Problem - Kevin Tafuro

Discussion
execve( ) is the system call used to load and begin execution of a new program. The
other functions in the exec*( ) family are wrappers around the execve( ) system call,
and they are implemented in user space in the standard C runtime library. When a
new program is loaded and executed with execve( ), the new program replaces the
old program within the same process. As part of the process of loading the new program,
the old program’s address space is replaced with a new address space. File
descriptors that are marked to close on execute are closed; the new program inherits
all others. All other system-level properties are tied to the process, so the new program
inherits them from the old program. Such properties include the process ID,
user IDs, group IDs, working and root directories, and signal mask.
Table 1-2 lists the various exec*( ) wrappers around the execve( ) system call. Note
that many of these wrappers should not be used in secure code. In particular, never
use the wrappers that are named with a “p” suffix because they will search the environment
to locate the file to be executed. When executing external programs, you
should always specify the full path to the file that you want to execute. If the PATH
environment variable is used to locate the file, the file that is found to execute may
not be the expected one.
Table 1-2. The exec*( ) family of functions
Function signature Comments
int execl(const char *path, char *arg, ...); The argument list is terminated by a NULL. The
calling program’s environment is passed on to
the new program.
int execle(const char *path, char *arg, ...); The argument list is terminated by a NULL, and
the environment pointer to use follows immediately.
int execlp(const char *file, char *arg, ...); The argument list is terminated by a NULL. The
PATH environment variable is searched to
locate the program to execute. The calling program’s
environment is passed on to the new
program.
int exect(const char *path, const char *argv[ ],
const char *envp[ ]);
The same as execve( ), except that process
tracing is enabled.
int execv(const char *path, const char *argv[ ]); The PATH environment variable is searched to
locate the program to execute.
int execve(const char *path, const char *argv[ ],
const char *envp[ ]);
This is the main system call to load and execute
a new program.
int execvp(const char *file, const char *argv[ ]); The PATH environment variable is searched to
locate the program to execute. The calling program’s
environment is passed on to the new
program.
Executing External Programs Securely | 29
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