Bug 2015046 (CVE-2021-3864)

Summary: CVE-2021-3864 kernel: descendant's dumpable setting with certain SUID binaries
Product: [Other] Security Response Reporter: Petr Matousek <pmatouse>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED NOTABUG QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: acaringi, adscvr, agladkov, airlied, alciregi, asavkov, bhu, brdeoliv, bskeggs, chwhite, crwood, ctoe, dbohanno, dhoward, dvlasenk, ebiederm, fhrbata, hdegoede, hkrzesin, jarod, jarodwilson, jburrell, jeremy, jforbes, jglisse, jlelli, joe.lawrence, jonathan, josef, jpoimboe, jshortt, jstancek, jthierry, jwboyer, kcarcia, kernel-maint, kernel-mgr, kpatch-maint, lgoncalv, linville, masami256, mchehab, nmurray, ptalbert, qzhao, rhandlin, rvrbovsk, security-response-team, steved, vkumar, walters, wcosta, williams, ycote
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in the way the dumpable flag setting was handled when certain SUID binaries executed its descendants. The prerequisite is a SUID binary that sets real UID equal to effective UID, and real GID equal to effective GID. The descendant will then have a dumpable value set to 1. As a result, if the descendant process crashes and core_pattern is set to a relative value, its core dump is stored in the current directory with uid:gid permissions. An unprivileged local user with eligible root SUID binary could use this flaw to place core dumps into root-owned directories, potentially resulting in escalation of privileges.
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Clone Of: Environment:
Last Closed: 2022-06-13 14:55:08 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2015893, 2015894, 2015895, 2015896, 2015897, 2015898, 2015899, 2015900, 2015901, 2015902, 2015982, 2015983, 2015984, 2015985, 2015986, 2015987    
Bug Blocks: 2010280    

Description Petr Matousek 2021-10-18 09:31:26 UTC 
A flaw was found in the way dumpable flag setting was handled when certain SUID binaries executed it's descendants. The prerequisite is a SUID binary that sets real uid equal to effective uid, and real gid equal to effective gid. Then the descendant will have a dumpable value set to 1. As a result, if the descendant process crashes and core_pattern is set to a relative value, it's core dump is stored in the current directory with uid:gid permissions. An unprivileged local user with eligible root suid binary could use this flaw to place core dumps into root owned directories potentially resulting in escalation of privileges.

Reference:
https://www.openwall.com/lists/oss-security/2021/10/20/2
Comment 6 Petr Matousek 2021-10-20 14:38:13 UTC 
Created kernel tracking bugs for this issue:

Affects: fedora-all [bug 2015987]
Comment 11 Wander 2021-12-28 17:17:39 UTC 
I proposed a patch in upstream for this bug https://lore.kernel.org/lkml/20211228170910.623156-1-wander@redhat.com/T/#t