Problem - Kevin Tafuro

Especially if you use the code from Recipe 1.1 to sanitize the environment, or if you
use the code from the previous subsection, you should use spc_delenv( ) to delete an
environment variable. The following code for spc_delenv( ) depends on the static
variable spc_environ declared at global scope in the spc_putenv( ) code from the previous
subsection; the two functions should share the same instance of that variable.
Note that the following code is not thread-safe. You need to explicitly avoid the possibility
of manipulating the environment from two separate threads at the same time.
#include
#include
int spc_delenv(const char *name) {
int del = 0, envc, i, idx = -1;
size_t delsz = 0, envsz = 0, namelen;
char *envptr, **new_environ;
extern int spc_environ;
extern char **environ;
/* first compute the size of the new environment */
namelen = strlen(name);
for (envc = 0; environ[envc]; envc++) {
if (!strncmp(environ[envc], name, namelen) && environ[envc][namelen] = = '=') {
if (idx = = -1) idx = envc;
else {
del++;
delsz += strlen(environ[envc]) + 1;
}
}
envsz += strlen(environ[envc]) + 1;
}
if (idx = = -1) return 1;
envc -= del; /* account for duplicate entries of the same name */
envsz -= delsz;
/* allocate memory for the new environment */
envsz += (sizeof(char *) * (envc + 1));
if (!(new_environ = (char **)malloc(envsz))) return 0;
envptr = (char *)new_environ + (sizeof(char *) * (envc + 1));
/* copy the old environment into the new environment, ignoring any
* occurrences of the environment variable that we want to delete.
*/
for (envc = i = 0; environ[envc]; envc++) {
if (envc = = idx || (del && !strncmp(environ[envc], name, namelen) &&
environ[envc][namelen] = = '=')) continue;
new_environ[i++] = envptr;
envsz = strlen(environ[envc]);
memcpy(envptr, environ[envc], envsz + 1);
envptr += (envsz + 1);
}
/* possibly free the old environment, then replace it with the new one */
96 | Chapter 3: Input Validation
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