Date: Wed, 11 Aug 2004 14:17:06 +0200 From: Marcin Koziej <creep@desk.pl> To: FreeBSD-gnats-submit@FreeBSD.org Subject: kern/70298: manipulation of ufs system flags in jail(8) is permitted for super user Message-ID: <20040811121745.2666136E6F@niobe.desk.pl> Resent-Message-ID: <200408111220.i7BCKU2d093668@freefall.freebsd.org>
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>Number: 70298
>Category: kern
>Synopsis: manipulation of ufs system flags in jail(8) is permitted for super user
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Wed Aug 11 12:20:30 GMT 2004
>Closed-Date:
>Last-Modified:
>Originator: Marcin Koziej
>Release: FreeBSD 5.2.1-RELEASE-p9 i386
>Organization:
DESK.pl
>Environment:
System: FreeBSD mistress 5.2.1-RELEASE-p9 FreeBSD 5.2.1-RELEASE-p9 #0: Fri Jul 30 02:52:09 CEST 2004 creep@mistress:/usr/src/sys/i386/compile/MONSUN i386
>Description:
Uid 0 user can modify system flags in jail, which shouldn't
happen according to sys/ufs/ufs/ufs_vnops.c:498
/*
* Unprivileged processes and privileged processes in
* jail() are not permitted to unset system flags, or
* modify flags if any system flags are set.
* Privileged non-jail processes may not modify system flags
* if securelevel > 0 and any existing system flags are set.
*/
but after that there is:
if (!suser_cred(cred, PRISON_ROOT)) {
(code for unprivileged)
} else {
(code for superuser)
}
PRISON_ROOT flag makes uid 0 in jail(8) privileged and should be
replaced with 0.
>How-To-Repeat:
root:~:# uname -a; id; ps awux |grep $$
FreeBSD mistress 5.2.1-RELEASE-p9 FreeBSD 5.2.1-RELEASE-p9 #0: Fri Jul 30 02:52:09 CEST 2004 creep@mistress:/usr/src/sys/i386/compile/MONSUN i386
uid=0(root) gid=0(wheel) groups=0(wheel), 2(kmem), 3(sys), 4(tty), 5(operator)
root 633 0,0 1,3 2244 1608 p7 Ss 13:23 0:00,05 /usr/local/bin/zsh -i
root 637 0,0 0,2 424 212 p7 DL+ 13:23 0:00,01 grep 633
root:~:# touch test; ls -lo test
-rw-r--r-- 1 root wheel - 0 11 Sie 13:24 test
root:~:# chflags schg test; ls -lo test
-rw-r--r-- 1 root wheel schg 0 11 Sie 13:24 test
root:~:# jail / test 127.0.0.1 $SHELL
root:/:# ps awux |grep $$
root 642 0,0 1,3 2244 1608 p7 SJ 13:24 0:00,06 /usr/local/bin/zsh
root 644 0,0 0,6 1460 764 p7 DL+J 13:24 0:00,01 grep 642
root:/:# cd
root:~:# ls -lo test
-rw-r--r-- 1 root wheel schg 0 11 Sie 13:24 test
root:~:# chflags noschg test; ls -lo test
-rw-r--r-- 1 root wheel - 0 11 Sie 13:24 test
root:~:# exit
>Fix:
To fix it PRISON_ROOT flag needs to be replaced with 0.
----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----
--- sys/ufs/ufs/ufs_vnops.c.orig Tue Sep 23 15:52:43 2003
+++ sys/ufs/ufs/ufs_vnops.c Tue Sep 23 15:52:48 2003
@@ -502,7 +502,7 @@
* Privileged non-jail processes may not modify system flags
* if securelevel > 0 and any existing system flags are set.
*/
- if (!suser_cred(cred, PRISON_ROOT)) {
+ if (!suser_cred(cred, 0)) {
if (ip->i_flags
& (SF_NOUNLINK | SF_IMMUTABLE | SF_APPEND)) {
error = securelevel_gt(cred, 0);
----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----
Also, an explicit description of what PRISON_ROOT flag do would
prevent this kind of errors in the future.
----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----
--- sys/kern/kern_prot.c.orig Wed Aug 11 13:56:29 2004
+++ sys/kern/kern_prot.c Wed Aug 11 13:58:54 2004
@@ -1227,7 +1227,8 @@
/*
* Test whether the specified credentials imply "super-user" privilege.
* Return 0 or EPERM. The flag argument is currently used only to
- * specify jail interaction.
+ * specify jail interaction. PRISON_ROOT bit set in flag argument provides
+ * uid 0 in jail with "super-user" privilege.
*/
int
suser_cred(struct ucred *cred, int flag)
----8<----8<----8<----8<----8<----8<----8<----8<----8<----8<----
suser_cred with PRISON_ROOT is called in various places in the kernel,
maybe they should be revised.
Big thanks to all FreeBSD developers for providing a great OS.
--
m.
>Release-Note:
>Audit-Trail:
>Unformatted:
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