exec.c

/*-------------------------------------------------------------------------
 *
 * exec.c
 *		Functions for finding and validating executable files
 *
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/common/exec.c
 *
 *-------------------------------------------------------------------------
 */

/*
 * On macOS, "man realpath" avers:
 *    Defining _DARWIN_C_SOURCE or _DARWIN_BETTER_REALPATH before including
 *    stdlib.h will cause the provided implementation of realpath() to use
 *    F_GETPATH from fcntl(2) to discover the path.
 * This should be harmless everywhere else.
 */
#define _DARWIN_BETTER_REALPATH

#ifndef FRONTEND
#include "postgres.h"
#else
#include "postgres_fe.h"
#endif

#include <signal.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <unistd.h>

#ifdef EXEC_BACKEND
#if defined(HAVE_SYS_PERSONALITY_H)
#include <sys/personality.h>
#elif defined(HAVE_SYS_PROCCTL_H)
#include <sys/procctl.h>
#endif
#endif

#include "common/string.h"

/* Inhibit mingw CRT's auto-globbing of command line arguments */
#if defined(WIN32) && !defined(_MSC_VER)
extern int	_CRT_glob = 0;		/* 0 turns off globbing; 1 turns it on */
#endif

/*
 * Hacky solution to allow expressing both frontend and backend error reports
 * in one macro call.  First argument of log_error is an errcode() call of
 * some sort (ignored if FRONTEND); the rest are errmsg_internal() arguments,
 * i.e. message string and any parameters for it.
 *
 * Caller must provide the gettext wrapper around the message string, if
 * appropriate, so that it gets translated in the FRONTEND case; this
 * motivates using errmsg_internal() not errmsg().  We handle appending a
 * newline, if needed, inside the macro, so that there's only one translatable
 * string per call not two.
 */
#ifndef FRONTEND
#define log_error(errcodefn, ...) \
	ereport(LOG, (errcodefn, errmsg_internal(__VA_ARGS__)))
#else
#define log_error(errcodefn, ...) \
	(fprintf(stderr, __VA_ARGS__), fputc('\n', stderr))
#endif

static int	normalize_exec_path(char *path);
static char *pg_realpath(const char *fname);

#ifdef WIN32
static BOOL GetTokenUser(HANDLE hToken, PTOKEN_USER *ppTokenUser);
#endif

/*
 * validate_exec -- validate "path" as an executable file
 *
 * returns 0 if the file is found and no error is encountered.
 *		  -1 if the regular file "path" does not exist or cannot be executed.
 *		  -2 if the file is otherwise valid but cannot be read.
 * in the failure cases, errno is set appropriately
 */
int
validate_exec(const char *path)
{
	struct stat buf;
	int			is_r;
	int			is_x;

#ifdef WIN32
	char		path_exe[MAXPGPATH + sizeof(".exe") - 1];

	/* Win32 requires a .exe suffix for stat() */
	if (strlen(path) < strlen(".exe") ||
		pg_strcasecmp(path + strlen(path) - strlen(".exe"), ".exe") != 0)
	{
		strlcpy(path_exe, path, sizeof(path_exe) - 4);
		strcat(path_exe, ".exe");
		path = path_exe;
	}
#endif

	/*
	 * Ensure that the file exists and is a regular file.
	 *
	 * XXX if you have a broken system where stat() looks at the symlink
	 * instead of the underlying file, you lose.
	 */
	if (stat(path, &buf) < 0)
		return -1;

	if (!S_ISREG(buf.st_mode))
	{
		/*
		 * POSIX offers no errno code that's simply "not a regular file".  If
		 * it's a directory we can use EISDIR.  Otherwise, it's most likely a
		 * device special file, and EPERM (Operation not permitted) isn't too
		 * horribly off base.
		 */
		errno = S_ISDIR(buf.st_mode) ? EISDIR : EPERM;
		return -1;
	}

	/*
	 * Ensure that the file is both executable and readable (required for
	 * dynamic loading).
	 */
#ifndef WIN32
	is_r = (access(path, R_OK) == 0);
	is_x = (access(path, X_OK) == 0);
	/* access() will set errno if it returns -1 */
#else
	is_r = buf.st_mode & S_IRUSR;
	is_x = buf.st_mode & S_IXUSR;
	errno = EACCES;				/* appropriate thing if we return nonzero */
#endif
	return is_x ? (is_r ? 0 : -2) : -1;
}


/*
 * find_my_exec -- find an absolute path to this program's executable
 *
 *	argv0 is the name passed on the command line
 *	retpath is the output area (must be of size MAXPGPATH)
 *	Returns 0 if OK, -1 if error.
 *
 * The reason we have to work so hard to find an absolute path is that
 * on some platforms we can't do dynamic loading unless we know the
 * executable's location.  Also, we need an absolute path not a relative
 * path because we may later change working directory.  Finally, we want
 * a true path not a symlink location, so that we can locate other files
 * that are part of our installation relative to the executable.
 */
int
find_my_exec(const char *argv0, char *retpath)
{
	char	   *path;

	/*
	 * If argv0 contains a separator, then PATH wasn't used.
	 */
	strlcpy(retpath, argv0, MAXPGPATH);
	if (first_dir_separator(retpath) != NULL)
	{
		if (validate_exec(retpath) == 0)
			return normalize_exec_path(retpath);

		log_error(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				  _("invalid binary \"%s\": %m"), retpath);
		return -1;
	}

#ifdef WIN32
	/* Win32 checks the current directory first for names without slashes */
	if (validate_exec(retpath) == 0)
		return normalize_exec_path(retpath);
#endif

	/*
	 * Since no explicit path was supplied, the user must have been relying on
	 * PATH.  We'll search the same PATH.
	 */
	if ((path = getenv("PATH")) && *path)
	{
		char	   *startp = NULL,
				   *endp = NULL;

		do
		{
			if (!startp)
				startp = path;
			else
				startp = endp + 1;

			endp = first_path_var_separator(startp);
			if (!endp)
				endp = startp + strlen(startp); /* point to end */

			strlcpy(retpath, startp, Min(endp - startp + 1, MAXPGPATH));

			join_path_components(retpath, retpath, argv0);
			canonicalize_path(retpath);

			switch (validate_exec(retpath))
			{
				case 0:			/* found ok */
					return normalize_exec_path(retpath);
				case -1:		/* wasn't even a candidate, keep looking */
					break;
				case -2:		/* found but disqualified */
					log_error(errcode(ERRCODE_WRONG_OBJECT_TYPE),
							  _("could not read binary \"%s\": %m"),
							  retpath);
					break;
			}
		} while (*endp);
	}

	log_error(errcode(ERRCODE_UNDEFINED_FILE),
			  _("could not find a \"%s\" to execute"), argv0);
	return -1;
}


/*
 * normalize_exec_path - resolve symlinks and convert to absolute path
 *
 * Given a path that refers to an executable, chase through any symlinks
 * to find the real file location; then convert that to an absolute path.
 *
 * On success, replaces the contents of "path" with the absolute path.
 * ("path" is assumed to be of size MAXPGPATH.)
 * Returns 0 if OK, -1 if error.
 */
static int
normalize_exec_path(char *path)
{
	/*
	 * We used to do a lot of work ourselves here, but now we just let
	 * realpath(3) do all the heavy lifting.
	 */
	char	   *abspath = pg_realpath(path);

	if (abspath == NULL)
	{
		log_error(errcode_for_file_access(),
				  _("could not resolve path \"%s\" to absolute form: %m"),
				  path);
		return -1;
	}
	strlcpy(path, abspath, MAXPGPATH);
	free(abspath);

#ifdef WIN32
	/* On Windows, be sure to convert '\' to '/' */
	canonicalize_path(path);
#endif

	return 0;
}


/*
 * pg_realpath() - realpath(3) with POSIX.1-2008 semantics
 *
 * This is equivalent to realpath(fname, NULL), in that it returns a
 * malloc'd buffer containing the absolute path equivalent to fname.
 * On error, returns NULL with errno set.
 *
 * On Windows, what you get is spelled per platform conventions,
 * so you probably want to apply canonicalize_path() to the result.
 *
 * For now, this is needed only here so mark it static.  If you choose to
 * move it into its own file, move the _DARWIN_BETTER_REALPATH #define too!
 */
static char *
pg_realpath(const char *fname)
{
	char	   *path;

#ifndef WIN32
	path = realpath(fname, NULL);
	if (path == NULL && errno == EINVAL)
	{
		/*
		 * Cope with old-POSIX systems that require a user-provided buffer.
		 * Assume MAXPGPATH is enough room on all such systems.
		 */
		char	   *buf = malloc(MAXPGPATH);

		if (buf == NULL)
			return NULL;		/* assume errno is set */
		path = realpath(fname, buf);
		if (path == NULL)		/* don't leak memory */
		{
			int			save_errno = errno;

			free(buf);
			errno = save_errno;
		}
	}
#else							/* WIN32 */

	/*
	 * Microsoft is resolutely non-POSIX, but _fullpath() does the same thing.
	 * The documentation claims it reports errors by setting errno, which is a
	 * bit surprising for Microsoft, but we'll believe that until it's proven
	 * wrong.  Clear errno first, though, so we can at least tell if a failure
	 * occurs and doesn't set it.
	 */
	errno = 0;
	path = _fullpath(NULL, fname, 0);
#endif

	return path;
}


/*
 * Find another program in our binary's directory,
 * then make sure it is the proper version.
 */
int
find_other_exec(const char *argv0, const char *target,
				const char *versionstr, char *retpath)
{
	char		cmd[MAXPGPATH];
	char	   *line;

	if (find_my_exec(argv0, retpath) < 0)
		return -1;

	/* Trim off program name and keep just directory */
	*last_dir_separator(retpath) = '\0';
	canonicalize_path(retpath);

	/* Now append the other program's name */
	snprintf(retpath + strlen(retpath), MAXPGPATH - strlen(retpath),
			 "/%s%s", target, EXE);

	if (validate_exec(retpath) != 0)
		return -1;

	snprintf(cmd, sizeof(cmd), "\"%s\" -V", retpath);

	if ((line = pipe_read_line(cmd)) == NULL)
		return -1;

	if (strcmp(line, versionstr) != 0)
	{
		pfree(line);
		return -2;
	}

	pfree(line);
	return 0;
}


/*
 * Execute a command in a pipe and read the first line from it. The returned
 * string is palloc'd (malloc'd in frontend code), the caller is responsible
 * for freeing.
 */
char *
pipe_read_line(char *cmd)
{
	FILE	   *pipe_cmd;
	char	   *line;

	fflush(NULL);

	errno = 0;
	if ((pipe_cmd = popen(cmd, "r")) == NULL)
	{
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  _("could not execute command \"%s\": %m"), cmd);
		return NULL;
	}

	/* Make sure popen() didn't change errno */
	errno = 0;
	line = pg_get_line(pipe_cmd, NULL);

	if (line == NULL)
	{
		if (ferror(pipe_cmd))
			log_error(errcode_for_file_access(),
					  _("could not read from command \"%s\": %m"), cmd);
		else
			log_error(errcode(ERRCODE_NO_DATA),
					  _("no data was returned by command \"%s\""), cmd);
	}

	(void) pclose_check(pipe_cmd);

	return line;
}


/*
 * pclose() plus useful error reporting
 */
int
pclose_check(FILE *stream)
{
	int			exitstatus;
	char	   *reason;

	exitstatus = pclose(stream);

	if (exitstatus == 0)
		return 0;				/* all is well */

	if (exitstatus == -1)
	{
		/* pclose() itself failed, and hopefully set errno */
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  _("%s() failed: %m"), "pclose");
	}
	else
	{
		reason = wait_result_to_str(exitstatus);
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  "%s", reason);
		pfree(reason);
	}
	return exitstatus;
}

/*
 *	set_pglocale_pgservice
 *
 *	Set application-specific locale and service directory
 *
 *	This function takes the value of argv[0] rather than a full path.
 *
 * (You may be wondering why this is in exec.c.  It requires this module's
 * services and doesn't introduce any new dependencies, so this seems as
 * good as anyplace.)
 */
void
set_pglocale_pgservice(const char *argv0, const char *app)
{
	char		path[MAXPGPATH];
	char		my_exec_path[MAXPGPATH];

	/* don't set LC_ALL in the backend */
	if (strcmp(app, PG_TEXTDOMAIN("postgres")) != 0)
	{
		setlocale(LC_ALL, "");

		/*
		 * One could make a case for reproducing here PostmasterMain()'s test
		 * for whether the process is multithreaded.  Unlike the postmaster,
		 * no frontend program calls sigprocmask() or otherwise provides for
		 * mutual exclusion between signal handlers.  While frontends using
		 * fork(), if multithreaded, are formally exposed to undefined
		 * behavior, we have not witnessed a concrete bug.  Therefore,
		 * complaining about multithreading here may be mere pedantry.
		 */
	}

	if (find_my_exec(argv0, my_exec_path) < 0)
		return;

#ifdef ENABLE_NLS
	get_locale_path(my_exec_path, path);
	bindtextdomain(app, path);
	textdomain(app);
	/* set for libpq to use, but don't override existing setting */
	setenv("PGLOCALEDIR", path, 0);
#endif

	if (getenv("PGSYSCONFDIR") == NULL)
	{
		get_etc_path(my_exec_path, path);
		/* set for libpq to use */
		setenv("PGSYSCONFDIR", path, 0);
	}
}

#ifdef EXEC_BACKEND
/*
 * For the benefit of PostgreSQL developers testing EXEC_BACKEND on Unix
 * systems (code paths normally exercised only on Windows), provide a way to
 * disable address space layout randomization, if we know how on this platform.
 * Otherwise, backends may fail to attach to shared memory at the fixed address
 * chosen by the postmaster.  (See also the macOS-specific hack in
 * sysv_shmem.c.)
 */
int
pg_disable_aslr(void)
{
#if defined(HAVE_SYS_PERSONALITY_H)
	return personality(ADDR_NO_RANDOMIZE);
#elif defined(HAVE_SYS_PROCCTL_H) && defined(PROC_ASLR_FORCE_DISABLE)
	int			data = PROC_ASLR_FORCE_DISABLE;

	return procctl(P_PID, 0, PROC_ASLR_CTL, &data);
#else
	errno = ENOSYS;
	return -1;
#endif
}
#endif

#ifdef WIN32

/*
 * AddUserToTokenDacl(HANDLE hToken)
 *
 * This function adds the current user account to the restricted
 * token used when we create a restricted process.
 *
 * This is required because of some security changes in Windows
 * that appeared in patches to XP/2K3 and in Vista/2008.
 *
 * On these machines, the Administrator account is not included in
 * the default DACL - you just get Administrators + System. For
 * regular users you get User + System. Because we strip Administrators
 * when we create the restricted token, we are left with only System
 * in the DACL which leads to access denied errors for later CreatePipe()
 * and CreateProcess() calls when running as Administrator.
 *
 * This function fixes this problem by modifying the DACL of the
 * token the process will use, and explicitly re-adding the current
 * user account.  This is still secure because the Administrator account
 * inherits its privileges from the Administrators group - it doesn't
 * have any of its own.
 */
BOOL
AddUserToTokenDacl(HANDLE hToken)
{
	int			i;
	ACL_SIZE_INFORMATION asi;
	ACCESS_ALLOWED_ACE *pace;
	DWORD		dwNewAclSize;
	DWORD		dwSize = 0;
	DWORD		dwTokenInfoLength = 0;
	PACL		pacl = NULL;
	PTOKEN_USER pTokenUser = NULL;
	TOKEN_DEFAULT_DACL tddNew;
	TOKEN_DEFAULT_DACL *ptdd = NULL;
	TOKEN_INFORMATION_CLASS tic = TokenDefaultDacl;
	BOOL		ret = FALSE;

	/* Figure out the buffer size for the DACL info */
	if (!GetTokenInformation(hToken, tic, (LPVOID) NULL, dwTokenInfoLength, &dwSize))
	{
		if (GetLastError() == ERROR_INSUFFICIENT_BUFFER)
		{
			ptdd = (TOKEN_DEFAULT_DACL *) LocalAlloc(LPTR, dwSize);
			if (ptdd == NULL)
			{
				log_error(errcode(ERRCODE_OUT_OF_MEMORY),
						  _("out of memory"));
				goto cleanup;
			}

			if (!GetTokenInformation(hToken, tic, (LPVOID) ptdd, dwSize, &dwSize))
			{
				log_error(errcode(ERRCODE_SYSTEM_ERROR),
						  "could not get token information: error code %lu",
						  GetLastError());
				goto cleanup;
			}
		}
		else
		{
			log_error(errcode(ERRCODE_SYSTEM_ERROR),
					  "could not get token information buffer size: error code %lu",
					  GetLastError());
			goto cleanup;
		}
	}

	/* Get the ACL info */
	if (!GetAclInformation(ptdd->DefaultDacl, (LPVOID) &asi,
						   (DWORD) sizeof(ACL_SIZE_INFORMATION),
						   AclSizeInformation))
	{
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  "could not get ACL information: error code %lu",
				  GetLastError());
		goto cleanup;
	}

	/* Get the current user SID */
	if (!GetTokenUser(hToken, &pTokenUser))
		goto cleanup;			/* callee printed a message */

	/* Figure out the size of the new ACL */
	dwNewAclSize = asi.AclBytesInUse + sizeof(ACCESS_ALLOWED_ACE) +
		GetLengthSid(pTokenUser->User.Sid) - sizeof(DWORD);

	/* Allocate the ACL buffer & initialize it */
	pacl = (PACL) LocalAlloc(LPTR, dwNewAclSize);
	if (pacl == NULL)
	{
		log_error(errcode(ERRCODE_OUT_OF_MEMORY),
				  _("out of memory"));
		goto cleanup;
	}

	if (!InitializeAcl(pacl, dwNewAclSize, ACL_REVISION))
	{
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  "could not initialize ACL: error code %lu", GetLastError());
		goto cleanup;
	}

	/* Loop through the existing ACEs, and build the new ACL */
	for (i = 0; i < (int) asi.AceCount; i++)
	{
		if (!GetAce(ptdd->DefaultDacl, i, (LPVOID *) &pace))
		{
			log_error(errcode(ERRCODE_SYSTEM_ERROR),
					  "could not get ACE: error code %lu", GetLastError());
			goto cleanup;
		}

		if (!AddAce(pacl, ACL_REVISION, MAXDWORD, pace, ((PACE_HEADER) pace)->AceSize))
		{
			log_error(errcode(ERRCODE_SYSTEM_ERROR),
					  "could not add ACE: error code %lu", GetLastError());
			goto cleanup;
		}
	}

	/* Add the new ACE for the current user */
	if (!AddAccessAllowedAceEx(pacl, ACL_REVISION, OBJECT_INHERIT_ACE, GENERIC_ALL, pTokenUser->User.Sid))
	{
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  "could not add access allowed ACE: error code %lu",
				  GetLastError());
		goto cleanup;
	}

	/* Set the new DACL in the token */
	tddNew.DefaultDacl = pacl;

	if (!SetTokenInformation(hToken, tic, (LPVOID) &tddNew, dwNewAclSize))
	{
		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  "could not set token information: error code %lu",
				  GetLastError());
		goto cleanup;
	}

	ret = TRUE;

cleanup:
	if (pTokenUser)
		LocalFree((HLOCAL) pTokenUser);

	if (pacl)
		LocalFree((HLOCAL) pacl);

	if (ptdd)
		LocalFree((HLOCAL) ptdd);

	return ret;
}

/*
 * GetTokenUser(HANDLE hToken, PTOKEN_USER *ppTokenUser)
 *
 * Get the users token information from a process token.
 *
 * The caller of this function is responsible for calling LocalFree() on the
 * returned TOKEN_USER memory.
 */
static BOOL
GetTokenUser(HANDLE hToken, PTOKEN_USER *ppTokenUser)
{
	DWORD		dwLength;

	*ppTokenUser = NULL;

	if (!GetTokenInformation(hToken,
							 TokenUser,
							 NULL,
							 0,
							 &dwLength))
	{
		if (GetLastError() == ERROR_INSUFFICIENT_BUFFER)
		{
			*ppTokenUser = (PTOKEN_USER) LocalAlloc(LPTR, dwLength);

			if (*ppTokenUser == NULL)
			{
				log_error(errcode(ERRCODE_OUT_OF_MEMORY),
						  _("out of memory"));
				return FALSE;
			}
		}
		else
		{
			log_error(errcode(ERRCODE_SYSTEM_ERROR),
					  "could not get token information buffer size: error code %lu",
					  GetLastError());
			return FALSE;
		}
	}

	if (!GetTokenInformation(hToken,
							 TokenUser,
							 *ppTokenUser,
							 dwLength,
							 &dwLength))
	{
		LocalFree(*ppTokenUser);
		*ppTokenUser = NULL;

		log_error(errcode(ERRCODE_SYSTEM_ERROR),
				  "could not get token information: error code %lu",
				  GetLastError());
		return FALSE;
	}

	/* Memory in *ppTokenUser is LocalFree():d by the caller */
	return TRUE;
}

#endif