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oauth: Disallow synchronous DNS in libcurl

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There is concern that a blocking DNS lookup in libpq could stall a
backend process (say, via FDW). Since there's currently no strong
evidence that synchronous DNS is a popular option, disallow it entirely
rather than warning at configure time. We can revisit if anyone
complains.

Per query from Andres Freund.

Author: Jacob Champion <jacob.champion@enterprisedb.com>
Discussion: https://postgr.es/m/p4bd7mn6dxr2zdak74abocyltpfdxif4pxqzixqpxpetjwt34h%40qc6jgfmoddvq
This commit is contained in:
Thomas Munro 2025-03-19 16:56:19 +13:00
parent 434dbf6907
commit d7e40845f9
3 changed files with 16 additions and 26 deletions
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10
config/programs.m4
View File

@ -316,7 +316,7 @@ AC_DEFUN([PGAC_CHECK_LIBCURL],
[Define to 1 if curl_global_init() is guaranteed to be thread-safe.]) [Define to 1 if curl_global_init() is guaranteed to be thread-safe.])
fi fi
# Warn if a thread-friendly DNS resolver isn't built. # Fail if a thread-friendly DNS resolver isn't built.
AC_CACHE_CHECK([for curl support for asynchronous DNS], [pgac_cv__libcurl_async_dns], AC_CACHE_CHECK([for curl support for asynchronous DNS], [pgac_cv__libcurl_async_dns],
[AC_RUN_IFELSE([AC_LANG_PROGRAM([ [AC_RUN_IFELSE([AC_LANG_PROGRAM([
#include <curl/curl.h> #include <curl/curl.h>
@ -332,10 +332,10 @@ AC_DEFUN([PGAC_CHECK_LIBCURL],
[pgac_cv__libcurl_async_dns=yes], [pgac_cv__libcurl_async_dns=yes],
[pgac_cv__libcurl_async_dns=no], [pgac_cv__libcurl_async_dns=no],
[pgac_cv__libcurl_async_dns=unknown])]) [pgac_cv__libcurl_async_dns=unknown])])
if test x"$pgac_cv__libcurl_async_dns" != xyes ; then if test x"$pgac_cv__libcurl_async_dns" = xno ; then
AC_MSG_WARN([ AC_MSG_ERROR([
*** The installed version of libcurl does not support asynchronous DNS *** The installed version of libcurl does not support asynchronous DNS
*** lookups. Connection timeouts will not be honored during DNS resolution, *** lookups. Rebuild libcurl with the AsynchDNS feature enabled in order
*** which may lead to hangs in client programs.]) *** to use it with libpq.])
fi fi
])# PGAC_CHECK_LIBCURL ])# PGAC_CHECK_LIBCURL

14
configure vendored
View File

@ -12493,7 +12493,7 @@ $as_echo "#define HAVE_THREADSAFE_CURL_GLOBAL_INIT 1" >>confdefs.h
fi fi
# Warn if a thread-friendly DNS resolver isn't built. # Fail if a thread-friendly DNS resolver isn't built.
{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for curl support for asynchronous DNS" >&5 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for curl support for asynchronous DNS" >&5
$as_echo_n "checking for curl support for asynchronous DNS... " >&6; } $as_echo_n "checking for curl support for asynchronous DNS... " >&6; }
if ${pgac_cv__libcurl_async_dns+:} false; then : if ${pgac_cv__libcurl_async_dns+:} false; then :
@ -12535,15 +12535,11 @@ fi
fi fi
{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__libcurl_async_dns" >&5 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $pgac_cv__libcurl_async_dns" >&5
$as_echo "$pgac_cv__libcurl_async_dns" >&6; } $as_echo "$pgac_cv__libcurl_async_dns" >&6; }
if test x"$pgac_cv__libcurl_async_dns" != xyes ; then if test x"$pgac_cv__libcurl_async_dns" = xno ; then
{ $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: as_fn_error $? "
*** The installed version of libcurl does not support asynchronous DNS *** The installed version of libcurl does not support asynchronous DNS
*** lookups. Connection timeouts will not be honored during DNS resolution, *** lookups. Rebuild libcurl with the AsynchDNS feature enabled in order
*** which may lead to hangs in client programs." >&5 *** to use it with libpq." "$LINENO" 5
$as_echo "$as_me: WARNING:
*** The installed version of libcurl does not support asynchronous DNS
*** lookups. Connection timeouts will not be honored during DNS resolution,
*** which may lead to hangs in client programs." >&2;}
fi fi
fi fi

18
meson.build
View File

@ -909,9 +909,7 @@ if not libcurlopt.disabled()
cdata.set('HAVE_THREADSAFE_CURL_GLOBAL_INIT', 1) cdata.set('HAVE_THREADSAFE_CURL_GLOBAL_INIT', 1)
endif endif
# Warn if a thread-friendly DNS resolver isn't built. # Fail if a thread-friendly DNS resolver isn't built.
libcurl_async_dns = false
if not meson.is_cross_build() if not meson.is_cross_build()
r = cc.run(''' r = cc.run('''
#include <curl/curl.h> #include <curl/curl.h>
@ -931,16 +929,12 @@ if not libcurlopt.disabled()
) )
assert(r.compiled()) assert(r.compiled())
if r.returncode() == 0 if r.returncode() != 0
libcurl_async_dns = true error('''
endif
endif
if not libcurl_async_dns
warning('''
*** The installed version of libcurl does not support asynchronous DNS *** The installed version of libcurl does not support asynchronous DNS
*** lookups. Connection timeouts will not be honored during DNS resolution, *** lookups. Rebuild libcurl with the AsynchDNS feature enabled in order
*** which may lead to hangs in client programs.''') *** to use it with libpq.''')
endif
endif endif
endif endif