Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2000.115 -- NetBSD Security Advisory 2000-004 SysV semaphore denial-of-service 01 June 2000 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: NetBSD kernel Vendor: NetBSD Operating System: NetBSD FreeBSD Unix Platform: N/A Impact: Denial of Service Access Required: Local Ref: ESB-2000.110 - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- NetBSD Security Advisory 2000-004 ================================= Topic: SysV semaphore denial-of-service Version: all prior to 2000/05/27 Severity: minor (local denial of service to programs using the rarely-used semaphore facility) Abstract ======== An undocumented system call permits any user process to lock up the entire semaphore subsystem, preventing processes using semaphores from locking or unlocking them, and preventing processes holding semaphores from exiting. Note: FreeBSD-SA-00:19 describes a similar, but significantly more severe problem affecting FreeBSD, and notes that NetBSD is also affected. The impact of the problem on NetBSD is much less, because NetBSD's semaphore implementation was fixed (in 1994) so that only semaphore-using processes would be blocked at exit time. Technical Details ================= The undocumented semconfig(2) system call is used by ipcs(1) to "freeze" the state of semaphores so that a self-consistant snapshot could be displayed. However, this could then be abused to lock the semaphore system, preventing all semaphore operations from progressing, and leave it locked until the locking process exited. The fix is to disable this unnecessary locking; other comparable /dev/kmem-reading programs such as ps(1) and netstat(1) have never needed this sort of locking. Solutions and Workarounds ========================= Only programs which make use of semaphores are affected by this problem. If you are unsure if any applications use semaphores, use the ipcs(1) command; if it displays more than simple column headers, there is active use of semaphores on your system. For example: % ipcs -s Semaphores: T ID KEY MODE OWNER GROUP s 524288 -1 --rw------- wes wheel Note that this test is not 100% conclusive; however, use of System V semaphores is extremely rare. If you determine that your system may run programs which use semaphore you should patch your kernel as follows: For formal NetBSD releases, you should to download the appropriate source patch listed below, apply it to your kernel source tree using the patch(1) command. For NetBSD-current, you should update your source tree (with either sup or anonymous CVS). In both cases, you then need to rebuild, install the newly built kernel, and reboot. For more information on how to do this, see: http://www.netbsd.org/Documentation/kernel/#building_a_kernel For NetBSD 1.4, 1.4.1, and 1.4.2: A patch is available in ftp://ftp.NetBSD.ORG/pub/NetBSD/misc/security/patches/20000527-sysvsem For NetBSD-current: NetBSD-current since 20000527 contains all the fixes, and is not vulnerable. Users of NetBSD-current should upgrade to a source tree dated 20000527 or later. Thanks To ========= The FreeBSD security officer, for bringing the problem to our attention. Bill Sommerfeld for coding and testing the fix. Revision History ================ 2000/05/27 - initial version. More Information ================ Information about NetBSD and NetBSD security can be found at http://www.NetBSD.ORG/ and http://www.NetBSD.ORG/Security/. Copyright 2000, The NetBSD Foundation, Inc. All Rights Reserved. $NetBSD: NetBSD-SA2000-004.txt,v 1.3 2000/05/29 01:01:11 sommerfeld Exp $ - -----BEGIN PGP SIGNATURE----- Version: 2.6.3ia Charset: noconv iQCVAwUBOTHBbD5Ru2/4N2IFAQG1zQP+LYnjsZzLPKKSur1ywCsZQN+kqt3wpVa+ qP3pTcCTDbrh7QbwwTibzkGo5h7dnbwVGYHP0yGSDpVmRN//q+sOo5g92NMqC5Bn iodYJPyE5pu3IJrKtSCQOIddUV49TKRV7NnQVHTJIEfxxbgRWRjlbNAwLS7qscV3 Gc8JOKs0ev0= =KhiA - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. 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. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the original authors to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. 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: firstname.lastname@example.org Facsimile: (07) 3365 7031 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. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBOXXS7yh9+71yA2DNAQF5ZQP+MDJMNUqVMw99/B2AmuftaM1yigFVLVn4 D4F68WHTP4v2jSEnaJ0R7apgDLAEWi4BdmFNcGEVN1v4fN+N8W4P+xa4yXnGL82l r5ay46CY7vrm7TMvXlHKJFiqvzyatkBhLtk2Ehi5NG4eByD0j1m9JHM7CZBXyIAH azRH1PBTCYw= =KQ70 -----END PGP SIGNATURE-----