dfmgr.c

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/*-------------------------------------------------------------------------
 *
 * dfmgr.c
 *    Dynamic function manager code.
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/fmgr/dfmgr.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include <sys/stat.h>
 
#ifndef WIN32
#include <dlfcn.h>
#endif                          /* !WIN32 */
 
#include "fmgr.h"
#include "lib/stringinfo.h"
#include "miscadmin.h"
#include "storage/fd.h"
#include "storage/shmem.h"
#include "utils/hsearch.h"
 
 
/* signature for PostgreSQL-specific library init function */
typedef void (*PG_init_t) (void);
 
/* hashtable entry for rendezvous variables */
typedef struct
{
    char        varName[NAMEDATALEN];   /* hash key (must be first) */
    void       *varValue;
} rendezvousHashEntry;
 
/*
 * List of dynamically loaded files (kept in malloc'd memory).
 *
 * Note: "typedef struct DynamicFileList DynamicFileList" appears in fmgr.h.
 */
struct DynamicFileList
{
    DynamicFileList *next;      /* List link */
    dev_t       device;         /* Device file is on */
#ifndef WIN32                   /* ensures we never again depend on this under
                                 * win32 */
    ino_t       inode;          /* Inode number of file */
#endif
    void       *handle;         /* a handle for pg_dl* functions */
    const Pg_magic_struct *magic;   /* Location of module's magic block */
    char        filename[FLEXIBLE_ARRAY_MEMBER];    /* Full pathname of file */
};
 
static DynamicFileList *file_list = NULL;
static DynamicFileList *file_tail = NULL;
 
/* stat() call under Win32 returns an st_ino field, but it has no meaning */
#ifndef WIN32
#define SAME_INODE(A,B) ((A).st_ino == (B).inode && (A).st_dev == (B).device)
#else
#define SAME_INODE(A,B) false
#endif
 
char       *Dynamic_library_path;
 
static void *internal_load_library(const char *libname);
pg_noreturn static void incompatible_module_error(const char *libname,
                                                  const Pg_abi_values *module_magic_data);
static char *expand_dynamic_library_name(const char *name);
static void check_restricted_library_name(const char *name);
 
/* ABI values that module needs to match to be accepted */
static const Pg_abi_values magic_data = PG_MODULE_ABI_DATA;
 
 
/*
 * Load the specified dynamic-link library file, and look for a function
 * named funcname in it.
 *
 * If the function is not found, we raise an error if signalNotFound is true,
 * else return NULL.  Note that errors in loading the library
 * will provoke ereport() regardless of signalNotFound.
 *
 * If filehandle is not NULL, then *filehandle will be set to a handle
 * identifying the library file.  The filehandle can be used with
 * lookup_external_function to lookup additional functions in the same file
 * at less cost than repeating load_external_function.
 */
void *
load_external_function(const char *filename, const char *funcname,
                       bool signalNotFound, void **filehandle)
{
    char       *fullname;
    void       *lib_handle;
    void       *retval;
 
    /* Expand the possibly-abbreviated filename to an exact path name */
    fullname = expand_dynamic_library_name(filename);
 
    /* Load the shared library, unless we already did */
    lib_handle = internal_load_library(fullname);
 
    /* Return handle if caller wants it */
    if (filehandle)
        *filehandle = lib_handle;
 
    /* Look up the function within the library. */
    retval = dlsym(lib_handle, funcname);
 
    if (retval == NULL && signalNotFound)
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_FUNCTION),
                 errmsg("could not find function \"%s\" in file \"%s\"",
                        funcname, fullname)));
 
    pfree(fullname);
    return retval;
}
 
/*
 * This function loads a shlib file without looking up any particular
 * function in it.  If the same shlib has previously been loaded,
 * we do not load it again.
 *
 * When 'restricted' is true, only libraries in the presumed-secure
 * directory $libdir/plugins may be referenced.
 */
void
load_file(const char *filename, bool restricted)
{
    char       *fullname;
 
    /* Apply security restriction if requested */
    if (restricted)
        check_restricted_library_name(filename);
 
    /* Expand the possibly-abbreviated filename to an exact path name */
    fullname = expand_dynamic_library_name(filename);
 
    /* Load the shared library, unless we already did */
    (void) internal_load_library(fullname);
 
    pfree(fullname);
}
 
/*
 * Lookup a function whose library file is already loaded.
 * Return NULL if not found.
 */
void *
lookup_external_function(void *filehandle, const char *funcname)
{
    return dlsym(filehandle, funcname);
}
 
 
/*
 * Load the specified dynamic-link library file, unless it already is
 * loaded.  Return the pg_dl* handle for the file.
 *
 * Note: libname is expected to be an exact name for the library file.
 *
 * NB: There is presently no way to unload a dynamically loaded file.  We might
 * add one someday if we can convince ourselves we have safe protocols for un-
 * hooking from hook function pointers, releasing custom GUC variables, and
 * perhaps other things that are definitely unsafe currently.
 */
static void *
internal_load_library(const char *libname)
{
    DynamicFileList *file_scanner;
    PGModuleMagicFunction magic_func;
    char       *load_error;
    struct stat stat_buf;
    PG_init_t   PG_init;
 
    /*
     * Scan the list of loaded FILES to see if the file has been loaded.
     */
    for (file_scanner = file_list;
         file_scanner != NULL &&
         strcmp(libname, file_scanner->filename) != 0;
         file_scanner = file_scanner->next)
        ;
 
    if (file_scanner == NULL)
    {
        /*
         * Check for same files - different paths (ie, symlink or link)
         */
        if (stat(libname, &stat_buf) == -1)
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not access file \"%s\": %m",
                            libname)));
 
        for (file_scanner = file_list;
             file_scanner != NULL &&
             !SAME_INODE(stat_buf, *file_scanner);
             file_scanner = file_scanner->next)
            ;
    }
 
    if (file_scanner == NULL)
    {
        /*
         * File not loaded yet.
         */
        file_scanner = (DynamicFileList *)
            malloc(offsetof(DynamicFileList, filename) + strlen(libname) + 1);
        if (file_scanner == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_OUT_OF_MEMORY),
                     errmsg("out of memory")));
 
        MemSet(file_scanner, 0, offsetof(DynamicFileList, filename));
        strcpy(file_scanner->filename, libname);
        file_scanner->device = stat_buf.st_dev;
#ifndef WIN32
        file_scanner->inode = stat_buf.st_ino;
#endif
        file_scanner->next = NULL;
 
        file_scanner->handle = dlopen(file_scanner->filename, RTLD_NOW | RTLD_GLOBAL);
        if (file_scanner->handle == NULL)
        {
            load_error = dlerror();
            free(file_scanner);
            /* errcode_for_file_access might not be appropriate here? */
            ereport(ERROR,
                    (errcode_for_file_access(),
                     errmsg("could not load library \"%s\": %s",
                            libname, load_error)));
        }
 
        /* Check the magic function to determine compatibility */
        magic_func = (PGModuleMagicFunction)
            dlsym(file_scanner->handle, PG_MAGIC_FUNCTION_NAME_STRING);
        if (magic_func)
        {
            const Pg_magic_struct *magic_data_ptr = (*magic_func) ();
 
            /* Check ABI compatibility fields */
            if (magic_data_ptr->len != sizeof(Pg_magic_struct) ||
                memcmp(&magic_data_ptr->abi_fields, &magic_data,
                       sizeof(Pg_abi_values)) != 0)
            {
                /* copy data block before unlinking library */
                Pg_magic_struct module_magic_data = *magic_data_ptr;
 
                /* try to close library */
                dlclose(file_scanner->handle);
                free(file_scanner);
 
                /* issue suitable complaint */
                incompatible_module_error(libname, &module_magic_data.abi_fields);
            }
 
            /* Remember the magic block's location for future use */
            file_scanner->magic = magic_data_ptr;
        }
        else
        {
            /* try to close library */
            dlclose(file_scanner->handle);
            free(file_scanner);
            /* complain */
            ereport(ERROR,
                    (errmsg("incompatible library \"%s\": missing magic block",
                            libname),
                     errhint("Extension libraries are required to use the PG_MODULE_MAGIC macro.")));
        }
 
        /*
         * If the library has a _PG_init() function, call it.
         */
        PG_init = (PG_init_t) dlsym(file_scanner->handle, "_PG_init");
        if (PG_init)
            (*PG_init) ();
 
        /* OK to link it into list */
        if (file_list == NULL)
            file_list = file_scanner;
        else
            file_tail->next = file_scanner;
        file_tail = file_scanner;
    }
 
    return file_scanner->handle;
}
 
/*
 * Report a suitable error for an incompatible magic block.
 */
static void
incompatible_module_error(const char *libname,
                          const Pg_abi_values *module_magic_data)
{
    StringInfoData details;
 
    /*
     * If the version doesn't match, just report that, because the rest of the
     * block might not even have the fields we expect.
     */
    if (magic_data.version != module_magic_data->version)
    {
        char        library_version[32];
 
        if (module_magic_data->version >= 1000)
            snprintf(library_version, sizeof(library_version), "%d",
                     module_magic_data->version / 100);
        else
            snprintf(library_version, sizeof(library_version), "%d.%d",
                     module_magic_data->version / 100,
                     module_magic_data->version % 100);
        ereport(ERROR,
                (errmsg("incompatible library \"%s\": version mismatch",
                        libname),
                 errdetail("Server is version %d, library is version %s.",
                           magic_data.version / 100, library_version)));
    }
 
    /*
     * Similarly, if the ABI extra field doesn't match, error out.  Other
     * fields below might also mismatch, but that isn't useful information if
     * you're using the wrong product altogether.
     */
    if (strcmp(module_magic_data->abi_extra, magic_data.abi_extra) != 0)
    {
        ereport(ERROR,
                (errmsg("incompatible library \"%s\": ABI mismatch",
                        libname),
                 errdetail("Server has ABI \"%s\", library has \"%s\".",
                           magic_data.abi_extra,
                           module_magic_data->abi_extra)));
    }
 
    /*
     * Otherwise, spell out which fields don't agree.
     *
     * XXX this code has to be adjusted any time the set of fields in a magic
     * block change!
     */
    initStringInfo(&details);
 
    if (module_magic_data->funcmaxargs != magic_data.funcmaxargs)
    {
        if (details.len)
            appendStringInfoChar(&details, '\n');
        appendStringInfo(&details,
        /* translator: %s is a variable name and %d its values */
                         _("Server has %s = %d, library has %d."),
                         "FUNC_MAX_ARGS", magic_data.funcmaxargs,
                         module_magic_data->funcmaxargs);
    }
    if (module_magic_data->indexmaxkeys != magic_data.indexmaxkeys)
    {
        if (details.len)
            appendStringInfoChar(&details, '\n');
        appendStringInfo(&details,
        /* translator: %s is a variable name and %d its values */
                         _("Server has %s = %d, library has %d."),
                         "INDEX_MAX_KEYS", magic_data.indexmaxkeys,
                         module_magic_data->indexmaxkeys);
    }
    if (module_magic_data->namedatalen != magic_data.namedatalen)
    {
        if (details.len)
            appendStringInfoChar(&details, '\n');
        appendStringInfo(&details,
        /* translator: %s is a variable name and %d its values */
                         _("Server has %s = %d, library has %d."),
                         "NAMEDATALEN", magic_data.namedatalen,
                         module_magic_data->namedatalen);
    }
    if (module_magic_data->float8byval != magic_data.float8byval)
    {
        if (details.len)
            appendStringInfoChar(&details, '\n');
        appendStringInfo(&details,
        /* translator: %s is a variable name and %d its values */
                         _("Server has %s = %s, library has %s."),
                         "FLOAT8PASSBYVAL", magic_data.float8byval ? "true" : "false",
                         module_magic_data->float8byval ? "true" : "false");
    }
 
    if (details.len == 0)
        appendStringInfoString(&details,
                               _("Magic block has unexpected length or padding difference."));
 
    ereport(ERROR,
            (errmsg("incompatible library \"%s\": magic block mismatch",
                    libname),
             errdetail_internal("%s", details.data)));
}
 
 
/*
 * Iterator functions to allow callers to scan the list of loaded modules.
 *
 * Note: currently, there is no special provision for dealing with changes
 * in the list while a scan is happening.  Current callers don't need it.
 */
DynamicFileList *
get_first_loaded_module(void)
{
    return file_list;
}
 
DynamicFileList *
get_next_loaded_module(DynamicFileList *dfptr)
{
    return dfptr->next;
}
 
/*
 * Return some details about the specified module.
 *
 * Note that module_name and module_version could be returned as NULL.
 *
 * We could dispense with this function by exposing struct DynamicFileList
 * globally, but this way seems preferable.
 */
void
get_loaded_module_details(DynamicFileList *dfptr,
                          const char **library_path,
                          const char **module_name,
                          const char **module_version)
{
    *library_path = dfptr->filename;
    *module_name = dfptr->magic->name;
    *module_version = dfptr->magic->version;
}
 
 
/*
 * If name contains a slash, check if the file exists, if so return
 * the name.  Else (no slash) try to expand using search path (see
 * find_in_path below); if that works, return the fully
 * expanded file name.  If the previous failed, append DLSUFFIX and
 * try again.  If all fails, just return the original name.
 *
 * The result will always be freshly palloc'd.
 */
static char *
expand_dynamic_library_name(const char *name)
{
    bool        have_slash;
    char       *new;
    char       *full;
 
    Assert(name);
 
    /*
     * If the value starts with "$libdir/", strip that.  This is because many
     * extensions have hardcoded '$libdir/foo' as their library name, which
     * prevents using the path.
     */
    if (strncmp(name, "$libdir/", 8) == 0)
        name += 8;
 
    have_slash = (first_dir_separator(name) != NULL);
 
    if (!have_slash)
    {
        full = find_in_path(name, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
        if (full)
            return full;
    }
    else
    {
        full = substitute_path_macro(name, "$libdir", pkglib_path);
        if (pg_file_exists(full))
            return full;
        pfree(full);
    }
 
    new = psprintf("%s%s", name, DLSUFFIX);
 
    if (!have_slash)
    {
        full = find_in_path(new, Dynamic_library_path, "dynamic_library_path", "$libdir", pkglib_path);
        pfree(new);
        if (full)
            return full;
    }
    else
    {
        full = substitute_path_macro(new, "$libdir", pkglib_path);
        pfree(new);
        if (pg_file_exists(full))
            return full;
        pfree(full);
    }
 
    /*
     * If we can't find the file, just return the string as-is. The ensuing
     * load attempt will fail and report a suitable message.
     */
    return pstrdup(name);
}
 
/*
 * Check a restricted library name.  It must begin with "$libdir/plugins/"
 * and there must not be any directory separators after that (this is
 * sufficient to prevent ".." style attacks).
 */
static void
check_restricted_library_name(const char *name)
{
    if (strncmp(name, "$libdir/plugins/", 16) != 0 ||
        first_dir_separator(name + 16) != NULL)
        ereport(ERROR,
                (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                 errmsg("access to library \"%s\" is not allowed",
                        name)));
}
 
/*
 * Substitute for any macros appearing in the given string.
 * Result is always freshly palloc'd.
 */
char *
substitute_path_macro(const char *str, const char *macro, const char *value)
{
    const char *sep_ptr;
 
    Assert(str != NULL);
    Assert(macro[0] == '$');
 
    /* Currently, we only recognize $macro at the start of the string */
    if (str[0] != '$')
        return pstrdup(str);
 
    if ((sep_ptr = first_dir_separator(str)) == NULL)
        sep_ptr = str + strlen(str);
 
    if (strlen(macro) != sep_ptr - str ||
        strncmp(str, macro, strlen(macro)) != 0)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_NAME),
                 errmsg("invalid macro name in path: %s",
                        str)));
 
    return psprintf("%s%s", value, sep_ptr);
}
 
 
/*
 * Search for a file called 'basename' in the colon-separated search
 * path given.  If the file is found, the full file name
 * is returned in freshly palloc'd memory.  If the file is not found,
 * return NULL.
 *
 * path_param is the name of the parameter that path came from, for error
 * messages.
 *
 * macro and macro_val allow substituting a macro; see
 * substitute_path_macro().
 */
char *
find_in_path(const char *basename, const char *path, const char *path_param,
             const char *macro, const char *macro_val)
{
    const char *p;
    size_t      baselen;
 
    Assert(basename != NULL);
    Assert(first_dir_separator(basename) == NULL);
    Assert(path != NULL);
    Assert(path_param != NULL);
 
    p = path;
 
    /*
     * If the path variable is empty, don't do a path search.
     */
    if (strlen(p) == 0)
        return NULL;
 
    baselen = strlen(basename);
 
    for (;;)
    {
        size_t      len;
        char       *piece;
        char       *mangled;
        char       *full;
 
        piece = first_path_var_separator(p);
        if (piece == p)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_NAME),
                     errmsg("zero-length component in parameter \"%s\"", path_param)));
 
        if (piece == NULL)
            len = strlen(p);
        else
            len = piece - p;
 
        piece = palloc(len + 1);
        strlcpy(piece, p, len + 1);
 
        mangled = substitute_path_macro(piece, macro, macro_val);
        pfree(piece);
 
        canonicalize_path(mangled);
 
        /* only absolute paths */
        if (!is_absolute_path(mangled))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_NAME),
                     errmsg("component in parameter \"%s\" is not an absolute path", path_param)));
 
        full = palloc(strlen(mangled) + 1 + baselen + 1);
        sprintf(full, "%s/%s", mangled, basename);
        pfree(mangled);
 
        elog(DEBUG3, "%s: trying \"%s\"", __func__, full);
 
        if (pg_file_exists(full))
            return full;
 
        pfree(full);
 
        if (p[len] == '\0')
            break;
        else
            p += len + 1;
    }
 
    return NULL;
}
 
 
/*
 * Find (or create) a rendezvous variable that one dynamically
 * loaded library can use to meet up with another.
 *
 * On the first call of this function for a particular varName,
 * a "rendezvous variable" is created with the given name.
 * The value of the variable is a void pointer (initially set to NULL).
 * Subsequent calls with the same varName just return the address of
 * the existing variable.  Once created, a rendezvous variable lasts
 * for the life of the process.
 *
 * Dynamically loaded libraries can use rendezvous variables
 * to find each other and share information: they just need to agree
 * on the variable name and the data it will point to.
 */
void      **
find_rendezvous_variable(const char *varName)
{
    static HTAB *rendezvousHash = NULL;
 
    rendezvousHashEntry *hentry;
    bool        found;
 
    /* Create a hashtable if we haven't already done so in this process */
    if (rendezvousHash == NULL)
    {
        HASHCTL     ctl;
 
        ctl.keysize = NAMEDATALEN;
        ctl.entrysize = sizeof(rendezvousHashEntry);
        rendezvousHash = hash_create("Rendezvous variable hash",
                                     16,
                                     &ctl,
                                     HASH_ELEM | HASH_STRINGS);
    }
 
    /* Find or create the hashtable entry for this varName */
    hentry = (rendezvousHashEntry *) hash_search(rendezvousHash,
                                                 varName,
                                                 HASH_ENTER,
                                                 &found);
 
    /* Initialize to NULL if first time */
    if (!found)
        hentry->varValue = NULL;
 
    return &hentry->varValue;
}
 
/*
 * Estimate the amount of space needed to serialize the list of libraries
 * we have loaded.
 */
Size
EstimateLibraryStateSpace(void)
{
    DynamicFileList *file_scanner;
    Size        size = 1;
 
    for (file_scanner = file_list;
         file_scanner != NULL;
         file_scanner = file_scanner->next)
        size = add_size(size, strlen(file_scanner->filename) + 1);
 
    return size;
}
 
/*
 * Serialize the list of libraries we have loaded to a chunk of memory.
 */
void
SerializeLibraryState(Size maxsize, char *start_address)
{
    DynamicFileList *file_scanner;
 
    for (file_scanner = file_list;
         file_scanner != NULL;
         file_scanner = file_scanner->next)
    {
        Size        len;
 
        len = strlcpy(start_address, file_scanner->filename, maxsize) + 1;
        Assert(len < maxsize);
        maxsize -= len;
        start_address += len;
    }
    start_address[0] = '\0';
}
 
/*
 * Load every library the serializing backend had loaded.
 */
void
RestoreLibraryState(char *start_address)
{
    while (*start_address != '\0')
    {
        internal_load_library(start_address);
        start_address += strlen(start_address) + 1;
    }
}