NetBSD Security Advisory 2022-004: procfs(5) missing permission checks
4 October, 2022 by security-officer@netbsd.org | netbsd
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 NetBSD Security Advisory 2022-004 ================================= Topic: procfs(5) missing permission checks Version: NetBSD-current: affected prior to 2022-06-18 NetBSD 9.2: affected NetBSD 8.2: affected Severity: Malicious user may read from opened file descriptors by other processes. Fixed: NetBSD-current: June 17, 2022 NetBSD-9 branch: June 17, 2022 NetBSD-8 branch: June 17, 2022 Please note that NetBSD releases prior to 8 are no longer supported. It is recommended that all users upgrade to a supported release. Abstract ======== Due to missing permission checks it was possible to reuse open descriptors which are exposed in the procfs(5) [pid]/fd/ directory. It might allow malicious user to bypass permission checks and read data from opened descriptor under some circumstances. Technical Details ================= Directory fd/ which is available per process in the procfs(5) is exposing all opened file descriptors by a process, because of the missing VOP_ACCESS check during the VOP_LOOKUP(9) operation. Due to lack of proper access verification, malicious user is allowed to open files from the directory with the file descriptors, because permissions of the directory are not effectively checked. An example scenario that leads to data leak is as follows: the file with permissions 644 protected by the directory permissions 700, if process opened the file, it is possible to obtain file descriptor by malicious user by opening it directly from the exposed fd/ folder by the procfs(5). Solutions and Workarounds ========================= Immediate workaround: unmount procfs(5) and mark it "noauto" in /etc/fstab. Please note that some programs may need access to procfs(5) in order to work correctly. To apply a fixed version from a releng build, fetch a fitting kern-GENERIC.tgz from nycdn.NetBSD.org and extract the fixed binaries: cd /var/tmp ftp https://nycdn.NetBSD.org/pub/NetBSD-daily/REL/BUILD/ARCH/binary/sets/kern-GENERIC.tgz cd / tar xzpf /var/tmp/kern-GENERIC.tgz with the following replacements: REL = the release version you are using BUILD = the source date of the build. 20220618 and later will fit ARCH = your system's architecture The following instructions describe how to upgrade your kernel by updating your source tree and rebuilding and installing a new version of the kernel. For all NetBSD versions, you need to obtain fixed kernel sources, rebuild and install the new kernel, and reboot the system. The fixed source may be obtained from the NetBSD CVS repository. The following instructions briefly summarise how to upgrade your kernel. In these instructions, replace: ARCH with your architecture (from uname -m), and KERNCONF with the name of your kernel configuration file. To update from CVS, re-build, and re-install the kernel: # cd src # cvs update -d -P sys/miscfs/procfs/procfs_vnops.c # ./build.sh kernel=KERNCONF # mv /netbsd /netbsd.old # cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd # shutdown -r now For more information on how to do this, see: https://www.NetBSD.org/docs/guide/en/chap-kernel.html Thanks To ========= Mateusz Kocielski (shm@) who analyzed this problem and supplied the fixes. Revision History ================ 2022-10-04 Initial release More Information ================ Advisories may be updated as new information becomes available. The most recent version of this advisory (PGP signed) can be found at https://cdn.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2022-004.txt.asc Information about NetBSD and NetBSD security can be found at https://www.NetBSD.org/ https://www.NetBSD.org/support/security/ Copyright 2022, The NetBSD Foundation, Inc. All Rights Reserved. Redistribution permitted only in full, unmodified form. $Id: NetBSD-SA2022-004.txt,v 1.1 2022/10/04 13:48:36 christos Exp $ -----BEGIN PGP SIGNATURE----- iQJQBAEBCAA6FiEEJxEzJivzXLUNT1BGiSYeF/XvSf8FAmM8ObUcHHNlY3VyaXR5 LW9mZmljZXJAbmV0YnNkLm9yZwAKCRCJJh4X9e9J/4rlD/4lMc/pDB1lCqQdaVD4 SVdQCZN7j/V2R8Nt/iXRtigOCo8gzX1Y/vmJwpTCqf1G8rTRChjH3p+arHgOHvDJ jNBevmoG8Dmy3YSJmsWAiMcsMHiEwvD/sXKkzwWDXQHILklezQIEj6UIHqOOuG5+ n92HwNLvhBL7d96dRFrmKoaqjVN6X4DyCzrxdk3DD8+boc0Gyv+69I6uxwML538M EiC6x0k2ccwfwC3jhRGdvr1DeBoVLev+p6d88yHisFXDnRRCK3AzryvGr8jf+QJr KbPBZlW13FpRsBEa6pRzMArMT7u7LoDedyzL6bdKdVplgBkq/CLCl5mkfID0TIba EIh2tQwMWrk8zkrCXWqqnOxJgjremlm78lryCc2UTwIblZ+73wuAYz36hNAU1xed GN9xV59ydjOFJunf00RWoAURpOP6629Cli2Pb3DVrZGJrMjNV2TyGol2+lERCK7v dDCQFfF3616xPDys+7bKNGhlMu7Wd0Eo5eVuqGwAoHtL8hbjshW+iS0h0/nmxFJA T0klPZk/m3kQbRjXYR0dl1rd5fhdFLhTo9aFWf5YbgYbKQbKRlg16ejAjg/m29vC f8R5mL3IHovX5fK/QvkOX7fnbe91EmJf19PmtyuLCYfVdNou7DjYFu33HWTRHf5m 7rN8Ns3I5Ty1hSPn9XtWoW5N6Q== =G+yI -----END PGP SIGNATURE-----