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POHow can I update the value of a pointer by pulling the value from an ini file?
 

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  1. POHow can I update the value of a pointer by pulling the value from an ini file?
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    <p>I am trying to make a few fixes and enhancements to <a href="http://olivier.sessink.nl/jailkit/jailkit.8.html" rel="nofollow">Jailkit</a>. The source is in CVS version control so I <a href="https://github.com/MarcusEting/jailkit" rel="nofollow">cloned it to GitHub</a>.</p> <p>The way this is set up, you edit a user's home directory in <code>/etc/passwd</code> to be something like:</p> <pre><code>/home/jail/./home/username </code></pre> <p>Then the <code>getjaildir</code> function reads over that which is passed in as <code>oldhomedir</code> until it finds the first <code>/./</code> match right to left on the string and then will set <code>jaildir</code> to what is to the left of that and the <code>newhomedir</code> to everything to the right of that.</p> <p>I want to be able to override <code>jaildir</code> with the value from a configuration file - but I suck at <code>c</code> and so I am having very difficult time even setting the variables manually.</p> <p>Here is the <a href="https://github.com/MarcusEting/jailkit/blob/master/src/jk_lib.c#L183" rel="nofollow">function</a>:</p> <pre><code>/* if it returns 1 it will allocate new memory for jaildir and newhomedir * else it will return 0 */ int getjaildir(const char *oldhomedir, char **jaildir, char **newhomedir) { int i=strlen(oldhomedir); /* we will not accept /./ as jail, so we continue looking while i &gt; 4 (minimum then is /a/./ ) * we start at the end so if there are multiple /path/./path2/./path3 the user will be jailed in the most minimized path */ while (i &gt; 4) { /* DEBUG_MSG("oldhomedir[%d]=%c\n",i,oldhomedir[i]);*/ if (oldhomedir[i] == '/' &amp;&amp; oldhomedir[i-1] == '.' &amp;&amp; oldhomedir[i-2] == '/') { DEBUG_MSG("&amp;oldhomedir[%d]=%s\n",i,&amp;oldhomedir[i]); *jaildir = strndup(oldhomedir, i-2); *newhomedir = strdup(&amp;oldhomedir[i]); return 1; } i--; } return 1; } </code></pre> <p>After many, many attempts at a more complex solution I tried a very simple, hard-coded variation:</p> <pre><code>int getjaildir(const char *oldhomedir, char **jaildir, char **newhomedir) { *jaildir = "/home/jail"; *newhomedir = "/home/username"; return 1; } </code></pre> <p>This compiles fine on linux but when I run it I end up getting <code>Segmentation fault (11)</code>. I read up on pointers, addresses, dereferencing, variable types, string concatenation, etc. but unfortunately I'm used to loosely typed languages so this is pretty hard. What am I doing wrong?</p> <p><strong>update</strong></p> <p>Instead of setting the values in the <code>getjaildir</code> function I am attempting to set them in the mail loop.</p> <p>At the top of the loop we have the variable definitions:</p> <pre><code> char *jaildir=NULL, *newhome=NULL, *shell=NULL; </code></pre> <p>And here is where the function to set them is called:</p> <pre><code>if (!getjaildir(pw-&gt;pw_dir, &amp;jaildir, &amp;newhome)) { syslog(LOG_ERR, "abort, failed to read the jail and the home from %s for user %s (%d)",pw-&gt;pw_dir, pw-&gt;pw_name, getuid()); exit(17); } </code></pre> <p>Can I just do this immediately afterwards to overwrite the values?</p> <pre><code>jaildir="/home/jail"; newhome="/home/testuser"; </code></pre> <p>When I try this it gives me:</p> <pre><code>*** glibc detected *** -su: munmap_chunk(): invalid pointer: 0x00000000004046ee *** </code></pre>
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    1. COyou can try gdb command to dbug the program.
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      1. POHow can I update the value of a pointer by pulling the value from an ini file?
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