Published:
30 January 2000
Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE-----
===========================================================================
AUSCERT External Security Bulletin Redistribution
ESB-2000.020 -- FreeBSD-SA-00:02.procfs
Old procfs hole incompletely filled
31 January 2000
===========================================================================
The FreeBSD Security Team has released the following advisory concerning an
incompletely fixed vulnerability dating back to January 1997 on *BSD
systems. (The initial advisory was released as FreeBSD Security Advisory
FreeBSD-SA-97:04, redistributed as AUSCERT ESB-97.112)
This vulnerability may allow local users to gain root privileges on
affected systems.
- --------------------------BEGIN INCLUDED TEXT--------------------
- -----BEGIN PGP SIGNED MESSAGE-----
=============================================================================
FreeBSD-SA-00:01 Security Advisory
FreeBSD, Inc.
Topic: Old procfs hole incompletely filled
Category: core
Module: make
Announced: 2000-01-24
Affects: All versions before the correction date.
Corrected: 2000-01-20
FreeBSD only: NO
Patches: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-00:02/procfs.patch
I. Background
procfs provides access to other processes memory spaces. This is
intended to be used in debugging and has many safeguards built into it
to prevent abuse.
II. Problem Description
In January 1997 a fatal flaw in *BSD procfs code (leading to a local
root compromise) was discussed on various security forums. The exploit
code dealt with /proc/pid/mem interface. Since then *BSD kernels
contained a simple fix which was meant to close this hole.
Unfortunately, throughout these three years it was still possible to
abuse /proc/pid/mem in a similar, though more complicated fashion,
which could lead to local root compromise.
III. Impact
Local users can gain root access.
IV. Workaround
You can unmount /proc. In both 3.x-stable and 4.0-current this will
break truss and gcore. In 3.x-stable systems only it will reduce the
amount of information ps reports.
V. Solution
Apply the following patch
Index: sys/filedesc.h
===================================================================
RCS file: /base/FreeBSD-CVS/src/sys/sys/filedesc.h,v
retrieving revision 1.15.2.1
diff -u -r1.15.2.1 filedesc.h
--- filedesc.h 1999/08/29 16:32:22 1.15.2.1
+++ filedesc.h 2000/01/20 21:39:29
@@ -139,6 +139,7 @@
int fsetown __P((pid_t, struct sigio **));
void funsetown __P((struct sigio *));
void funsetownlst __P((struct sigiolst *));
+void setugidsafety __P((struct proc *p));
#endif
#endif
Index: kern/kern_descrip.c
===================================================================
RCS file: /base/FreeBSD-CVS/src/sys/kern/kern_descrip.c,v
retrieving revision 1.58.2.3
diff -u -r1.58.2.3 kern_descrip.c
--- kern_descrip.c 1999/11/18 08:09:08 1.58.2.3
+++ kern_descrip.c 2000/01/20 21:40:00
@@ -984,6 +984,62 @@
}
/*
+ * For setuid/setgid programs we don't want to people to use that setuidness
+ * to generate error messages which write to a file which otherwise would
+ * otherwise be off limits to the proces.
+ *
+ * This is a gross hack to plug the hole. A better solution would involve
+ * a special vop or other form of generalized access control mechanism. We
+ * go ahead and just reject all procfs file systems accesses as dangerous.
+ *
+ * Since setugidsafety calls this only for fd 0, 1 and 2, this check is
+ * sufficient. We also don't for setugidness since we know we are.
+ */
+static int
+is_unsafe(struct file *fp)
+{
+ if (fp->f_type == DTYPE_VNODE &&
+ ((struct vnode *)(fp->f_data))->v_tag == VT_PROCFS)
+ return (1);
+ return (0);
+}
+
+/*
+ * Make this setguid thing safe, if at all possible.
+ */
+void
+setugidsafety(p)
+ struct proc *p;
+{
+ struct filedesc *fdp = p->p_fd;
+ struct file **fpp;
+ char *fdfp;
+ register int i;
+
+ /* Certain daemons might not have file descriptors. */
+ if (fdp == NULL)
+ return;
+
+ fpp = fdp->fd_ofiles;
+ fdfp = fdp->fd_ofileflags;
+ for (i = 0; i <= fdp->fd_lastfile; i++, fpp++, fdfp++) {
+ if (i > 2)
+ break;
+ if (*fpp != NULL && is_unsafe(*fpp)) {
+ if (*fdfp & UF_MAPPED)
+ (void) munmapfd(p, i);
+ (void) closef(*fpp, p);
+ *fpp = NULL;
+ *fdfp = 0;
+ if (i < fdp->fd_freefile)
+ fdp->fd_freefile = i;
+ }
+ }
+ while (fdp->fd_lastfile > 0 && fdp->fd_ofiles[fdp->fd_lastfile] == NULL)
+ fdp->fd_lastfile--;
+}
+
+/*
* Close any files on exec?
*/
void
Index: kern/kern_exec.c
===================================================================
RCS file: /base/FreeBSD-CVS/src/sys/kern/kern_exec.c,v
retrieving revision 1.93.2.3
diff -u -r1.93.2.3 kern_exec.c
--- kern_exec.c 1999/08/29 16:25:58 1.93.2.3
+++ kern_exec.c 2000/01/20 21:39:29
@@ -281,6 +281,7 @@
if (attr.va_mode & VSGID)
p->p_ucred->cr_gid = attr.va_gid;
setsugid(p);
+ setugidsafety(p);
} else {
if (p->p_ucred->cr_uid == p->p_cred->p_ruid &&
p->p_ucred->cr_gid == p->p_cred->p_rgid)
VI. Credits
We are republishing a heavily edited FEAR security advisory (number 1)
entitled "*BSD procfs vulnerability". More information about FEAR can
be found at http://www.fear.pl. We would like to thank
nergal@idea.avet.com.pl for sending a preliminary version of the
advisory to us in time to correct the problem.
=============================================================================
FreeBSD, Inc.
Web Site: http://www.freebsd.org/
Confidential contacts: security-officer@freebsd.org
Security notifications: security-notifications@freebsd.org
Security public discussion: freebsd-security@freebsd.org
PGP Key: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/public_key.asc
Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
=============================================================================
- -----BEGIN PGP SIGNATURE-----
Version: 2.6.3ia
Charset: noconv
Comment: Processed by Mailcrypt 3.4, an Emacs/PGP interface
iQCVAwUBOJFWeFUuHi5z0oilAQHo2AP+N4GDREEmjxy6RUvt+G3cRe1Sx4yxr/Jd
q70D5Icp3JlcJgxGfWFqGGvt8yx9xMm6d57mFDltdvPKr0TY0n0bY39BJlRAto9n
gn8BJJvQ0WQ15ctOQKIsGwGJqHvA+p4qAHYFE3sUIZn6oMz5//C5OmaC7mFtrycY
TI64bNR+0F8=
=/F89
- -----END PGP SIGNATURE-----
- --------------------------END INCLUDED TEXT--------------------
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to use any or all of this information is
the responsibility of each user or organisation, and should be done so in
accordance with site policies and procedures.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the original authors to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
http://www.auscert.org.au/Information/advisories.html
If you believe that your system has been compromised, contact AusCERT or
your representative in FIRST (Forum of Incident Response and Security
Teams).
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for emergencies.
-----BEGIN PGP SIGNATURE-----
Version: 2.6.3i
Charset: noconv
Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key
iQCVAwUBOJ/aqih9+71yA2DNAQHYNwP/a+VD08L/jh06LmEbpmB3coYCMEDPSuHm
BPg/sVRQmIqdxc+3R9zlgcnOEoW6//M4zJkX+QvqpVNYr8aU341cF7elNky1jCiL
63OLiqgfaxdSwlmvMDerZpkH2SvovYrEwzArASUgNNgJnR7Tt/WDnZtpq4ugGIoq
erKB50T7Km4=
=8R1O
-----END PGP SIGNATURE-----