From 1412e6051a0b76522e0111dc01b9abf0f4607893 Mon Sep 17 00:00:00 2001
From: Jelte Fennema <github-tech@jeltef.nl>
Date: Tue, 7 Sep 2021 11:22:46 +0200
Subject: [PATCH 1/2] Add editorconfig file

This way Github knows how to display tabs correctly. Without it
indentation is a mess and it's very hard to read the code.
---
 .editorconfig | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 .editorconfig

diff --git a/.editorconfig b/.editorconfig
new file mode 100644
index 0000000..2d1a065
--- /dev/null
+++ b/.editorconfig
@@ -0,0 +1,14 @@
+
+# top-most EditorConfig file
+root = true
+
+# rules for all files
+# we use tabs with indent size 4
+[*]
+indent_style = spaces
+indent_size = 4
+tab_width = 8
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+trim_trailing_whitespace = true

From a9daad89401340defe9bddd3c26fff6d772a7c2c Mon Sep 17 00:00:00 2001
From: Jelte Fennema <github-tech@jeltef.nl>
Date: Tue, 7 Sep 2021 11:36:55 +0200
Subject: [PATCH 2/2] Guard against race conditions

Accessing proc without having a lock is unsafe, because the entry that
it points to might be reused.
---
 prioritize.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/prioritize.c b/prioritize.c
index 872cef2..38ac2b8 100644
--- a/prioritize.c
+++ b/prioritize.c
@@ -74,14 +74,20 @@ set_backend_priority(PG_FUNCTION_ARGS)
     else if (!superuser()) {
 	/*
          * Since the user is not superuser, check for matching roles. Trust
-         * that BackendPidGetProc will return NULL if the pid isn't valid,
-         * even though the check for whether it's a backend process is below.
-         * The IsBackendPid check can't be relied on as definitive even if it
-         * was first. The process might end between successive checks
+         * that BackendPidGetProcWithLock will return NULL if the pid isn't
+         * valid, even though the check for whether it's a backend process is
+         * below. The IsBackendPid check can't be relied on as definitive even
+         * if it was first. The process might end between successive checks
          * regardless of their order. There's no way to acquire a lock on an
          * arbitrary process to prevent that.
+         *
+         * We do take the ProcArrayLock manually instead of using
+         * BackendPidGetProc, because we need to be sure that the contents of
+         * proc don't change from under us while we're using them.
          */
-        proc = BackendPidGetProc(pid);
+        LWLockAcquire(ProcArrayLock, LW_SHARED);
+
+        proc = BackendPidGetProcWithLock(pid);
 
 	if (proc == NULL) {
 	    /*
@@ -94,9 +100,12 @@ set_backend_priority(PG_FUNCTION_ARGS)
 	}
 
 	else if (proc->roleId != GetUserId())
+            LWLockRelease(ProcArrayLock);
 	    ereport(ERROR,
                 (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
                  (errmsg("must be superuser to nice arbitrary backends"))));
+        LWLockRelease(ProcArrayLock);
+
 
 	/* Otherwise, the backend PID is valid and our user is allowed
 	 * to set its priority.