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POC++ strncpy parameters "optimized out"; overwrites random memory
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  1. POC++ strncpy parameters "optimized out"; overwrites random memory
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    copied!<p>First of all, I want to apologize for not being able to narrow down the problem enough to be able to share a short program that reproduces the bug.</p> <p>An external library (FUSE) call to <code>strncpy</code> "randomly" overwrites a <code>shared_ptr&lt;mutex&gt;</code> in my code, which causes a segfault when I try to lock that mutex. I ran my program with valgrind and it didn't catch any memory errors (valgrind flags below). When I run my code in gdb and set a watchpoint on that <code>shared_ptr</code>, it breaks on the call to strncpy. gdb says that all of <code>strncpy</code>'s parameters (dest, src, and nbytes) have been "optimized out", which makes me think it's using uninitialized memory for that call. Am I interpreting this correctly? Any idea what the cause could be?</p> <p>Here's the stack trace from gdb when the pointer is overwritten:</p> <pre><code>#0 __strncpy_ssse3 () at ../sysdeps/x86_64/multiarch/strcpy-ssse3.S:2482 #1 0x0000003245809094 in strncpy (__len=&lt;optimized out&gt;, __src=&lt;optimized out&gt;, __dest=&lt;optimized out&gt;) at /usr/include/bits/string3.h:120 #2 add_name (buf=&lt;optimized out&gt;, bufsize=&lt;optimized out&gt;, s=&lt;optimized out&gt;, name=&lt;optimized out&gt;) at fuse.c:907 #3 0x000000324580997c in try_get_path (f=&lt;optimized out&gt;, nodeid=&lt;optimized out&gt;, name=&lt;optimized out&gt;, path=&lt;optimized out&gt;, wnodep=&lt;optimized out&gt;, need_lock=&lt;optimized out&gt;) at fuse.c:956 #4 0x000000324580a281 in get_path_common (f=&lt;optimized out&gt;, nodeid=&lt;optimized out&gt;, name=&lt;optimized out&gt;, path=&lt;optimized out&gt;, wnode=&lt;optimized out&gt;) at fuse.c:1152 #5 0x0000003245812432 in fuse_lib_unlink (req=&lt;optimized out&gt;, parent=&lt;optimized out&gt;, name=&lt;optimized out&gt;) at fuse.c:1198 #6 0x0000003245817057 in fuse_ll_process_buf (data=0x6f5650, buf=0x7fffffffd850, ch=&lt;optimized out&gt;) at fuse_lowlevel.c:2441 #7 0x000000324581388f in fuse_session_loop (se=0x6f8410) at fuse_loop.c:40 #8 0x000000324580b698 in fuse_loop (f=&lt;optimized out&gt;) at fuse.c:4309 #9 0x000000324581bb8f in fuse_main_common (argc=&lt;optimized out&gt;, argv=&lt;optimized out&gt;, op=&lt;optimized out&gt;, op_size=&lt;optimized out&gt;, user_data=&lt;optimized out&gt;, compat=&lt;optimized out&gt;) at helper.c:355 #10 0x000000000046f1b6 in main (argc=4, argv=0x7fffffffdec8) at ../src/fuse.cpp:100 </code></pre> <p>Here's the arguments I ran valgrind with:</p> <pre><code>valgrind --tool=memcheck --leak-check=yes --show-reachable=yes --num-callers=20 --track-fds=yes </code></pre>
 

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