre="true" style="display: block; font-size: 14px; color: #3a383f; line-height: 1.6em; overflow-x: auto; border-radius: .25rem; position: relative; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: break-all; word-wrap: break-word; background-color: #fbfafd; margin: 0px 0 1rem; padding: 12px; border: 1px solid #dcdcde;"><code style="font-size: inherit; color: inherit; word-wrap: normal; word-break: keep-all; background-color: inherit; border-radius: .25rem; white-space: pre; margin-top: 0px; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; overflow-wrap: normal; padding: unset;"><span id="LC1" class="line" lang="c" style="margin-top: 0px;"><span class="kt" style="margin-top: 0px;">int</span> <span class="n">s</span> <span class="o">=</span> <span class="n">socket</span><span class="p">(</span><span class="n">AF_INET</span><span class="p">,</span> <span class="n">SOCK_DGRAM</span><span class="p">,</span> <span class="mi">0</span><span class="p">);</span></span>
<span id="LC2" class="line" lang="c"><span class="kt" style="margin-top: 0px;">int</span> <span class="n">f</span> <span class="o">=</span> <span class="n">open</span><span class="p">(</span><span class="s">"/tmp-probe"</span><span class="p">,</span> <span class="n">O_CREAT</span> <span class="o">|</span> <span class="n">O_RDWR</span><span class="p">,</span> <span class="mo">0644</span><span class="p">);</span></span>
<span id="LC3" class="line" lang="c"><span class="n" style="margin-top: 0px;">close</span><span class="p">(</span><span class="n">f</span><span class="p">);</span></span>
<span id="LC4" class="line" lang="c"><span class="n" style="margin-top: 0px;">dup2</span><span class="p">(</span><span class="n">s</span><span class="p">,</span> <span class="n">f</span><span class="p">);</span> <span class="cm">/* -1, errno = EBADF */</span></span></code></pre>
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<p dir="auto" style="color: #3a383f; margin: 0px;" align="initial">POSIX only requires EBADF when fildes2 is outside the valid descriptor range, so the pre-check should be a range check, not fstat. Note that removing the pre-check alone is not enough: the underlying <code style="font-size: 90%; color: #18171d; word-wrap: break-word; background-color: #ececef; border-radius: .25rem; margin-top: 0px; font-weight: inherit; overflow-wrap: break-word; white-space: break-spaces; font-family: "GitLab Mono", "JetBrains Mono", "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; font-variant-ligatures: none; word-break: keep-all; padding: 0.125rem 0.25rem;">fcntl(F_DUP2FD)</code> path cannot handle a free target descriptor either — that is the separate defect in the fcntl issue filed alongside this one.</p>
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