From: Nathan Bossart <nathandbossart@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: pgsql-hackers@postgresql.org
Cc: noah@leadboat.com
Subject: Re: common signal handler protection
Date: Tue, 28 Nov 2023 15:39:55 -0600
Message-ID: <20231128213955.GA474877@nathanxps13> (raw)
In-Reply-To: <20231127221625.GB140989@nathanxps13>
References: <20231121212008.GA3742740@nathanxps13>
<20231121224006.GA3747740@nathanxps13>
<20231122215944.GA3797360@nathanxps13>
<20231122225945.3kgclsgz5lqmtnan@awork3.anarazel.de>
<20231127221625.GB140989@nathanxps13>
Here is a new patch set with feedback addressed.
--
Nathan Bossart
Amazon Web Services: https://aws.amazon.comAttachments:download all (3 files, .tar.gz)v3-0001-Check-that-MyProcPid-getpid-in-all-signal-handler.patch (text/x-diff, 4.6K) download
From e4bea5353c2685457545b67396095e9b96156982 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Tue, 28 Nov 2023 14:58:20 -0600
Subject: [PATCH v3 1/3] Check that MyProcPid == getpid() in all signal
handlers.
In commit 97550c0711, we added a similar check to the SIGTERM
handler for the startup process. This commit adds this check to
all signal handlers installed with pqsignal(). This is done by
using a wrapper function that performs the check before calling the
actual handler.
The hope is that this will offer more general protection against
child processes of Postgres backends inadvertently modifying shared
memory due to inherited signal handlers. Another potential
follow-up improvement is to use this wrapper handler function to
restore errno instead of relying on each individual handler
function to do so.
This commit makes the changes in commit 97550c0711 obsolete but
leaves reverting it for a follow-up commit.
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/20231121212008.GA3742740%40nathanxps13
---
src/port/pqsignal.c | 80 +++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 78 insertions(+), 2 deletions(-)
diff --git a/src/port/pqsignal.c b/src/port/pqsignal.cindex 23e7f685c1..a7e9dc49fc 100644--- a/src/port/pqsignal.c+++ b/src/port/pqsignal.c@@ -46,23 +46,93 @@
#include "c.h"
#include <signal.h>
+#ifndef FRONTEND+#include <unistd.h>+#endif
#ifndef FRONTEND
#include "libpq/pqsignal.h"
+#include "miscadmin.h"+#endif++#ifdef PG_SIGNAL_COUNT /* Windows */+#define PG_NSIG (PG_SIGNAL_COUNT)+#elif defined(NSIG)+#define PG_NSIG (NSIG)+#else+#define PG_NSIG (64) /* XXX: wild guess */
#endif
+/* Check a couple of common signals to make sure PG_NSIG is accurate. */+StaticAssertDecl(SIGUSR2 < PG_NSIG, "SIGUSR2 >= PG_NSIG");+StaticAssertDecl(SIGHUP < PG_NSIG, "SIGHUP >= PG_NSIG");+StaticAssertDecl(SIGTERM < PG_NSIG, "SIGTERM >= PG_NSIG");+StaticAssertDecl(SIGALRM < PG_NSIG, "SIGALRM >= PG_NSIG");++static volatile pqsigfunc pqsignal_handlers[PG_NSIG];++/*+ * Except when called with SIG_IGN or SIG_DFL, pqsignal() sets up this function+ * as the handler for all signals. This wrapper handler function checks that+ * it is called within a process that the server knows about (i.e., any process+ * that has called InitProcessGlobals(), such as a client backend), and not a+ * child process forked by system(3), etc. This check ensures that such child+ * processes do not modify shared memory, which is often detrimental. If the+ * check succeeds, the function originally provided to pqsignal() is called.+ * Otherwise, the default signal handler is installed and then called.+ */+static void+wrapper_handler(SIGNAL_ARGS)+{+#ifndef FRONTEND+ Assert(MyProcPid);++ if (unlikely(MyProcPid != (int) getpid()))+ {+ pqsignal(postgres_signal_arg, SIG_DFL);+ raise(postgres_signal_arg);+ return;+ }+#endif++ (*pqsignal_handlers[postgres_signal_arg]) (postgres_signal_arg);+}+
/*
* Set up a signal handler, with SA_RESTART, for signal "signo"
*
* Returns the previous handler.
+ *+ * NB: If called within a signal handler, race conditions may lead to bogus+ * return values. You should either avoid calling this within signal handlers+ * or ignore the return value.+ *+ * XXX: Since no in-tree callers use the return value, and there is little+ * reason to do so, it would be nice if we could convert this to a void+ * function instead of providing potentially-bogus return values.+ * Unfortunately, that requires modifying the pqsignal() in legacy-pqsignal.c,+ * which in turn requires an SONAME bump, which is probably not worth it.
*/
pqsigfunc
pqsignal(int signo, pqsigfunc func)
{
+ pqsigfunc orig_func = pqsignal_handlers[signo]; /* assumed atomic */
#if !(defined(WIN32) && defined(FRONTEND))
struct sigaction act,
oact;
+#else+ pqsigfunc ret;+#endif++ Assert(signo < PG_NSIG);+ if (func != SIG_IGN && func != SIG_DFL)+ {+ pqsignal_handlers[signo] = func; /* assumed atomic */+ func = wrapper_handler;+ }++#if !(defined(WIN32) && defined(FRONTEND))
act.sa_handler = func;
sigemptyset(&act.sa_mask);
act.sa_flags = SA_RESTART;
@@ -72,9 +142,15 @@ pqsignal(int signo, pqsigfunc func)
#endif
if (sigaction(signo, &act, &oact) < 0)
return SIG_ERR;
- return oact.sa_handler;+ else if (oact.sa_handler == wrapper_handler)+ return orig_func;+ else+ return oact.sa_handler;
#else
/* Forward to Windows native signal system. */
- return signal(signo, func);+ if ((ret = signal(signo, func)) == wrapper_handler)+ return orig_func;+ else+ return ret;
#endif
}
--
2.25.1
v3-0002-Centralize-logic-for-restoring-errno-in-signal-ha.patch (text/x-diff, 10.4K) download
From a506a4ae932936222554c8be75b290eac57824d5 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Tue, 28 Nov 2023 15:18:13 -0600
Subject: [PATCH v3 2/3] Centralize logic for restoring errno in signal
handlers.
Presently, we rely on each individual signal handler to save the
initial value of errno and then restore it before returning if
needed. This is easily forgotten and, if missed, often goes
undetected for a long time.
In commit XXXXXXXXXX, we introduced a wrapper signal handler
function that checks whether MyProcPid matches getpid(). This
commit moves the aforementioned errno restoration code from the
individual signal handlers to the new wrapper handler so that we no
longer need to worry about missing it.
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/20231121212008.GA3742740%40nathanxps13
---
src/backend/postmaster/autovacuum.c | 4 ----
src/backend/postmaster/checkpointer.c | 4 ----
src/backend/postmaster/interrupt.c | 8 --------
src/backend/postmaster/pgarch.c | 4 ----
src/backend/postmaster/postmaster.c | 16 ----------------
src/backend/postmaster/startup.c | 12 ------------
src/backend/postmaster/syslogger.c | 4 ----
src/backend/replication/walsender.c | 4 ----
src/backend/storage/ipc/latch.c | 4 ----
src/backend/storage/ipc/procsignal.c | 4 ----
src/backend/tcop/postgres.c | 8 --------
src/backend/utils/misc/timeout.c | 4 ----
src/fe_utils/cancel.c | 3 ---
src/port/pqsignal.c | 6 ++++++
14 files changed, 6 insertions(+), 79 deletions(-)
diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.cindex 86a3b3d8be..ced7f72f63 100644--- a/src/backend/postmaster/autovacuum.c+++ b/src/backend/postmaster/autovacuum.c@@ -1423,12 +1423,8 @@ AutoVacWorkerFailed(void)
static void
avl_sigusr2_handler(SIGNAL_ARGS)
{
- int save_errno = errno;-
got_SIGUSR2 = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.cindex 42c807d352..6d8c1b7ce4 100644--- a/src/backend/postmaster/checkpointer.c+++ b/src/backend/postmaster/checkpointer.c@@ -834,15 +834,11 @@ IsCheckpointOnSchedule(double progress)
static void
ReqCheckpointHandler(SIGNAL_ARGS)
{
- int save_errno = errno;-
/*
* The signaling process should have set ckpt_flags nonzero, so all we
* need do is ensure that our main loop gets kicked out of any wait.
*/
SetLatch(MyLatch);
-- errno = save_errno;
}
diff --git a/src/backend/postmaster/interrupt.c b/src/backend/postmaster/interrupt.cindex 6d4bd76bf8..fa7833f673 100644--- a/src/backend/postmaster/interrupt.c+++ b/src/backend/postmaster/interrupt.c@@ -60,12 +60,8 @@ HandleMainLoopInterrupts(void)
void
SignalHandlerForConfigReload(SIGNAL_ARGS)
{
- int save_errno = errno;-
ConfigReloadPending = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
/*
@@ -108,10 +104,6 @@ SignalHandlerForCrashExit(SIGNAL_ARGS)
void
SignalHandlerForShutdownRequest(SIGNAL_ARGS)
{
- int save_errno = errno;-
ShutdownRequestPending = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
diff --git a/src/backend/postmaster/pgarch.c b/src/backend/postmaster/pgarch.cindex 46af349564..ff0958fa52 100644--- a/src/backend/postmaster/pgarch.c+++ b/src/backend/postmaster/pgarch.c@@ -283,13 +283,9 @@ PgArchWakeup(void)
static void
pgarch_waken_stop(SIGNAL_ARGS)
{
- int save_errno = errno;-
/* set flag to do a final cycle and shut down afterwards */
ready_to_stop = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
/*
diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.cindex 7a5cd06c5c..1cc8fa2c43 100644--- a/src/backend/postmaster/postmaster.c+++ b/src/backend/postmaster/postmaster.c@@ -2608,12 +2608,8 @@ InitProcessGlobals(void)
static void
handle_pm_pmsignal_signal(SIGNAL_ARGS)
{
- int save_errno = errno;-
pending_pm_pmsignal = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
/*
@@ -2622,12 +2618,8 @@ handle_pm_pmsignal_signal(SIGNAL_ARGS)
static void
handle_pm_reload_request_signal(SIGNAL_ARGS)
{
- int save_errno = errno;-
pending_pm_reload_request = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
/*
@@ -2705,8 +2697,6 @@ process_pm_reload_request(void)
static void
handle_pm_shutdown_request_signal(SIGNAL_ARGS)
{
- int save_errno = errno;-
switch (postgres_signal_arg)
{
case SIGTERM:
@@ -2723,8 +2713,6 @@ handle_pm_shutdown_request_signal(SIGNAL_ARGS)
break;
}
SetLatch(MyLatch);
-- errno = save_errno;
}
/*
@@ -2884,12 +2872,8 @@ process_pm_shutdown_request(void)
static void
handle_pm_child_exit_signal(SIGNAL_ARGS)
{
- int save_errno = errno;-
pending_pm_child_exit = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
/*
diff --git a/src/backend/postmaster/startup.c b/src/backend/postmaster/startup.cindex 0e7de26bc2..83dbed86b9 100644--- a/src/backend/postmaster/startup.c+++ b/src/backend/postmaster/startup.c@@ -96,32 +96,22 @@ static void StartupProcExit(int code, Datum arg);
static void
StartupProcTriggerHandler(SIGNAL_ARGS)
{
- int save_errno = errno;-
promote_signaled = true;
WakeupRecovery();
-- errno = save_errno;
}
/* SIGHUP: set flag to re-read config file at next convenient time */
static void
StartupProcSigHupHandler(SIGNAL_ARGS)
{
- int save_errno = errno;-
got_SIGHUP = true;
WakeupRecovery();
-- errno = save_errno;
}
/* SIGTERM: set flag to abort redo and exit */
static void
StartupProcShutdownHandler(SIGNAL_ARGS)
{
- int save_errno = errno;-
if (in_restore_command)
{
/*
@@ -140,8 +130,6 @@ StartupProcShutdownHandler(SIGNAL_ARGS)
else
shutdown_requested = true;
WakeupRecovery();
-- errno = save_errno;
}
/*
diff --git a/src/backend/postmaster/syslogger.c b/src/backend/postmaster/syslogger.cindex 96dd03d9e0..a47838d505 100644--- a/src/backend/postmaster/syslogger.c+++ b/src/backend/postmaster/syslogger.c@@ -1642,10 +1642,6 @@ RemoveLogrotateSignalFiles(void)
static void
sigUsr1Handler(SIGNAL_ARGS)
{
- int save_errno = errno;-
rotation_requested = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.cindex 3bc9c82389..a809c2202b 100644--- a/src/backend/replication/walsender.c+++ b/src/backend/replication/walsender.c@@ -3245,12 +3245,8 @@ HandleWalSndInitStopping(void)
static void
WalSndLastCycleHandler(SIGNAL_ARGS)
{
- int save_errno = errno;-
got_SIGUSR2 = true;
SetLatch(MyLatch);
-- errno = save_errno;
}
/* Set up signal handlers */
diff --git a/src/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.cindex d8a69990b3..359f648703 100644--- a/src/backend/storage/ipc/latch.c+++ b/src/backend/storage/ipc/latch.c@@ -2243,12 +2243,8 @@ GetNumRegisteredWaitEvents(WaitEventSet *set)
static void
latch_sigurg_handler(SIGNAL_ARGS)
{
- int save_errno = errno;-
if (waiting)
sendSelfPipeByte();
-- errno = save_errno;
}
/* Send one byte to the self-pipe, to wake up WaitLatch */
diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.cindex b7427906de..8e65009a89 100644--- a/src/backend/storage/ipc/procsignal.c+++ b/src/backend/storage/ipc/procsignal.c@@ -638,8 +638,6 @@ CheckProcSignal(ProcSignalReason reason)
void
procsignal_sigusr1_handler(SIGNAL_ARGS)
{
- int save_errno = errno;-
if (CheckProcSignal(PROCSIG_CATCHUP_INTERRUPT))
HandleCatchupInterrupt();
@@ -683,6 +681,4 @@ procsignal_sigusr1_handler(SIGNAL_ARGS)
HandleRecoveryConflictInterrupt(PROCSIG_RECOVERY_CONFLICT_BUFFERPIN);
SetLatch(MyLatch);
-- errno = save_errno;
}
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.cindex e415cf1f34..4bfa3fc009 100644--- a/src/backend/tcop/postgres.c+++ b/src/backend/tcop/postgres.c@@ -2970,8 +2970,6 @@ quickdie(SIGNAL_ARGS)
void
die(SIGNAL_ARGS)
{
- int save_errno = errno;-
/* Don't joggle the elbow of proc_exit */
if (!proc_exit_inprogress)
{
@@ -2993,8 +2991,6 @@ die(SIGNAL_ARGS)
*/
if (DoingCommandRead && whereToSendOutput != DestRemote)
ProcessInterrupts();
-- errno = save_errno;
}
/*
@@ -3004,8 +3000,6 @@ die(SIGNAL_ARGS)
void
StatementCancelHandler(SIGNAL_ARGS)
{
- int save_errno = errno;-
/*
* Don't joggle the elbow of proc_exit
*/
@@ -3017,8 +3011,6 @@ StatementCancelHandler(SIGNAL_ARGS)
/* If we're still here, waken anything waiting on the process latch */
SetLatch(MyLatch);
-- errno = save_errno;
}
/* signal handler for floating point exception */
diff --git a/src/backend/utils/misc/timeout.c b/src/backend/utils/misc/timeout.cindex 8ab755d363..c9790f8cdb 100644--- a/src/backend/utils/misc/timeout.c+++ b/src/backend/utils/misc/timeout.c@@ -363,8 +363,6 @@ schedule_alarm(TimestampTz now)
static void
handle_sig_alarm(SIGNAL_ARGS)
{
- int save_errno = errno;-
/*
* Bump the holdoff counter, to make sure nothing we call will process
* interrupts directly. No timeout handler should do that, but these
@@ -452,8 +450,6 @@ handle_sig_alarm(SIGNAL_ARGS)
}
RESUME_INTERRUPTS();
-- errno = save_errno;
}
diff --git a/src/fe_utils/cancel.c b/src/fe_utils/cancel.cindex 10c0cd4554..bffef24d63 100644--- a/src/fe_utils/cancel.c+++ b/src/fe_utils/cancel.c@@ -152,7 +152,6 @@ ResetCancelConn(void)
static void
handle_sigint(SIGNAL_ARGS)
{
- int save_errno = errno;
char errbuf[256];
CancelRequested = true;
@@ -173,8 +172,6 @@ handle_sigint(SIGNAL_ARGS)
write_stderr(errbuf);
}
}
-- errno = save_errno; /* just in case the write changed it */
}
/*
diff --git a/src/port/pqsignal.c b/src/port/pqsignal.cindex a7e9dc49fc..7e283e2957 100644--- a/src/port/pqsignal.c+++ b/src/port/pqsignal.c@@ -80,10 +80,14 @@ static volatile pqsigfunc pqsignal_handlers[PG_NSIG];
* processes do not modify shared memory, which is often detrimental. If the
* check succeeds, the function originally provided to pqsignal() is called.
* Otherwise, the default signal handler is installed and then called.
+ *+ * This wrapper also handles restoring the value of errno.
*/
static void
wrapper_handler(SIGNAL_ARGS)
{
+ int save_errno = errno;+
#ifndef FRONTEND
Assert(MyProcPid);
@@ -96,6 +100,8 @@ wrapper_handler(SIGNAL_ARGS)
#endif
(*pqsignal_handlers[postgres_signal_arg]) (postgres_signal_arg);
++ errno = save_errno;
}
/*
--
2.25.1
v3-0003-Revert-Avoid-calling-proc_exit-in-processes-forke.patch (text/x-diff, 3.3K) download
From ab76c25312ef3711381c4acf0456c13f6142d1bc Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Tue, 28 Nov 2023 15:25:03 -0600
Subject: [PATCH v3 3/3] Revert "Avoid calling proc_exit() in processes forked
by system()."
Thanks to commit XXXXXXXXXX, this check in the SIGTERM handler for
the startup process is now obsolete and can be removed. Instead of
leaving around the dead function write_stderr_signal_safe(), I've
opted to just remove it for now. Thanks to modern version control
software, it will be trivial to dig it up if it is ever needed in
the future.
This partially reverts commit 97550c0711.
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/20231121212008.GA3742740%40nathanxps13
---
src/backend/postmaster/startup.c | 17 +----------------
src/backend/utils/error/elog.c | 28 ----------------------------
src/include/utils/elog.h | 6 ------
3 files changed, 1 insertion(+), 50 deletions(-)
diff --git a/src/backend/postmaster/startup.c b/src/backend/postmaster/startup.cindex 83dbed86b9..f40acd20ff 100644--- a/src/backend/postmaster/startup.c+++ b/src/backend/postmaster/startup.c@@ -19,8 +19,6 @@
*/
#include "postgres.h"
-#include <unistd.h>-
#include "access/xlog.h"
#include "access/xlogrecovery.h"
#include "access/xlogutils.h"
@@ -113,20 +111,7 @@ static void
StartupProcShutdownHandler(SIGNAL_ARGS)
{
if (in_restore_command)
- {- /*- * If we are in a child process (e.g., forked by system() in- * RestoreArchivedFile()), we don't want to call any exit callbacks.- * The parent will take care of that.- */- if (MyProcPid == (int) getpid())- proc_exit(1);- else- {- write_stderr_signal_safe("StartupProcShutdownHandler() called in child process\n");- _exit(1);- }- }+ proc_exit(1);
else
shutdown_requested = true;
WakeupRecovery();
diff --git a/src/backend/utils/error/elog.c b/src/backend/utils/error/elog.cindex 6aeb855e49..ba9179da85 100644--- a/src/backend/utils/error/elog.c+++ b/src/backend/utils/error/elog.c@@ -3733,34 +3733,6 @@ write_stderr(const char *fmt,...)
}
-/*- * Write a message to STDERR using only async-signal-safe functions. This can- * be used to safely emit a message from a signal handler.- *- * TODO: It is likely possible to safely do a limited amount of string- * interpolation (e.g., %s and %d), but that is not presently supported.- */-void-write_stderr_signal_safe(const char *str)-{- int nwritten = 0;- int ntotal = strlen(str);-- while (nwritten < ntotal)- {- int rc;-- rc = write(STDERR_FILENO, str + nwritten, ntotal - nwritten);-- /* Just give up on error. There isn't much else we can do. */- if (rc == -1)- return;-- nwritten += rc;- }-}--
/*
* Adjust the level of a recovery-related message per trace_recovery_messages.
*
diff --git a/src/include/utils/elog.h b/src/include/utils/elog.hindex 0971d5ce33..b25ea65dff 100644--- a/src/include/utils/elog.h+++ b/src/include/utils/elog.h@@ -536,10 +536,4 @@ extern void write_jsonlog(ErrorData *edata);
*/
extern void write_stderr(const char *fmt,...) pg_attribute_printf(1, 2);
-/*- * Write a message to STDERR using only async-signal-safe functions. This can- * be used to safely emit a message from a signal handler.- */-extern void write_stderr_signal_safe(const char *fmt);-
#endif /* ELOG_H */
--
2.25.1
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To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, andres@anarazel.de, noah@leadboat.com
Subject: Re: common signal handler protection
In-Reply-To: <20231128213955.GA474877@nathanxps13>
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