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Date:      Sat, 31 Oct 2020 23:48:41 +0000 (UTC)
From:      =?UTF-8?Q?Stefan_E=c3=9fer?= <se@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r367243 - in head: lib/libc/gen sys/kern
Message-ID:  <202010312348.09VNmfWN009773@repo.freebsd.org>
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Author: se
Date: Sat Oct 31 23:48:41 2020
New Revision: 367243
URL: https://svnweb.freebsd.org/changeset/base/367243

Log:
  Make sysctl user.local a tunable that can be written at run-time
  
  This sysctl value had been provided as a read-only variable that is
  compiled into the C library based on the value of _PATH_LOCALBASE in
  paths.h.
  
  After this change, the value is compiled into the kernel as an empty
  string, which is translated to _PATH_LOCALBASE by the C library.
  
  This empty string can be overridden at boot time or by a privileged
  user at run time and will then be returned by sysctl.
  
  When set to an empty string, the value returned by sysctl reverts to
  _PATH_LOCALBASE.
  
  This update does not change the behavior on any system that does
  not modify the default value of user.localbase.
  
  I consider this change as experimental and would prefer if the run-time
  write permission was reconsidered and the sysctl variable defined with
  CLFLAG_RDTUN instead to restrict it to be set at boot time.
  
  MFC after:	1 month

Modified:
  head/lib/libc/gen/sysctl.c
  head/sys/kern/kern_mib.c

Modified: head/lib/libc/gen/sysctl.c
==============================================================================
--- head/lib/libc/gen/sysctl.c	Sat Oct 31 23:19:59 2020	(r367242)
+++ head/lib/libc/gen/sysctl.c	Sat Oct 31 23:48:41 2020	(r367243)
@@ -68,14 +68,14 @@ sysctl(const int *name, u_int namelen, void *oldp, siz
 	if (retval || name[0] != CTL_USER)
 		return (retval);
 
-	if (newp != NULL) {
-		errno = EPERM;
-		return (-1);
-	}
 	if (namelen != 2) {
 		errno = EINVAL;
 		return (-1);
 	}
+	if (newp != NULL && name[1] != USER_LOCALBASE) {
+		errno = EPERM;
+		return (-1);
+	}
 
 	switch (name[1]) {
 	case USER_CS_PATH:
@@ -88,13 +88,21 @@ sysctl(const int *name, u_int namelen, void *oldp, siz
 			memmove(oldp, _PATH_STDPATH, sizeof(_PATH_STDPATH));
 		return (0);
 	case USER_LOCALBASE:
-		if (oldp != NULL && orig_oldlen < sizeof(_PATH_LOCALBASE)) {
-			errno = ENOMEM;
-			return (-1);
+		if (oldlenp != NULL) {
+			if (oldp == NULL) {
+				if (*oldlenp == 1)
+					*oldlenp = sizeof(_PATH_LOCALBASE);
+			} else {
+				if (*oldlenp != 1)
+					return (retval);
+				if (orig_oldlen < sizeof(_PATH_LOCALBASE)) {
+					errno = ENOMEM;
+					return (-1);
+				}
+				*oldlenp = sizeof(_PATH_LOCALBASE);
+				memmove(oldp, _PATH_LOCALBASE, sizeof(_PATH_LOCALBASE));
+			}
 		}
-		*oldlenp = sizeof(_PATH_LOCALBASE);
-		if (oldp != NULL)
-			memmove(oldp, _PATH_LOCALBASE, sizeof(_PATH_LOCALBASE));
 		return (0);
 	}
 

Modified: head/sys/kern/kern_mib.c
==============================================================================
--- head/sys/kern/kern_mib.c	Sat Oct 31 23:19:59 2020	(r367242)
+++ head/sys/kern/kern_mib.c	Sat Oct 31 23:48:41 2020	(r367243)
@@ -652,8 +652,11 @@ SYSCTL_INT(_user, USER_STREAM_MAX, stream_max, CTLFLAG
     SYSCTL_NULL_INT_PTR, 0, "Min Maximum number of streams a process may have open at one time");
 SYSCTL_INT(_user, USER_TZNAME_MAX, tzname_max, CTLFLAG_RD,
     SYSCTL_NULL_INT_PTR, 0, "Min Maximum number of types supported for timezone names");
-SYSCTL_STRING(_user, USER_LOCALBASE, localbase, CTLFLAG_RD,
-    "", 0, "Prefix used to install and locate add-on packages");
+
+static char localbase[MAXPATHLEN] = "";
+
+SYSCTL_STRING(_user, USER_LOCALBASE, localbase, CTLFLAG_RWTUN,
+    localbase, sizeof(localbase), "Prefix used to install and locate add-on packages");
 
 #include <sys/vnode.h>
 SYSCTL_INT(_debug_sizeof, OID_AUTO, vnode, CTLFLAG_RD,

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