[Anders Kaseorg <andersk@mit.edu>]

According to getpwnam(3):

  An application that wants to determine its user's home directory
  should inspect the value of HOME (rather than the value
  getpwuid(getuid())->pw_dir) since this allows the user to modify
  their notion of "the home directory" during a login session.

This is important for systems where many users share the same UID, and for test systems that change HOME to avoid interference with the user’s real home directory.  It matches what most applications do, as well as what glibc does for glob("~", GLOB_TILDE, …) and wordexp("~", …).

There was some previous discussion of this in 2016, where although there were some questions about the use case, there seemed to be general support for the concept:

https://www.postgresql.org/message-id/flat/CAEH6cQqbdbXoUHJBbX9ixwfjFFsUC-a8hFntKcci%3DdiWgBb3fQ%40m...

Regardless of whether one thinks modifying HOME is a good idea, if we happen to find ourselves in that case, we should respect the modified HOME, so that when the user creates (say) a ~/.pgpass file, we’ll look for it at the same place the user’s editor created it.  getenv() also skips the overhead of reading /etc/passwd as an added bonus.

The way I ran into this issue myself was in a test suite that runs on GitHub Actions, which automatically sets HOME=/github/home.

Anders
=

Attachments:

v1-0001-Prefer-getenv-HOME-to-find-the-UNIX-home-director.patch (text/x-patch, 3.8K) download
From df9c435c759fffe77c9c92f70e7c095ffb6556ae Mon Sep 17 00:00:00 2001
From: Anders Kaseorg <andersk@mit.edu>
Date: Thu, 14 Oct 2021 15:20:13 -0700
Subject: [PATCH v1] Prefer getenv("HOME") to find the UNIX home directory

According to getpwnam(3):

  An application that wants to determine its user's home directory
  should inspect the value of HOME (rather than the value
  getpwuid(getuid())->pw_dir) since this allows the user to modify
  their notion of "the home directory" during a login session.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>
---
 src/bin/psql/command.c            | 20 ++++++++++++--------
 src/interfaces/libpq/fe-connect.c | 14 ++++++++++----
 src/port/path.c                   | 14 ++++++++++----
 3 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 49d4c0e3ce..cc2fe6ba0e 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -15,6 +15,7 @@
 #include <sys/stat.h>			/* for stat() */
 #include <sys/time.h>			/* for setitimer() */
 #include <fcntl.h>				/* open() flags */
+#include <stdlib.h>				/* for getenv() */
 #include <unistd.h>				/* for geteuid(), getpid(), stat() */
 #else
 #include <win32.h>
@@ -558,15 +559,18 @@ exec_command_cd(PsqlScanState scan_state, bool active_branch, const char *cmd)
 			uid_t		user_id = geteuid();
 
 			errno = 0;			/* clear errno before call */
-			pw = getpwuid(user_id);
-			if (!pw)
-			{
-				pg_log_error("could not get home directory for user ID %ld: %s",
-							 (long) user_id,
-							 errno ? strerror(errno) : _("user does not exist"));
-				exit(EXIT_FAILURE);
+			dir = getenv("HOME");
+			if (dir == NULL || dir[0] == '\0') {
+				pw = getpwuid(user_id);
+				if (!pw)
+				{
+					pg_log_error("could not get home directory for user ID %ld: %s",
+								 (long) user_id,
+								 errno ? strerror(errno) : _("user does not exist"));
+					exit(EXIT_FAILURE);
+				}
+				dir = pw->pw_dir;
 			}
-			dir = pw->pw_dir;
 #else							/* WIN32 */
 
 			/*
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index b288d346f9..ebdd815c73 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -19,6 +19,7 @@
 #include <fcntl.h>
 #include <ctype.h>
 #include <time.h>
+#include <stdlib.h>
 #include <unistd.h>
 
 #include "common/ip.h"
@@ -7242,14 +7243,19 @@ bool
 pqGetHomeDirectory(char *buf, int bufsize)
 {
 #ifndef WIN32
+	const char *home;
 	char		pwdbuf[BUFSIZ];
 	struct passwd pwdstr;
 	struct passwd *pwd = NULL;
 
-	(void) pqGetpwuid(geteuid(), &pwdstr, pwdbuf, sizeof(pwdbuf), &pwd);
-	if (pwd == NULL)
-		return false;
-	strlcpy(buf, pwd->pw_dir, bufsize);
+	home = getenv("HOME");
+	if (home == NULL || home[0] == '\0') {
+		(void) pqGetpwuid(geteuid(), &pwdstr, pwdbuf, sizeof(pwdbuf), &pwd);
+		if (pwd == NULL)
+			return false;
+		home = pwd->pw_dir;
+	}
+	strlcpy(buf, home, bufsize);
 	return true;
 #else
 	char		tmppath[MAX_PATH];
diff --git a/src/port/path.c b/src/port/path.c
index c39d4688cd..607bd16c23 100644
--- a/src/port/path.c
+++ b/src/port/path.c
@@ -32,6 +32,7 @@
 #define near
 #include <shlobj.h>
 #else
+#include <stdlib.h>
 #include <unistd.h>
 #endif
 
@@ -807,14 +808,19 @@ bool
 get_home_path(char *ret_path)
 {
 #ifndef WIN32
+	const char *home;
 	char		pwdbuf[BUFSIZ];
 	struct passwd pwdstr;
 	struct passwd *pwd = NULL;
 
-	(void) pqGetpwuid(geteuid(), &pwdstr, pwdbuf, sizeof(pwdbuf), &pwd);
-	if (pwd == NULL)
-		return false;
-	strlcpy(ret_path, pwd->pw_dir, MAXPGPATH);
+	home = getenv("HOME");
+	if (home == NULL || home[0] == '\0') {
+		(void) pqGetpwuid(geteuid(), &pwdstr, pwdbuf, sizeof(pwdbuf), &pwd);
+		if (pwd == NULL)
+			return false;
+		home = pwd->pw_dir;
+	}
+	strlcpy(ret_path, home, MAXPGPATH);
 	return true;
 #else
 	char	   *tmppath;
-- 
2.33.0