exec.c

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/*-------------------------------------------------------------------------
 *
 * exec.c
 *      Functions for finding and validating executable files
 *
 *
 * Portions Copyright (c) 1996-2025, 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;
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);
#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