+/*
+ * 1) Timestamp files and directories
+ *
+ * Timestamp files MUST NOT be accessible to users other than root,
+ * this includes the name, metadata and the content of timestamp files
+ * and directories.
+ *
+ * Symlinks can be used to create, manipulate or delete wrong files
+ * and directories. The Implementation MUST reject any symlinks for
+ * timestamp files or directories.
+ *
+ * To avoid race conditions the implementation MUST use the same
+ * file descriptor for permission checks and do read or write
+ * write operations after the permission checks.
+ *
+ * The timestamp files MUST be opened with openat(2) using the
+ * timestamp directory file descriptor. Permissions of the directory
+ * MUST be checked before opening the timestamp file descriptor.
+ *
+ * 2) Clock sources for timestamps
+ *
+ * Timestamp files MUST NOT rely on only one clock source, using the
+ * wall clock would allow to reset the clock to an earlier point in
+ * time to reuse a timestamp.
+ *
+ * The timestamp MUST consist of multiple clocks and MUST reject the
+ * timestamp if there is a change to any clock because there is no way
+ * to differentiate between malicious and legitimate clock changes.
+ *
+ * 3) Timestamp lifetime
+ *
+ * The implementation MUST NOT use the user controlled stdin, stdout
+ * and stderr file descriptors to determine the controlling terminal.
+ * On linux the /proc/$pid/stat file MUST be used to get the terminal
+ * number.
+ *
+ * There is no reliable way to determine the lifetime of a tty/pty.
+ * The start time of the session leader MUST be used as part of the
+ * timestamp to determine if the tty is still the same.
+ * If the start time of the session leader changed the timestamp MUST
+ * be rejected.
+ *
+ */
+
+#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
+#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <unistd.h>
* See https://www.sudo.ws/alerts/tty_tickets.html
*/
static int
-ttynr()
+proc_info(pid_t pid, int *ttynr, unsigned long long *starttime)
{
+ char path[128];
char buf[1024];
- char *p, *saveptr;
+ char *p, *saveptr, *ep;
const char *errstr;
int fd, n;
p = buf;
- if ((fd = open("/proc/self/stat", O_RDONLY)) == -1)
+ if (snprintf(path, sizeof path, "/proc/%d/stat", pid) == -1)
+ return -1;
+
+ if ((fd = open(path, O_RDONLY)) == -1)
return -1;
while ((n = read(fd, p, buf + sizeof buf - p)) != 0) {
return -1;
/* Get the 7th field, 5 fields after the last ')',
- * because the 5th field 'comm' can include spaces
- * and closing paranthesis too.
+ * (2th field) because the 5th field 'comm' can include
+ * spaces and closing paranthesis too.
* See https://www.sudo.ws/alerts/linux_tty.html
*/
if ((p = strrchr(buf, ')')) == NULL)
return -1;
- for ((p = strtok_r(p, " ", &saveptr)), n = 0; p && n < 5;
- (p = strtok_r(NULL, " ", &saveptr)), n++)
- ;
- if (p == NULL || n != 5)
- return -1;
- n = strtonum(p, INT_MIN, INT_MAX, &errstr);
- if (errstr)
- return -1;
+ n = 2;
+ for ((p = strtok_r(p, " ", &saveptr)); p;
+ (p = strtok_r(NULL, " ", &saveptr))) {
+ switch (n++) {
+ case 7:
+ *ttynr = strtonum(p, INT_MIN, INT_MAX, &errstr);
+ if (errstr)
+ return -1;
+ break;
+ case 22:
+ errno = 0;
+ *starttime = strtoull(p, &ep, 10);
+ if (p == ep ||
+ (errno == ERANGE && *starttime == ULLONG_MAX))
+ return -1;
+ break;
+ }
+ if (n == 23)
+ break;
+ }
- return n;
+ return 0;
}
#else
-#error "ttynr not implemented"
+#error "proc_info not implemented"
#endif
static const char *
tsname()
{
static char buf[128];
- int tty;
- pid_t ppid, sid;
- if ((tty = ttynr()) == -1)
+ int tty, fd;
+ unsigned long long starttime;
+ pid_t ppid, sid, leader;
+ if ((fd = open("/dev/tty", O_RDONLY)) == -1)
+ err(1, "open: /dev/tty");
+ if (ioctl(fd, TIOCGSID, &leader) == -1)
+ err(1, "ioctl: failed to get session leader");
+ close(fd);
+ if (proc_info(leader, &tty, &starttime) == -1)
errx(1, "failed to get tty number");
ppid = getppid();
if ((sid = getsid(0)) == -1)
err(1, "getsid");
- if (snprintf(buf, sizeof buf, ".%d_%d_%d", tty, ppid, sid) == -1)
+ if (snprintf(buf, sizeof buf, ".%d_%d_%llu_%d_%d",
+ tty, leader, starttime, ppid, sid) == -1)
return NULL;
return buf;
}