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/*
* No copyright is claimed. This code is in the public domain; do with
* it what you wish.
*
* Authors: Christian Goeschel Ndjomouo <cgoesc2@wgu.edu> [2025]
*/
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include <sys/types.h>
#include <errno.h>
#include <err.h>
#include "c.h"
#include "nls.h"
#include "strutils.h"
#include "pidfd-utils.h"
#include "statfs_magic.h"
/*
* Returns 1, if the pidfd has the pidfs file system type, otherwise 0.
*/
int pfd_is_pidfs(int pidfd)
{
struct statfs stfs;
int rc;
rc = fstatfs(pidfd, &stfs);
if (rc < 0)
return 0;
return F_TYPE_EQUAL(stfs.f_type, STATFS_PIDFS_MAGIC);
}
#ifdef USE_PIDFD_INO_SUPPORT
uint64_t pidfd_get_inode(int pidfd)
{
struct statx stx;
int rc;
rc = statx(pidfd, "", AT_EMPTY_PATH, STATX_INO, &stx);
if (rc < 0) {
close(pidfd);
err(EXIT_FAILURE, N_("failed to statx() pidfd"));
}
return stx.stx_ino;
}
#endif
/*
* ul_get_valid_pidfd_or_err() - Return a valid file descriptor for a PID
* or exit the process with an error message.
*
* @pid: PID number for which to get a file descriptor
* @pfd_ino: A pidfd inode number that is expected to be the
* same as for the new file descriptor.
*
* Pass @pfd_ino as 0, if the pidfd should not be validated.
*
* Return: On success, a file descriptor is returned.
* On failure, err() is called with an error message
* and the processes is terminated.
*
*/
#ifdef USE_PIDFD_INO_SUPPORT
int ul_get_valid_pidfd_or_err(pid_t pid, uint64_t pidfd_ino)
#else
int ul_get_valid_pidfd_or_err(pid_t pid, uint64_t pidfd_ino __attribute__((__unused__)))
#endif
{
int pfd;
pfd = ul_get_valid_pidfd(pid, pidfd_ino);
if (pfd < 0)
err(EXIT_FAILURE, N_("failed to obtain a valid file descriptor for PID %d"), pid);
return pfd;
}
/*
* ul_get_valid_pidfd() - Return a valid file descriptor for a PID
*
* @pid: PID number for which to get a file descriptor
* @pfd_ino: A pidfd inode number that is expected to be the
* same as for the new file descriptor.
*
* Pass @pfd_ino as 0, if the pidfd should not be validated.
*
* Return: On success, a file descriptor is returned.
* On failure, a negative errno is returned and errno
* is set accordingly.
*
*/
#ifdef USE_PIDFD_INO_SUPPORT
int ul_get_valid_pidfd(pid_t pid, uint64_t pidfd_ino)
#else
int ul_get_valid_pidfd(pid_t pid, uint64_t pidfd_ino __attribute__((__unused__)))
#endif
{
int pfd;
pfd = pidfd_open(pid, 0);
if (pfd < 0)
return -errno;
/* the file descriptor has to have the pidfs file system type
* otherwise the inode assigned to it will not be useful.
*/
if (!pfd_is_pidfs(pfd)) {
close(pfd);
return -(errno = ENOTSUP);
}
#ifdef USE_PIDFD_INO_SUPPORT
uint64_t real_pidfd_ino;
if (pidfd_ino) {
real_pidfd_ino = pidfd_get_inode(pfd);
if (real_pidfd_ino != pidfd_ino) {
close(pfd);
return -(errno = ESRCH);
}
}
#endif
return pfd;
}
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