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diff --git a/src/utmp.c b/src/utmp.c
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+/*
+ * SPDX-License-Identifier: ISC
+ *
+ * Copyright (c) 2011-2018 Todd C. Miller <Todd.Miller@sudo.ws>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/*
+ * This is an open source non-commercial project. Dear PVS-Studio, please check it.
+ * PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
+ */
+
+#include <config.h>
+
+#include <sys/time.h>
+#include <sys/wait.h>
+#include <string.h>
+#include <unistd.h>
+#include <time.h>
+#if defined(HAVE_UTMPS_H)
+# include <utmps.h>
+#elif defined(HAVE_UTMPX_H)
+# include <utmpx.h>
+#else
+# include <utmp.h>
+#endif /* HAVE_UTMPS_H */
+#ifdef HAVE_GETTTYENT
+# include <ttyent.h>
+#endif
+#include <fcntl.h>
+#include <signal.h>
+
+#include "sudo.h"
+#include "sudo_exec.h"
+
+/*
+ * GCC 8 warns about strncpy() where the size field is the size of the buffer.
+ * However, strings in utmp may not be NUL terminated so this usage is correct.
+ */
+#if __GNUC_PREREQ__(8, 0)
+# pragma GCC diagnostic ignored "-Wstringop-truncation"
+#endif
+
+/*
+ * Simplify handling of different utmp types.
+ */
+#if defined(HAVE_GETUTSID)
+# define sudo_getutline(u) GETUTSLINE(u)
+# define sudo_pututline(u) PUTUTSLINE(u)
+# define sudo_setutent() SETUTSENT()
+# define sudo_endutent() ENDUTSENT()
+#elif defined(HAVE_GETUTXID)
+# define sudo_getutline(u) getutxline(u)
+# define sudo_pututline(u) pututxline(u)
+# define sudo_setutent() setutxent()
+# define sudo_endutent() endutxent()
+#elif defined(HAVE_GETUTID)
+# define sudo_getutline(u) getutline(u)
+# define sudo_pututline(u) pututline(u)
+# define sudo_setutent() setutent()
+# define sudo_endutent() endutent()
+#endif
+
+#if defined(HAVE_GETUTSID)
+typedef struct utmps sudo_utmp_t;
+#elif defined(HAVE_GETUTXID)
+typedef struct utmpx sudo_utmp_t;
+#else
+typedef struct utmp sudo_utmp_t;
+/* Older systems have ut_name, not ut_user */
+# if !defined(HAVE_STRUCT_UTMP_UT_USER) && !defined(ut_user)
+# define ut_user ut_name
+# endif
+#endif
+
+/* HP-UX has __e_termination and __e_exit, others may lack the __ */
+#if defined(HAVE_STRUCT_UTMP_UT_EXIT_E_TERMINATION)
+# undef __e_termination
+# define __e_termination e_termination
+# undef __e_exit
+# define __e_exit e_exit
+#endif
+
+#if defined(HAVE_STRUCT_UTMP_UT_ID)
+/*
+ * Create ut_id from the new ut_line and the old ut_id.
+ */
+static void
+utmp_setid(sudo_utmp_t *old, sudo_utmp_t *new)
+{
+ const char *line = new->ut_line;
+ size_t idlen;
+ debug_decl(utmp_setid, SUDO_DEBUG_UTMP);
+
+ /* Skip over "tty" in the id if old entry did too. */
+ if (old != NULL) {
+ /* cppcheck-suppress uninitdata */
+ if (strncmp(line, "tty", 3) == 0) {
+ idlen = MIN(sizeof(old->ut_id), 3);
+ if (strncmp(old->ut_id, "tty", idlen) != 0)
+ line += 3;
+ }
+ }
+
+ /* Store as much as will fit, skipping parts of the beginning as needed. */
+ /* cppcheck-suppress uninitdata */
+ idlen = strlen(line);
+ if (idlen > sizeof(new->ut_id)) {
+ line += idlen - sizeof(new->ut_id);
+ idlen = sizeof(new->ut_id);
+ }
+ strncpy(new->ut_id, line, idlen);
+
+ debug_return;
+}
+#endif /* HAVE_STRUCT_UTMP_UT_ID */
+
+/*
+ * Store time in utmp structure.
+ */
+static void
+utmp_settime(sudo_utmp_t *ut)
+{
+ struct timeval tv;
+ debug_decl(utmp_settime, SUDO_DEBUG_UTMP);
+
+ if (gettimeofday(&tv, NULL) == 0) {
+#if defined(HAVE_STRUCT_UTMP_UT_TV)
+ ut->ut_tv.tv_sec = tv.tv_sec;
+ ut->ut_tv.tv_usec = tv.tv_usec;
+#else
+ ut->ut_time = tv.tv_sec;
+#endif
+ }
+
+ debug_return;
+}
+
+/*
+ * Fill in a utmp entry, using an old entry as a template if there is one.
+ */
+static void
+utmp_fill(const char *line, const char *user, sudo_utmp_t *ut_old,
+ sudo_utmp_t *ut_new)
+{
+ debug_decl(utmp_file, SUDO_DEBUG_UTMP);
+
+ if (ut_old == NULL) {
+ memset(ut_new, 0, sizeof(*ut_new));
+ if (user == NULL) {
+ strncpy(ut_new->ut_user, user_details.username,
+ sizeof(ut_new->ut_user));
+ }
+ } else if (ut_old != ut_new) {
+ memcpy(ut_new, ut_old, sizeof(*ut_new));
+ }
+ if (user != NULL)
+ strncpy(ut_new->ut_user, user, sizeof(ut_new->ut_user));
+ strncpy(ut_new->ut_line, line, sizeof(ut_new->ut_line));
+#if defined(HAVE_STRUCT_UTMP_UT_ID)
+ utmp_setid(ut_old, ut_new);
+#endif
+#if defined(HAVE_STRUCT_UTMP_UT_PID)
+ ut_new->ut_pid = getpid();
+#endif
+ utmp_settime(ut_new);
+#if defined(HAVE_STRUCT_UTMP_UT_TYPE)
+ ut_new->ut_type = USER_PROCESS;
+#endif
+ debug_return;
+}
+
+/*
+ * There are two basic utmp file types:
+ *
+ * POSIX: sequential access with new entries appended to the end.
+ * Manipulated via {get,put}[sx]?utent()
+ *
+ * Legacy: sparse file indexed by ttyslot() * sizeof(struct utmp)
+ */
+#if defined(HAVE_GETUTSID) || defined(HAVE_GETUTXID) || defined(HAVE_GETUTID)
+bool
+utmp_login(const char *from_line, const char *to_line, int ttyfd,
+ const char *user)
+{
+ sudo_utmp_t utbuf, *ut_old = NULL;
+ bool ret = false;
+ debug_decl(utmp_login, SUDO_DEBUG_UTMP);
+
+ /* Strip off /dev/ prefix from line as needed. */
+ if (strncmp(to_line, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
+ to_line += sizeof(_PATH_DEV) - 1;
+ sudo_setutent();
+ if (from_line != NULL) {
+ if (strncmp(from_line, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
+ from_line += sizeof(_PATH_DEV) - 1;
+
+ /* Lookup old line. */
+ memset(&utbuf, 0, sizeof(utbuf));
+ strncpy(utbuf.ut_line, from_line, sizeof(utbuf.ut_line));
+ ut_old = sudo_getutline(&utbuf);
+ }
+ utmp_fill(to_line, user, ut_old, &utbuf);
+ if (sudo_pututline(&utbuf) != NULL)
+ ret = true;
+ sudo_endutent();
+
+ debug_return_bool(ret);
+}
+
+bool
+utmp_logout(const char *line, int status)
+{
+ bool ret = false;
+ sudo_utmp_t *ut, utbuf;
+ debug_decl(utmp_logout, SUDO_DEBUG_UTMP);
+
+ /* Strip off /dev/ prefix from line as needed. */
+ if (strncmp(line, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
+ line += sizeof(_PATH_DEV) - 1;
+
+ memset(&utbuf, 0, sizeof(utbuf));
+ strncpy(utbuf.ut_line, line, sizeof(utbuf.ut_line));
+ if ((ut = sudo_getutline(&utbuf)) != NULL) {
+ memset(ut->ut_user, 0, sizeof(ut->ut_user));
+# if defined(HAVE_STRUCT_UTMP_UT_TYPE)
+ ut->ut_type = DEAD_PROCESS;
+# endif
+# if defined(HAVE_STRUCT_UTMP_UT_EXIT)
+ ut->ut_exit.__e_termination = WIFSIGNALED(status) ? WTERMSIG(status) : 0;
+ ut->ut_exit.__e_exit = WIFEXITED(status) ? WEXITSTATUS(status) : 0;
+# endif
+ utmp_settime(ut);
+ if (sudo_pututline(ut) != NULL)
+ ret = true;
+ }
+ debug_return_bool(ret);
+}
+
+#else /* !HAVE_GETUTSID && !HAVE_GETUTXID && !HAVE_GETUTID */
+
+/*
+ * Find the slot for the specified line (tty name and file descriptor).
+ * Returns a slot suitable for seeking into utmp on success or <= 0 on error.
+ * If getttyent() is available we can use that to compute the slot.
+ */
+# ifdef HAVE_GETTTYENT
+static int
+utmp_slot(const char *line, int ttyfd)
+{
+ int slot = 1;
+ struct ttyent *tty;
+ debug_decl(utmp_slot, SUDO_DEBUG_UTMP);
+
+ setttyent();
+ while ((tty = getttyent()) != NULL) {
+ if (strcmp(line, tty->ty_name) == 0)
+ break;
+ slot++;
+ }
+ endttyent();
+ debug_return_int(tty ? slot : 0);
+}
+# elif defined(HAVE_TTYSLOT)
+static int
+utmp_slot(const char *line, int ttyfd)
+{
+ int sfd, slot;
+ debug_decl(utmp_slot, SUDO_DEBUG_UTMP);
+
+ /*
+ * Temporarily point stdin to the tty since ttyslot()
+ * doesn't take an argument.
+ */
+ if ((sfd = dup(STDIN_FILENO)) == -1)
+ sudo_fatal("%s", U_("unable to save stdin"));
+ if (dup2(ttyfd, STDIN_FILENO) == -1)
+ sudo_fatal("%s", U_("unable to dup2 stdin"));
+ slot = ttyslot();
+ if (dup2(sfd, STDIN_FILENO) == -1)
+ sudo_fatal("%s", U_("unable to restore stdin"));
+ close(sfd);
+
+ debug_return_int(slot);
+}
+# else /* !HAVE_TTYSLOT */
+static int
+utmp_slot(const char *line, int ttyfd)
+{
+ return -1;
+}
+# endif /* HAVE_GETTTYENT */
+
+bool
+utmp_login(const char *from_line, const char *to_line, int ttyfd,
+ const char *user)
+{
+ sudo_utmp_t utbuf, *ut_old = NULL;
+ bool ret = false;
+ int slot;
+ FILE *fp;
+ debug_decl(utmp_login, SUDO_DEBUG_UTMP);
+
+ /* Strip off /dev/ prefix from line as needed. */
+ if (strncmp(to_line, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
+ to_line += sizeof(_PATH_DEV) - 1;
+
+ /* Find slot for new entry. */
+ slot = utmp_slot(to_line, ttyfd);
+ if (slot <= 0)
+ goto done;
+
+ if ((fp = fopen(_PATH_UTMP, "r+")) == NULL)
+ goto done;
+
+ if (from_line != NULL) {
+ if (strncmp(from_line, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
+ from_line += sizeof(_PATH_DEV) - 1;
+
+ /* Lookup old line. */
+ while (fread(&utbuf, sizeof(utbuf), 1, fp) == 1) {
+# ifdef HAVE_STRUCT_UTMP_UT_ID
+ if (utbuf.ut_type != LOGIN_PROCESS && utbuf.ut_type != USER_PROCESS)
+ continue;
+# endif
+ if (utbuf.ut_user[0] &&
+ !strncmp(utbuf.ut_line, from_line, sizeof(utbuf.ut_line))) {
+ ut_old = &utbuf;
+ break;
+ }
+ }
+ }
+ utmp_fill(to_line, user, ut_old, &utbuf);
+ if (fseeko(fp, slot * (off_t)sizeof(utbuf), SEEK_SET) == 0) {
+ if (fwrite(&utbuf, sizeof(utbuf), 1, fp) == 1)
+ ret = true;
+ }
+ fclose(fp);
+
+done:
+ debug_return_bool(ret);
+}
+
+bool
+utmp_logout(const char *line, int status)
+{
+ sudo_utmp_t utbuf;
+ bool ret = false;
+ FILE *fp;
+ debug_decl(utmp_logout, SUDO_DEBUG_UTMP);
+
+ if ((fp = fopen(_PATH_UTMP, "r+")) == NULL)
+ debug_return_int(ret);
+
+ /* Strip off /dev/ prefix from line as needed. */
+ if (strncmp(line, _PATH_DEV, sizeof(_PATH_DEV) - 1) == 0)
+ line += sizeof(_PATH_DEV) - 1;
+
+ while (fread(&utbuf, sizeof(utbuf), 1, fp) == 1) {
+ if (!strncmp(utbuf.ut_line, line, sizeof(utbuf.ut_line))) {
+ memset(utbuf.ut_user, 0, sizeof(utbuf.ut_user));
+# if defined(HAVE_STRUCT_UTMP_UT_TYPE)
+ utbuf.ut_type = DEAD_PROCESS;
+# endif
+ utmp_settime(&utbuf);
+ /* Back up and overwrite record. */
+ if (fseeko(fp, (off_t)0 - (off_t)sizeof(utbuf), SEEK_CUR) == 0) {
+ if (fwrite(&utbuf, sizeof(utbuf), 1, fp) == 1)
+ ret = true;
+ }
+ break;
+ }
+ }
+ fclose(fp);
+
+ debug_return_bool(ret);
+}
+#endif /* HAVE_GETUTSID || HAVE_GETUTXID || HAVE_GETUTID */
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