Protect yourself against future threats.
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===========================================================================
AUSCERT External Security Bulletin Redistribution
ESB-97.112 -- FreeBSD Security Advisory FreeBSD-SA-97:04
Security Compromise via procfs
27 August 1997
===========================================================================
The FreeBSD Security Team has released the following advisory concerning
a vulnerability in procfs kernel code. This vulnerability may allow any
user with a local account to gain root access.
The following security bulletin is provided as a service to AUSCERT's
members. As AUSCERT did not write this document, AUSCERT has had no
control over its content. As such, 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.
Contact information for FreeBSD, Inc. is included in the Security Bulletin
below. 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 4477
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.
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=============================================================================
FreeBSD-SA-97:04 Security Advisory
FreeBSD, Inc.
Topic: security compromise via procfs
Category: core
Module: procfs
Announced: 1997-08-19
Affects: FreeBSD 2.1.*, FreeBSD 2.2.*,
FreeBSD-stable and FreeBSD-current
before 1997/08/12 suffer from this problem.
Corrected: FreeBSD-current as of 1997/08/12
FreeBSD-stable as of 1997/08/12
FreeBSD 2.1-stable as of 1997/08/25
FreeBSD only: no (also other BSD systems may be affected)
Patches: ftp://freebsd.org/pub/CERT/patches/SA-97:04/
=============================================================================
I. Background
Procfs provides a filesystem interface to processes on a system.
Among others it is used by ps(1) and gdb(1).
II. Problem Description
A problem exists in the procfs kernel code that allows processes
to write memory of other processes where it should have been prohibited.
III. Impact
The hole can be used by any user on the system to gain root privileges.
IV. Workaround
A workaround is to disable the mounting of procfs. To achieve this,
edit the file /etc/fstab and put a '#' in front of the line
proc /proc procfs rw 0 0
Note that when you do that, some utilities may either not work anymore
or have a limited functionality.
V. Solution
Apply one of the following patches in /usr/src/sys/miscfs/procfs,
rebuild your kernel, install it and reboot your system.
For 2.1 and 2.2 systems:
Index: procfs_regs.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_regs.c,v
retrieving revision 1.3
retrieving revision 1.3.4.1
diff -u -r1.3 -r1.3.4.1
--- procfs_regs.c 1996/01/24 18:41:25 1.3
+++ procfs_regs.c 1997/08/12 04:45:25 1.3.4.1
@@ -36,7 +36,7 @@
*
* @(#)procfs_regs.c 8.3 (Berkeley) 1/27/94
*
- * $Id: procfs_regs.c,v 1.3 1996/01/24 18:41:25 peter Exp $
+ * $Id: procfs_regs.c,v 1.3.4.1 1997/08/12 04:45:25 sef Exp $
*/
#include <sys/param.h>
@@ -62,6 +62,8 @@
char *kv;
int kl;
+ if (!CHECKIO(curp, p))
+ return EPERM;
kl = sizeof(r);
kv = (char *) &r;
Index: procfs.h
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs.h,v
retrieving revision 1.12
retrieving revision 1.12.2.1
diff -u -r1.12 -r1.12.2.1
--- procfs.h 1996/07/02 13:38:07 1.12
+++ procfs.h 1997/08/12 04:45:20 1.12.2.1
@@ -36,7 +36,7 @@
*
* @(#)procfs.h 8.6 (Berkeley) 2/3/94
*
- * $Id: procfs.h,v 1.12 1996/07/02 13:38:07 dyson Exp $
+ * $Id: procfs.h,v 1.12.2.1 1997/08/12 04:45:20 sef Exp $
*/
/*
@@ -83,6 +83,18 @@
(bcmp((s), (cnp)->cn_nameptr, (len)) == 0))
#define KMEM_GROUP 2
+
+/*
+ * Check to see whether access to target process is allowed
+ * Evaluates to 1 if access is allowed.
+ */
+#define CHECKIO(p1, p2)
+ ((((p1)->p_cred->pc_ucred->cr_uid == (p2)->p_cred->p_ruid) &&
+ ((p1)->p_cred->p_ruid == (p2)->p_cred->p_ruid) &&
+ ((p1)->p_cred->p_svuid == (p2)->p_cred->p_ruid) &&
+ ((p2)->p_flag & P_SUGID) == 0) ||
+ (suser((p1)->p_cred->pc_ucred, &(p1)->p_acflag) == 0))
+
/*
* Format of a directory entry in /proc, ...
* This must map onto struct dirent (see <dirent.h>)
Index: procfs_mem.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_mem.c,v
retrieving revision 1.20
retrieving revision 1.20.2.1
diff -u -r1.20 -r1.20.2.1
--- procfs_mem.c 1996/10/24 02:47:05 1.20
+++ procfs_mem.c 1997/08/12 04:45:23 1.20.2.1
@@ -37,7 +37,7 @@
*
* @(#)procfs_mem.c 8.4 (Berkeley) 1/21/94
*
- * $Id: procfs_mem.c,v 1.20 1996/10/24 02:47:05 dyson Exp $
+ * $Id: procfs_mem.c,v 1.20.2.1 1997/08/12 04:45:23 sef Exp $
*/
/*
@@ -300,6 +300,23 @@
if (uio->uio_resid == 0)
return (0);
+ /*
+ * XXX
+ * We need to check for KMEM_GROUP because ps is sgid kmem;
+ * not allowing it here causes ps to not work properly. Arguably,
+ * this is a bug with what ps does. We only need to do this
+ * for Pmem nodes, and only if it's reading. This is still not
+ * good, as it may still be possible to grab illicit data if
+ * a process somehow gets to be KMEM_GROUP. Note that this also
+ * means that KMEM_GROUP can't change without editing procfs.h!
+ * All in all, quite yucky.
+ */
+
+ if (!CHECKIO(curp, p) &&
+ !(curp->p_cred->pc_ucred->cr_gid == KMEM_GROUP &&
+ uio->uio_rw == UIO_READ))
+ return EPERM;
+
error = procfs_rwmem(p, uio);
return (error);
Index: procfs_vnops.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_vnops.c,v
retrieving revision 1.24
retrieving revision 1.24.2.1
diff -u -r1.24 -r1.24.2.1
--- procfs_vnops.c 1996/09/03 14:23:10 1.24
+++ procfs_vnops.c 1997/08/12 04:45:27 1.24.2.1
@@ -36,7 +36,7 @@
*
* @(#)procfs_vnops.c 8.6 (Berkeley) 2/7/94
*
- * $Id: procfs_vnops.c,v 1.24 1996/09/03 14:23:10 bde Exp $
+ * $Id: procfs_vnops.c,v 1.24.2.1 1997/08/12 04:45:27 sef Exp $
*/
/*
@@ -120,16 +120,21 @@
struct vop_open_args *ap;
{
struct pfsnode *pfs = VTOPFS(ap->a_vp);
+ struct proc *p1 = ap->a_p, *p2 = PFIND(pfs->pfs_pid);
+
+ if (p2 == NULL)
+ return ENOENT;
switch (pfs->pfs_type) {
case Pmem:
- if (PFIND(pfs->pfs_pid) == 0)
- return (ENOENT); /* was ESRCH, jsp */
-
if (((pfs->pfs_flags & FWRITE) && (ap->a_mode & O_EXCL)) ||
((pfs->pfs_flags & O_EXCL) && (ap->a_mode & FWRITE)))
return (EBUSY);
+ if (!CHECKIO(p1, p2) &&
+ (p1->p_cred->pc_ucred->cr_gid != KMEM_GROUP))
+ return EPERM;
+
if (ap->a_mode & FWRITE)
pfs->pfs_flags = ap->a_mode & (FWRITE|O_EXCL);
@@ -176,7 +181,6 @@
procfs_ioctl(ap)
struct vop_ioctl_args *ap;
{
-
return (ENOTTY);
}
Index: procfs_fpregs.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_fpregs.c,v
retrieving revision 1.3
retrieving revision 1.3.4.1
diff -u -r1.3 -r1.3.4.1
--- procfs_fpregs.c 1996/01/24 18:40:56 1.3
+++ procfs_fpregs.c 1997/08/12 05:24:20 1.3.4.1
@@ -36,7 +36,7 @@
*
* @(#)procfs_fpregs.c 8.1 (Berkeley) 1/27/94
*
- * $Id: procfs_fpregs.c,v 1.3 1996/01/24 18:40:56 peter Exp $
+ * $Id: procfs_fpregs.c,v 1.3.4.1 1997/08/12 05:24:20 sef Exp $
*/
#include <sys/param.h>
@@ -62,6 +62,8 @@
char *kv;
int kl;
+ if (!CHECKIO(curp, p))
+ return EPERM;
kl = sizeof(r);
kv = (char *) &r;
For FreeBSd-current systems:
Index: procfs_regs.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_regs.c,v
retrieving revision 1.7
retrieving revision 1.8
diff -u -r1.7 -r1.8
--- procfs_regs.c 1997/08/02 14:32:16 1.7
+++ procfs_regs.c 1997/08/12 04:34:29 1.8
@@ -37,7 +37,7 @@
* @(#)procfs_regs.c 8.4 (Berkeley) 6/15/94
*
* From:
- * $Id: procfs_regs.c,v 1.7 1997/08/02 14:32:16 bde Exp $
+ * $Id: procfs_regs.c,v 1.8 1997/08/12 04:34:29 sef Exp $
*/
#include <sys/param.h>
@@ -60,6 +60,8 @@
char *kv;
int kl;
+ if (!CHECKIO(curp, p))
+ return EPERM;
kl = sizeof(r);
kv = (char *) &r;
Index: procfs.h
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs.h,v
retrieving revision 1.15
retrieving revision 1.16
diff -u -r1.15 -r1.16
--- procfs.h 1997/02/22 09:40:26 1.15
+++ procfs.h 1997/08/12 04:34:27 1.16
@@ -37,7 +37,7 @@
* @(#)procfs.h 8.9 (Berkeley) 5/14/95
*
* From:
- * $Id: procfs.h,v 1.15 1997/02/22 09:40:26 peter Exp $
+ * $Id: procfs.h,v 1.16 1997/08/12 04:34:27 sef Exp $
*/
/*
@@ -85,6 +85,18 @@
(bcmp((s), (cnp)->cn_nameptr, (len)) == 0))
#define KMEM_GROUP 2
+
+/*
+ * Check to see whether access to target process is allowed
+ * Evaluates to 1 if access is allowed.
+ */
+#define CHECKIO(p1, p2)
+ ((((p1)->p_cred->pc_ucred->cr_uid == (p2)->p_cred->p_ruid) &&
+ ((p1)->p_cred->p_ruid == (p2)->p_cred->p_ruid) &&
+ ((p1)->p_cred->p_svuid == (p2)->p_cred->p_ruid) &&
+ ((p2)->p_flag & P_SUGID) == 0) ||
+ (suser((p1)->p_cred->pc_ucred, &(p1)->p_acflag) == 0))
+
/*
* Format of a directory entry in /proc, ...
* This must map onto struct dirent (see <dirent.h>)
Index: procfs_mem.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_mem.c,v
retrieving revision 1.26
retrieving revision 1.27
diff -u -r1.26 -r1.27
--- procfs_mem.c 1997/08/02 14:32:14 1.26
+++ procfs_mem.c 1997/08/12 04:34:28 1.27
@@ -37,7 +37,7 @@
*
* @(#)procfs_mem.c 8.5 (Berkeley) 6/15/94
*
- * $Id: procfs_mem.c,v 1.26 1997/08/02 14:32:14 bde Exp $
+ * $Id: procfs_mem.c,v 1.27 1997/08/12 04:34:28 sef Exp $
*/
/*
@@ -276,6 +276,23 @@
if (uio->uio_resid == 0)
return (0);
+
+ /*
+ * XXX
+ * We need to check for KMEM_GROUP because ps is sgid kmem;
+ * not allowing it here causes ps to not work properly. Arguably,
+ * this is a bug with what ps does. We only need to do this
+ * for Pmem nodes, and only if it's reading. This is still not
+ * good, as it may still be possible to grab illicit data if
+ * a process somehow gets to be KMEM_GROUP. Note that this also
+ * means that KMEM_GROUP can't change without editing procfs.h!
+ * All in all, quite yucky.
+ */
+
+ if (!CHECKIO(curp, p) &&
+ !(curp->p_cred->pc_ucred->cr_gid == KMEM_GROUP &&
+ uio->uio_rw == UIO_READ))
+ return EPERM;
return (procfs_rwmem(p, uio));
}
Index: procfs_vnops.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_vnops.c,v
retrieving revision 1.30
retrieving revision 1.31
diff -u -r1.30 -r1.31
--- procfs_vnops.c 1997/08/02 14:32:20 1.30
+++ procfs_vnops.c 1997/08/12 04:34:30 1.31
@@ -36,7 +36,7 @@
*
* @(#)procfs_vnops.c 8.18 (Berkeley) 5/21/95
*
- * $Id: procfs_vnops.c,v 1.30 1997/08/02 14:32:20 bde Exp $
+ * $Id: procfs_vnops.c,v 1.31 1997/08/12 04:34:30 sef Exp $
*/
/*
@@ -127,16 +127,21 @@
} */ *ap;
{
struct pfsnode *pfs = VTOPFS(ap->a_vp);
+ struct proc *p1 = ap->a_p, *p2 = PFIND(pfs->pfs_pid);
+
+ if (p2 == NULL)
+ return ENOENT;
switch (pfs->pfs_type) {
case Pmem:
- if (PFIND(pfs->pfs_pid) == 0)
- return (ENOENT); /* was ESRCH, jsp */
-
if ((pfs->pfs_flags & FWRITE) && (ap->a_mode & O_EXCL) ||
(pfs->pfs_flags & O_EXCL) && (ap->a_mode & FWRITE))
return (EBUSY);
+ if (!CHECKIO(p1, p2) &&
+ (p1->p_cred->pc_ucred->cr_gid != KMEM_GROUP))
+ return EPERM;
+
if (ap->a_mode & FWRITE)
pfs->pfs_flags = ap->a_mode & (FWRITE|O_EXCL);
@@ -194,7 +199,6 @@
struct proc *a_p;
} */ *ap;
{
-
return (ENOTTY);
}
Index: procfs_fpregs.c
===================================================================
RCS file: /home/cvsup/freebsd/CVS/src/sys/miscfs/procfs/procfs_fpregs.c,v
retrieving revision 1.7
retrieving revision 1.8
diff -u -r1.7 -r1.8
--- procfs_fpregs.c 1997/08/02 14:32:11 1.7
+++ procfs_fpregs.c 1997/08/12 05:23:51 1.8
@@ -37,7 +37,7 @@
* @(#)procfs_fpregs.c 8.2 (Berkeley) 6/15/94
*
* From:
- * $Id: procfs_fpregs.c,v 1.7 1997/08/02 14:32:11 bde Exp $
+ * $Id: procfs_fpregs.c,v 1.8 1997/08/12 05:23:51 sef Exp $
*/
#include <sys/param.h>
@@ -60,6 +60,8 @@
char *kv;
int kl;
+ if (!CHECKIO(curp, p))
+ return EPERM;
kl = sizeof(r);
kv = (char *) &r;
(These patches can also be found on
ftp://freebsd.org/pub/CERT/patches/SA-97:04/)
VI. Thanks
This problem was brought to light by Brian Mitchell
<brian@firehouse.net>
=============================================================================
FreeBSD, Inc.
Web Site: http://www.freebsd.org/
Confidential contacts: security-officer@freebsd.org
PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications: security-notifications@freebsd.org
Security public discussion: security@freebsd.org
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.
=============================================================================
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