Problem - Kevin Tafuro

if (!(new_environ = (char **)malloc(envsz))) return 0;
envptr = (char *)new_environ + (sizeof(char *) * (envc + 1));
/* copy the old environment into the new environment, replacing the named
* environment variable if it already exists; otherwise, add it at the end.
*/
for (envc = i = 0; environ[envc]; envc++) {
if (del && !strncmp(environ[envc], name, namelen) &&
environ[envc][namelen] = = '=') continue;
new_environ[i++] = envptr;
if (envc != mod) {
envsz = strlen(environ[envc]);
memcpy(envptr, environ[envc], envsz + 1);
envptr += (envsz + 1);
} else {
memcpy(envptr, name, namelen);
memcpy(envptr + namelen + 1, value, valuelen);
envptr[namelen] = '=';
envptr[namelen + valuelen + 1] = 0;
envptr += (namelen + valuelen + 1 + 1);
}
}
if (mod = = -1) {
new_environ[i++] = envptr;
memcpy(envptr, name, namelen);
memcpy(envptr + namelen + 1, value, valuelen);
envptr[namelen] = '=';
envptr[namelen + valuelen + 1] = 0;
}
new_environ[i] = 0;
/* possibly free the old environment, then replace it with the new one */
if (spc_environ) free(environ);
environ = new_environ;
spc_environ = 1;
return 1;
}
Deleting an environment variable
No method for deleting an environment variable is defined in any standard. Some
implementations of putenv( ) will delete environment variables if the assigned value
is a zero-length string. Other systems provide implementations of a function called
unsetenv( ), but it is nonstandard and thus nonportable.
None of these methods of deleting environment variables take into account the possibility
that multiple occurrences of the same environment variable may exist in the
environment. Usually, only the first occurrence will be deleted, rather than all of
them. The result is that the environment variable won’t actually be deleted because
getenv( ) will return the next occurrence of the environment variable.
Using Environment Variables Securely | 95
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