From ed0cdf0e05134d1084b01bf8a77e9e1dc5081f91 Mon Sep 17 00:00:00 2001 From: Tom Lane Date: Sun, 9 Sep 2018 12:23:23 -0400 Subject: [PATCH] Install a check for mis-linking of src/port and src/common functions. On ELF-based platforms (and maybe others?) it's possible for a shared library, when dynamically loaded into the backend, to call the backend versions of src/port and src/common functions rather than the frontend versions that are actually linked into the shlib. This is definitely not what we want, because the frontend versions often behave slightly differently. Up to now it's been "slight" enough that nobody noticed; but with the addition of SCRAM support functions in src/common, we're observing crashes due to the difference between palloc and malloc memory allocation rules, as reported in bug #15367 from Jeremy Evans. The purpose of this patch is to create a direct test for this type of mis-linking, so that we know whether any given platform requires extra measures to prevent using the wrong functions. If the test fails, it will lead to connection failures in the contrib/postgres_fdw regression test. At the moment, *BSD platforms using ELF format are known to have the problem and can be expected to fail; but we need to know whether anything else does, and we need a reliable ongoing check for future platforms. Actually fixing the problem will be the subject of later commit(s). Discussion: https://postgr.es/m/153626613985.23143.4743626885618266803@wrigleys.postgresql.org --- src/backend/bootstrap/bootstrap.c | 8 +++++++ src/common/Makefile | 3 ++- src/common/link-canary.c | 36 +++++++++++++++++++++++++++++++ src/include/common/link-canary.h | 17 +++++++++++++++ src/interfaces/libpq/.gitignore | 1 + src/interfaces/libpq/Makefile | 6 +++--- src/interfaces/libpq/fe-connect.c | 14 ++++++++++++ src/tools/msvc/Mkvcbuild.pm | 3 ++- 8 files changed, 83 insertions(+), 5 deletions(-) create mode 100644 src/common/link-canary.c create mode 100644 src/include/common/link-canary.h diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c index cdd71a9bc3..578af2e66d 100644 --- a/src/backend/bootstrap/bootstrap.c +++ b/src/backend/bootstrap/bootstrap.c @@ -24,6 +24,7 @@ #include "catalog/index.h" #include "catalog/pg_collation.h" #include "catalog/pg_type.h" +#include "common/link-canary.h" #include "libpq/pqsignal.h" #include "miscadmin.h" #include "nodes/makefuncs.h" @@ -502,6 +503,13 @@ BootstrapModeMain(void) Assert(!IsUnderPostmaster); Assert(IsBootstrapProcessingMode()); + /* + * To ensure that src/common/link-canary.c is linked into the backend, we + * must call it from somewhere. Here is as good as anywhere. + */ + if (pg_link_canary_is_frontend()) + elog(ERROR, "backend is incorrectly linked to frontend functions"); + /* * Do backend-like initialization for bootstrap mode */ diff --git a/src/common/Makefile b/src/common/Makefile index 1fc2c66225..687174788e 100644 --- a/src/common/Makefile +++ b/src/common/Makefile @@ -41,7 +41,8 @@ override CPPFLAGS := -DFRONTEND $(CPPFLAGS) LIBS += $(PTHREAD_LIBS) OBJS_COMMON = base64.o config_info.o controldata_utils.o exec.o file_perm.o \ - ip.o keywords.o md5.o pg_lzcompress.o pgfnames.o psprintf.o relpath.o \ + ip.o keywords.o link-canary.o md5.o pg_lzcompress.o \ + pgfnames.o psprintf.o relpath.o \ rmtree.o saslprep.o scram-common.o string.o unicode_norm.o \ username.o wait_error.o diff --git a/src/common/link-canary.c b/src/common/link-canary.c new file mode 100644 index 0000000000..5b4e562220 --- /dev/null +++ b/src/common/link-canary.c @@ -0,0 +1,36 @@ +/*------------------------------------------------------------------------- + * link-canary.c + * Detect whether src/common functions came from frontend or backend. + * + * Copyright (c) 2018, PostgreSQL Global Development Group + * + * IDENTIFICATION + * src/common/link-canary.c + * + *------------------------------------------------------------------------- + */ +#include "c.h" + +#include "common/link-canary.h" + +/* + * This function just reports whether this file was compiled for frontend + * or backend environment. We need this because in some systems, mainly + * ELF-based platforms, it is possible for a shlib (such as libpq) loaded + * into the backend to call a backend function named XYZ in preference to + * the shlib's own function XYZ. That's bad if the two functions don't + * act identically. This exact situation comes up for many functions in + * src/common and src/port, where the same function names exist in both + * libpq and the backend but they don't act quite identically. To verify + * that appropriate measures have been taken to prevent incorrect symbol + * resolution, libpq should test that this function returns true. + */ +bool +pg_link_canary_is_frontend(void) +{ +#ifdef FRONTEND + return true; +#else + return false; +#endif +} diff --git a/src/include/common/link-canary.h b/src/include/common/link-canary.h new file mode 100644 index 0000000000..917faae9ef --- /dev/null +++ b/src/include/common/link-canary.h @@ -0,0 +1,17 @@ +/*------------------------------------------------------------------------- + * + * link-canary.h + * Detect whether src/common functions came from frontend or backend. + * + * Copyright (c) 2018, PostgreSQL Global Development Group + * + * src/include/common/link-canary.h + * + *------------------------------------------------------------------------- + */ +#ifndef LINK_CANARY_H +#define LINK_CANARY_H + +extern bool pg_link_canary_is_frontend(void); + +#endif /* LINK_CANARY_H */ diff --git a/src/interfaces/libpq/.gitignore b/src/interfaces/libpq/.gitignore index 5c232ae2d1..ce1576e262 100644 --- a/src/interfaces/libpq/.gitignore +++ b/src/interfaces/libpq/.gitignore @@ -25,6 +25,7 @@ /ip.c /md5.c /base64.c +/link-canary.c /scram-common.c /sha2.c /sha2_openssl.c diff --git a/src/interfaces/libpq/Makefile b/src/interfaces/libpq/Makefile index abe0a50e98..ec0122a901 100644 --- a/src/interfaces/libpq/Makefile +++ b/src/interfaces/libpq/Makefile @@ -49,7 +49,7 @@ endif # src/backend/utils/mb OBJS += encnames.o wchar.o # src/common -OBJS += base64.o ip.o md5.o scram-common.o saslprep.o unicode_norm.o +OBJS += base64.o ip.o link-canary.o md5.o scram-common.o saslprep.o unicode_norm.o ifeq ($(with_openssl),yes) OBJS += fe-secure-openssl.o fe-secure-common.o sha2_openssl.o @@ -106,7 +106,7 @@ backend_src = $(top_srcdir)/src/backend chklocale.c crypt.c erand48.c getaddrinfo.c getpeereid.c inet_aton.c inet_net_ntop.c noblock.c open.c system.c pgsleep.c pg_strong_random.c pgstrcasecmp.c pqsignal.c snprintf.c strerror.c strlcpy.c strnlen.c thread.c win32error.c win32setlocale.c: % : $(top_srcdir)/src/port/% rm -f $@ && $(LN_S) $< . -ip.c md5.c base64.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c: % : $(top_srcdir)/src/common/% +ip.c md5.c base64.c link-canary.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c: % : $(top_srcdir)/src/common/% rm -f $@ && $(LN_S) $< . encnames.c wchar.c: % : $(backend_src)/utils/mb/% @@ -156,7 +156,7 @@ clean distclean: clean-lib rm -f pg_config_paths.h # Remove files we (may have) symlinked in from src/port and other places rm -f chklocale.c crypt.c erand48.c getaddrinfo.c getpeereid.c inet_aton.c inet_net_ntop.c noblock.c open.c system.c pgsleep.c pg_strong_random.c pgstrcasecmp.c pqsignal.c snprintf.c strerror.c strlcpy.c strnlen.c thread.c win32error.c win32setlocale.c - rm -f ip.c md5.c base64.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c + rm -f ip.c md5.c base64.c link-canary.c scram-common.c sha2.c sha2_openssl.c saslprep.c unicode_norm.c rm -f encnames.c wchar.c maintainer-clean: distclean maintainer-clean-lib diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c index db5aacd0e9..42cdb971a3 100644 --- a/src/interfaces/libpq/fe-connect.c +++ b/src/interfaces/libpq/fe-connect.c @@ -71,6 +71,7 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options, #endif #include "common/ip.h" +#include "common/link-canary.h" #include "common/scram-common.h" #include "mb/pg_wchar.h" #include "port/pg_bswap.h" @@ -1748,6 +1749,19 @@ connectDBStart(PGconn *conn) if (!conn->options_valid) goto connect_errReturn; + /* + * Check for bad linking to backend-internal versions of src/common + * functions (see comments in link-canary.c for the reason we need this). + * Nobody but developers should see this message, so we don't bother + * translating it. + */ + if (!pg_link_canary_is_frontend()) + { + printfPQExpBuffer(&conn->errorMessage, + "libpq is incorrectly linked to backend functions\n"); + goto connect_errReturn; + } + /* Ensure our buffers are empty */ conn->inStart = conn->inCursor = conn->inEnd = 0; conn->outCount = 0; diff --git a/src/tools/msvc/Mkvcbuild.pm b/src/tools/msvc/Mkvcbuild.pm index 14d2a3c4cf..9ce03ce684 100644 --- a/src/tools/msvc/Mkvcbuild.pm +++ b/src/tools/msvc/Mkvcbuild.pm @@ -116,7 +116,8 @@ sub mkvcbuild our @pgcommonallfiles = qw( base64.c config_info.c controldata_utils.c exec.c file_perm.c ip.c - keywords.c md5.c pg_lzcompress.c pgfnames.c psprintf.c relpath.c rmtree.c + keywords.c link-canary.c md5.c + pg_lzcompress.c pgfnames.c psprintf.c relpath.c rmtree.c saslprep.c scram-common.c string.c unicode_norm.c username.c wait_error.c); -- 2.40.0