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POPreventing a routine that deletes a set of files from being destructive
 

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  1. POPreventing a routine that deletes a set of files from being destructive
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    <p>The following is a small excerpt of a program I have written. The routine goes through <code>filenamelist</code> (permission 0600) which contains a list of line separated file names stored that are all stored in <code>directory</code> (like <code>FileOne\nAnotherFile\nThird file\n</code>) with the file extension <code>EXTENSION</code>. The list of file names comes from another part of my program.</p> <p>I am a bit afraid that the <code>filenamelist</code> can be abused to delete other files on the system. Is there a better way of locking it down? Originally I stored the full path to the files that where to be deleted, but later separated and hardcoded the directory and file extension in an attempt to obfuscate it.</p> <p>I am possibly being paranoid, but a malicious user (!) could poison the <code>filenamelist</code> with other file paths, somehow. For example <code>../../another-directory/donotdeleteme.sys</code> or escape it someway that I cannot even think of.</p> <p>So can the below deletion routine be misused to delete files outside <code>directory</code>? Any suggestions on how I can lock it down further to prevent cat·astrophe?</p> <p>PS: The program must <em>run as root</em> as part of it’s operation is modifying files outside the user’s home directory.</p> <pre><code>#define EXTENSION ".stuff" char *directory = calloc( 28 ); directory = "/usr/local/share/stuffings/"; char *filenamelist = calloc( 24 ); filenamelist = "/etc/stuffing/files.lst"; void delete_files( char* filenamelist, char* directory ) { if ( access( filenamelist, F_OK | R_OK ) == 0 ) { FILE *filenamelist_fp = fopen( filenamelist, "r" ); char filename[200]; while( fgets( filename, 200, filenamelist_fp ) != NULL ) { char *pos; char *path = calloc( ( strlen( directory ) + strlen( filename ) + strlen( EXTENSION ) + 1 ), sizeof( char ) ); if ( ( pos=strchr( filename, '\n' ) ) != NULL ) *pos = '\0'; strcat( path, directory ); strcat( path, filename ); strcat( path, EXTENSION ); if ( access( path, F_OK | W_OK ) == 0 ) unlink( path ); free( path ); } fclose( filenamelist_fp ); unlink( filenamelist ); } } /* © */ </code></pre>
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    1. USAeyoun
    1. USAeyoun
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    1. CO`filenamelist = "/etc/stuffing/files.lst";` loses the handle to the memory you `calloc`ed the line before. You probably meant something like `strcpy(filenamelist, "/etc/...");`.
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      1. POPreventing a routine that deletes a set of files from being destructive
      1. USDaniel Fischer
    2. COPlease note that in unix '\n' is a valid character in filenames. Also: you could remember the sizes and use snprintf() instead of the strcat(). And the access() is useless, IMHO. And: to unlink a file you must have write access to the directory, which you don't check. And what Daniel says the same for dirname.
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      1. POPreventing a routine that deletes a set of files from being destructive
      1. USwildplasser
    3. CONever try security through obscurity. It's a bad idea that almost never works. Instead, do proven things like sandboxing, encryption, etc.
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      1. POPreventing a routine that deletes a set of files from being destructive
      1. USLinuxios
 

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