crash with SIGSEGV in __GI___strdup()

Question

I write code to read and open myapp configuration from xml file. Code attempt to parse the file for key elements and create them if they don't exist:

static xmlDocPtr configsave_open( const char *config_filename )
{
    xmlDocPtr doc;
    xmlNodePtr top;
    int create_file = 0;

    doc = xmlParseFile( config_filename );
    ......................................
    xmlKeepBlanksDefault( 0 );

    if( create_file ) {
        char *temp = strdup( config_filename ); /* <-- crashed with SIGSEGV in __GI___strdup() */

        if( ! temp ) {
            fprintf( stderr, "strdup failed for config_filename %s\n", config_filename );
            xmlFreeDoc( doc );
            return 0;
        }

        mkdir_and_force_owner( dirname( temp ), getuid(), getgid() );

        free( temp );
    }
    ......................................
    return doc;
}

I write testcase:

#!/bin/bash

# seed id: 16154
DIR="$( cd "$( dirname "$0" )" && pwd )"
GDB=

if [ "$1" = "-g" ]
then
    GDB="gdb --args"
fi

env -i \
    MALLOC_CHECK_=0 \
    $GDB \
/usr/bin/myapp \
    "`cat $DIR/argv_1.symb`" \
    "`cat $DIR/argv_2.symb`" \
    \
    < "$DIR/file___dev__stdin.symb"

exit_code=$?
exit $exit_code

where argv_2.symb file containe:

'`

and file__dev_stdin.symb containe:

AAAAAAAAAAAAAAAAAAAAAAAA

crash output:

I/O warning : failed to load external entity "NULL"
./exploit.sh: line 19:  7175 Segmentation fault
(core dumped)
env -i MALLOC_CHECK_=0 $GDB /usr/bin/myapp "`cat $DIR/argv_1.symb`" "`cat $DIR/argv_2.symb`" < "$DIR/file___dev__stdin.symb"

basic crash when try to run myapp with configfile args:

/usr/bin/myapp --configfile '`

Any help to solve this are welcome

Answer 1

I believe that config_filename might be NULL here, especially considering this message:

I/O warning : failed to load external entity "NULL"

If that is not the case, we probably need more context.