v2-0006-libpq-oauth-Never-link-against-libpq-s-encoding-f.patch

From 41132991bb4df9099eefa2b419da7462c0a1b369 Mon Sep 17 00:00:00 2001
From: Jacob Champion <jacob.champion@enterprisedb.com>
Date: Wed, 3 Dec 2025 09:53:44 -0800
Subject: [PATCH v2 6/7] libpq-oauth: Never link against libpq's encoding
 functions

Now that libpq-oauth doesn't have to match the major version of libpq,
some things in pg_wchar.h are technically unsafe for us to use. (See
b6c7cfac8 for a fuller discussion.) This is unlikely to be a problem --
we only care about UTF-8 in the context of OAuth right now -- but if
anyone did introduce a way to hit it, it'd be extremely difficult to
debug or reproduce, and it'd be a potential security vulnerability to
boot.

Define USE_PRIVATE_ENCODING_FUNCS so that anyone who tries to add a
dependency on the exported APIs will simply fail to link the shared
module.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Discussion: https://postgr.es/m/CAOYmi%2BmrGg%2Bn_X2MOLgeWcj3v_M00gR8uz_D7mM8z%3DdX1JYVbg%40mail.gmail.com
---
 src/interfaces/libpq-oauth/meson.build | 10 +++++++++-
 src/interfaces/libpq-oauth/Makefile    | 11 +++++++++--
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/src/interfaces/libpq-oauth/meson.build b/src/interfaces/libpq-oauth/meson.build
index 11199100b28..b755990490d 100644
--- a/src/interfaces/libpq-oauth/meson.build
+++ b/src/interfaces/libpq-oauth/meson.build
@@ -12,7 +12,15 @@ libpq_oauth_sources = files(
 libpq_oauth_so_sources = files(
   'oauth-utils.c',
 )
-libpq_oauth_so_c_args = ['-DUSE_DYNAMIC_OAUTH']
+libpq_oauth_so_c_args = [
+  '-DUSE_DYNAMIC_OAUTH',
+
+  # A bit of forward-looking paranoia: don't allow anyone to accidentally depend
+  # on the encoding IDs coming from libpq. They're not guaranteed to match the
+  # IDs in use by our version of pgcommon, now that we allow the major version
+  # of libpq to differ from the major version of libpq-oauth.
+  '-DUSE_PRIVATE_ENCODING_FUNCS',
+]
 
 export_file = custom_target('libpq-oauth.exports',
   kwargs: gen_export_kwargs,
diff --git a/src/interfaces/libpq-oauth/Makefile b/src/interfaces/libpq-oauth/Makefile
index 0febb393feb..4572fe780d0 100644
--- a/src/interfaces/libpq-oauth/Makefile
+++ b/src/interfaces/libpq-oauth/Makefile
@@ -24,6 +24,14 @@ override shlib := lib$(NAME)$(DLSUFFIX)
 override CPPFLAGS := -I$(libpq_srcdir) -I$(top_builddir)/src/port $(CPPFLAGS) $(LIBCURL_CPPFLAGS)
 override CFLAGS += $(PTHREAD_CFLAGS)
 
+override CPPFLAGS_SHLIB := -DUSE_DYNAMIC_OAUTH
+
+# A bit of forward-looking paranoia: don't allow libpq-oauth.so to accidentally
+# depend on the encoding IDs coming from libpq. They're not guaranteed to match
+# the IDs in use by our version of pgcommon, now that we allow the major version
+# of libpq to differ from the major version of libpq-oauth.
+override CPPFLAGS_SHLIB += -DUSE_PRIVATE_ENCODING_FUNCS
+
 OBJS = \
 	$(WIN32RES)
 
@@ -34,8 +42,7 @@ OBJS_SHLIB = \
 	oauth-curl_shlib.o \
 	oauth-utils.o \
 
-oauth-utils.o: override CPPFLAGS += -DUSE_DYNAMIC_OAUTH
-oauth-curl_shlib.o: override CPPFLAGS_SHLIB += -DUSE_DYNAMIC_OAUTH
+oauth-utils.o: override CPPFLAGS += $(CPPFLAGS_SHLIB)
 
 # Add shlib-/stlib-specific objects.
 $(shlib): override OBJS += $(OBJS_SHLIB)
-- 
2.34.1