---------- Forwarded message ---------- Date: Thu, 12 Mar 1998 20:47:00 +0100 (MET) From: FreeBSD Security Officer <security-officerat_private>, FreeBSD Security Officer <security-officerat_private> To: freebsd-security-notificationsat_private, freebsd-announceat_private, freebsd-securityat_private, first-teamsat_private Subject: FreeBSD Security Advisory: FreeBSD-SA-98:02.mmap -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= 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" <tqbfat_private> for allowing this. Thanks to "Cy Schubert" <cschuberat_private> for porting the OpenBSD patch to FreeBSD. ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: security-officerat_private PGP Key: ftp://ftp.freebsd.org/pub/CERT/public_key.asc Security notifications: security-notificationsat_private Security public discussion: securityat_private 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: 2.6.2 iQCVAwUBNQg5QlUuHi5z0oilAQGxJQP/YRbQ4Ox0R7zELYIfiYY4ZTec53DlkNTm +NWLqqMJWFAQQ2BfTLmcxJdcaUlPkZmKU21ZUFVxKFuCjjp1MSiFApLJRcXuX6u6 ZYgwvrrLB5ppU2L/uWG+mlJKrf/j6R28B/NQ7b/OB9hcRlNdOFyu7K44M+yKxaPb SRJ4LR1rQKk= =qDrb -----END PGP SIGNATURE----- To Unsubscribe: send mail to majordomoat_private with "unsubscribe security" in the body of the message
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