****************************************************************************** ------ ----- ----- --- ----- | ----- ---- | | | | | |--- | | | | | | | | | |-- | | | | |-- | | | | | | | | \ | | ----- ---- ----- ----- | \ ----- A D V I S O R Y FA-98.24 ****************************************************************************** Topic: Security compromise via mmap Source: CIAC Creation Date: March 16, 1998 Last Updated: To aid in the wide distribution of essential security information, FedCIRC is forwarding the following information from CIAC bulletin I-037. FedCIRC urges you to act on this information as soon as possible. If you have any questions, please contact FedCIRC: Telephone: +1 888 282 0870 Email: fedcirc@fedcirc.gov =======================FORWARDED TEXT STARTS HERE============================ -----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN FreeBSD mmap Vulnerability March 16, 1998 23:00 GMT Number I-037 ______________________________________________________________________________ PROBLEM: A vulnerability exists in the 4.4BSD VM system which allows files to be "memory mapped". PLATFORM: FreeBSD 2.2.*, FreeBSD-stable and FreeBSD-current before 1998/03/11. DAMAGE: If exploited, unauthorized users may gain root access. SOLUTION: Apply patches listed below. ______________________________________________________________________________ VULNERABILITY FreeBSD recommends that the patches be applied on affected ASSESSMENT: systems. ______________________________________________________________________________ [ Start FreeBSD, Inc. Advisory ] ============================================================================= FreeBSD-SA-98:02 Security Advisory FreeBSD, Inc. Topic: security compromise via mmap Category: core Module: kernel Announced: 1998-03-12 Affects: FreeBSD 2.2.*, FreeBSD-stable and FreeBSD-current before 1998/03/11 suffer from this problem. Corrected: FreeBSD-current as of 1998/03/11 FreeBSD-stable as of 1998/03/11 FreeBSD only: no (also other 4.4BSD based systems may be affected) Patches: ftp://ftp.freebsd.org/pub/CERT/patches/SA-98:02/ ============================================================================= IMPORTANT MESSAGE: The FreeBSD advisory archive has moved from ftp://freebsd.org/pub/CERT to ftp://ftp.freebsd.org/pub/CERT ============================================================================= I. Background The 4.4BSD VM system allows files to be "memory mapped", which causes the specified contents of a file to be made available to a process via its address space. Manipulations of that file can then be performed simply by manipulating memory, rather than using filesystem I/O calls. This technique is used to simplify code, speed up access to files, and provide interprocess communication. II. Problem Description Due to a 4.4BSD VM system problem, it is possible to memory-map a read-only descriptor to a character device in read-write mode. III. Impact The hole can be used by members of group kmem to gain superuser privileges. It also allows the superuser to lower the system securelevel. IV. Workaround No workaround is known. V. Solution Apply one of the following patches, rebuild your kernel, install it and reboot your system. The patches below can be found on ftp://ftp.freebsd.org/pub/CERT/patches/SA-98:02/ Patch for 3.0-current systems: Index: vm_mmap.c =================================================================== RCS file: /home/cvsup/freebsd/CVS/src/sys/vm/vm_mmap.c,v retrieving revision 1.74 diff -u -r1.74 vm_mmap.c --- vm_mmap.c 1998/03/07 21:37:01 1.74 +++ vm_mmap.c 1998/03/10 21:51:30 @@ -162,6 +162,7 @@ vm_prot_t prot, maxprot; void *handle; int flags, error; + int disablexworkaround; off_t pos; addr = (vm_offset_t) uap->addr; @@ -252,6 +253,26 @@ pos = 0; } else { /* + * cdevs does not provide private mappings of any kind. + */ + /* + * However, for XIG X server to continue to work, + * we should allow the superuser to do it anyway. + * We only allow it at securelevel < 1. + * (Because the XIG X server writes directly to video + * memory via /dev/mem, it should never work at any + * other securelevel. + * XXX this will have to go + */ + if (securelevel >= 1) + disablexworkaround = 1; + else + disablexworkaround = suser(p->p_ucred, + &p->p_acflag); + if (vp->v_type == VCHR && disablexworkaround && + (flags & (MAP_PRIVATE|MAP_COPY))) + return (EINVAL); + /* * Ensure that file and memory protections are * compatible. Note that we only worry about * writability if mapping is shared; in this case, @@ -265,12 +286,20 @@ maxprot |= VM_PROT_READ; else if (prot & PROT_READ) return (EACCES); - if (flags & MAP_SHARED) { - if (fp->f_flag & FWRITE) - maxprot |= VM_PROT_WRITE; - else if (prot & PROT_WRITE) - return (EACCES); - } else + /* + * If we are sharing potential changes (either via + * MAP_SHARED or via the implicit sharing of character + * device mappings), and we are trying to get write + * permission although we opened it without asking + * for it, bail out. Check for superuser, only if + * we're at securelevel < 1, to allow the XIG X server + * to continue to work. + */ + if (((flags & MAP_SHARED) != 0 || + (vp->v_type == VCHR && disablexworkaround)) && + (fp->f_flag & FWRITE) == 0 && (prot & PROT_WRITE) != 0) + return (EACCES); + else maxprot |= VM_PROT_WRITE; handle = (void *)vp; } Patch for 2.2 systems: Index: vm_mmap.c =================================================================== RCS file: /home/cvsup/freebsd/CVS/src/sys/vm/vm_mmap.c,v retrieving revision 1.53.2.2 diff -u -r1.53.2.2 vm_mmap.c --- vm_mmap.c 1997/03/25 04:54:29 1.53.2.2 +++ vm_mmap.c 1998/03/10 21:50:46 @@ -157,6 +157,9 @@ vm_prot_t prot, maxprot; caddr_t handle; int flags, error; + int disablexworkaround; + + addr = (vm_offset_t) uap->addr; prot = uap->prot & VM_PROT_ALL; flags = uap->flags; @@ -230,6 +233,26 @@ flags |= MAP_ANON; } else { /* + * cdevs does not provide private mappings of any kind. + */ + /* + * However, for XIG X server to continue to work, + * we should allow the superuser to do it anyway. + * We only allow it at securelevel < 1. + * (Because the XIG X server writes directly to video + * memory via /dev/mem, it should never work at any + * other securelevel. + * XXX this will have to go + */ + if (securelevel >= 1) + disablexworkaround = 1; + else + disablexworkaround = suser(p->p_ucred, + &p->p_acflag); + if (vp->v_type == VCHR && disablexworkaround && + (flags & (MAP_PRIVATE|MAP_COPY))) + return (EINVAL); + /* * Ensure that file and memory protections are * compatible. Note that we only worry about * writability if mapping is shared; in this case, @@ -243,12 +266,20 @@ maxprot |= VM_PROT_READ; else if (prot & PROT_READ) return (EACCES); - if (flags & MAP_SHARED) { - if (fp->f_flag & FWRITE) - maxprot |= VM_PROT_WRITE; - else if (prot & PROT_WRITE) - return (EACCES); - } else + /* + * If we are sharing potential changes (either via + * MAP_SHARED or via the implicit sharing of character + * device mappings), and we are trying to get write + * permission although we opened it without asking + * for it, bail out. Check for superuser, only if + * we're at securelevel < 1, to allow the XIG X server + * to continue to work. + */ + if (((flags & MAP_SHARED) != 0 || + (vp->v_type == VCHR && disablexworkaround)) && + (fp->f_flag & FWRITE) == 0 && (prot & PROT_WRITE) != 0) + return (EACCES); + else maxprot |= VM_PROT_WRITE; handle = (caddr_t) vp; } VI. Thanks This advisory is based on the OpenBSD Security Advisory, dated February 20 2, 1998. Thanks to "Thomas H. Ptacek" for allowing this. Thanks to "Cy Schubert" for porting the OpenBSD patch to FreeBSD. ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: security-officer@freebsd.org PGP Key: ftp://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. ============================================================================= [ End FreeBSD, Inc. Advisory ] ______________________________________________________________________________ CIAC wishes to acknowledge the contributions of FreeBSD, Inc. for the information contained in this bulletin. ______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. 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This is a partial protection to make sure you are really the one who asked to be signed up for the list in question. If you include the word 'help' in the body of an email to the above address, it will also send back an information file on how to subscribe/unsubscribe, get past issues of CIAC bulletins via email, etc. PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) I-027B: HP-UX Vulnerabilities (CUE, CDE, land) I-028: Vulnerabilities in CDE I-029: IBM AIX Telnet Denial-of-Service Vulnerability I-030: SunOS volrmmount (1) Vulnerability I-031A: WindowsNT-95 Attacks on DOE Sites I-032: Sun Solaris Vulnerabilities (vacation, dtaction) I-033: Sun Solaris Vulnerabilities (ndd, rpc.cmsd) I-034: Internet Cookies I-035: SGI Vulnerabilities I-036: FreeBSD Denial-of Service LAND Attacks -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBNRAT27nzJzdsy3QZAQFBqAQAxtOvgxwMpvapcKwN9IT6QujKXYQY6N9r EFHvlXwbHL5iqEG/Ch3NV8NsjJm462uteG+x7ORwuBT3huwYtikk9mGmchbF9Ct7 bV8rS2w/n+DAK3F5u6qtjoA9KBksqUC5NpFcOLR3Ais5t+/VCb/RvT2kvWu/ewKf +iBnRsY9prY= =R5Hg -----END PGP SIGNATURE----- ========================FORWARDED TEXT ENDS HERE============================= The National Institute of Standards and Technology (NIST) has established a Federal Computer Incident response Capability (FedCIRC) to assist federal civilians agencies in their incident handling efforts by providing proactive and reactive computer security related services. FedCIRC is a partnership among NIST, the Computer Incident Advisory Capability (CIAC), and the CERT* Coordination Center (CERT/CC). If you believe that your system has been compromised, please contact FedCIRC: Telephone: +1 888 282 0870 Email: fedcirc@fedcirc.gov Web Server: http://www.fedcirc.gov/ * Registered in U.S. Patent and Trademark Office The CERT Coordination Center is part of the Software Engineering Institute. The Software Engineering Institute is sponsored by the U.S. Department of Defense. CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes.