Date: Wed, 3 Jun 1998 19:44:29 +0200 (MET DST) From: FreeBSD Security Officer <security-officerat_private> To: undisclosed-recipients:;@FreeBSD.ORG Subject: FreeBSD Security Advisory: FreeBSD-SA-98:04.mmap -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-98:04 Security Advisory FreeBSD, Inc. Topic: security compromise via mmap Category: core Module: kernel Announced: 1998-06-02 Affects: FreeBSD 2.2.*, FreeBSD-stable before 1998/05/24 and FreeBSD-current before 1998/05/19 suffer from this problem. Corrected: FreeBSD-current as of 1998/05/19 FreeBSD-stable as of 1998/05/24 FreeBSD only: no (also other 4.4BSD based systems may be affected) Patches: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-98:04/ ============================================================================= IMPORTANT MESSAGE: The FreeBSD security officer now uses the policy ftp://freebsd.org/pub/CERT to ftp://ftp.freebsd.org/pub/FreeBSD/POLICY for sending out advisories. ============================================================================= 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. In 4.4BSD, 4 new FFS flags were added that give the possibility to mark files as append-only or immutable. II. Problem Description It is possible for a process to open an append-only file according to the limitations of the flags, and then mmap the file shared with write permission even when the file is marked as append-only or immutable. This circumvents the concept of the the append-only flag. III. Impact It is possible to change the contents of append-only files. 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/FreeBSD/CERT/patches/SA-98:04/ NOTE: Users of FreeBSD 2.2.5 or FreeBSD-current or FreeBSD-stable dated before 1998/03/12 will need to apply the patch mentioned in FreeBSD advisory 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 1.75 retrieving revision 1.77 diff -u -r1.75 -r1.77 --- vm_mmap.c 1998/03/12 19:36:18 1.75 +++ vm_mmap.c 1998/05/19 07:13:21 1.77 @@ -58,6 +58,7 @@ #include <sys/file.h> #include <sys/mman.h> #include <sys/conf.h> +#include <sys/stat.h> #include <sys/vmmeter.h> #include <miscfs/specfs/specdev.h> @@ -295,12 +296,25 @@ * 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 + + if ((flags & MAP_SHARED) != 0 || + (vp->v_type == VCHR && disablexworkaround)) { + if ((fp->f_flag & FWRITE) != 0) { + struct vattr va; + if ((error = + VOP_GETATTR(vp, &va, + p->p_ucred, p))) + return (error); + if ((va.va_flags & + (IMMUTABLE|APPEND)) == 0) + maxprot |= VM_PROT_WRITE; + else if (prot & PROT_WRITE) + return (EPERM); + } else if ((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 1.53.2.3 retrieving revision 1.53.2.4 diff -u -r1.53.2.3 -r1.53.2.4 --- vm_mmap.c 1998/03/12 19:36:50 1.53.2.3 +++ vm_mmap.c 1998/05/24 19:47:02 1.53.2.4 @@ -57,6 +57,7 @@ #include <sys/file.h> #include <sys/mman.h> #include <sys/conf.h> +#include <sys/stat.h> #include <sys/vmmeter.h> #include <miscfs/specfs/specdev.h> @@ -275,12 +276,26 @@ * 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 + + if ((flags & MAP_SHARED) != 0 || + (vp->v_type == VCHR && disablexworkaround)) { + if ((fp->f_flag & FWRITE) != 0) { + struct vattr va; + + if ((error = + VOP_GETATTR(vp, &va, + p->p_ucred, p))) + return (error); + if ((va.va_flags & + (IMMUTABLE|APPEND)) == 0) + maxprot |= VM_PROT_WRITE; + else if (prot & PROT_WRITE) + return (EPERM); + } else if ((prot & PROT_WRITE) != 0) + return (EACCES); + } else maxprot |= VM_PROT_WRITE; + handle = (caddr_t) vp; } } VI. Thanks This advisory is based on NetBSD Security Advisory 1998-003. In porting the NetBSD patch, we accidentally mentioned that we obtained the patch from OpenBSD, which was evidently wrong. ============================================================================= FreeBSD, Inc. Web Site: http://www.freebsd.org/ Confidential contacts: security-officerat_private Security notifications: security-notificationsat_private Security public discussion: freebsd-securityat_private 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 iQCVAwUBNXWJC1UuHi5z0oilAQG3nAP9GjmOtlc1WxPJjcbRwvXmKzhRInCfuVTL f5k7dAyFmUmo6wnyQwsBoQUsa7d/kS0YCnfTIkFYrGkFvBa8hnw/i9VVdMFaUFFV kTo6YLQfgG35znTxftACAs4uzjeRbh/6dr1YsERYxWNW0PabKbYfjMQapmY5GUVm px3WF/jRI5k= =Umgx -----END PGP SIGNATURE----- To Unsubscribe: send mail to majordomoat_private with "unsubscribe security" in the body of the message
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