CVE-2024-26923 af_unix: Fix garbage collector racing against connect()

2024-04-2421:49:22

Linux

www.cve.org

linux kernel

af_unix

sock_stream

vulnerability fix

garbage collector

embryo

scm_rights

inflight count

unix_gc_lock

7.7 High

AI Score

Confidence

High

0.0004 Low

EPSS

Percentile

13.1%

JSON

In the Linux kernel, the following vulnerability has been resolved:

af_unix: Fix garbage collector racing against connect()

Garbage collector does not take into account the risk of embryo getting
enqueued during the garbage collection. If such embryo has a peer that
carries SCM_RIGHTS, two consecutive passes of scan_children() may see a
different set of children. Leading to an incorrectly elevated inflight
count, and then a dangling pointer within the gc_inflight_list.

sockets are AF_UNIX/SOCK_STREAM
S is an unconnected socket
L is a listening in-flight socket bound to addr, not in fdtable
V’s fd will be passed via sendmsg(), gets inflight count bumped

connect(S, addr) sendmsg(S, [V]); close(V) __unix_gc()

NS = unix_create1()
skb1 = sock_wmalloc(NS)
L = unix_find_other(addr)
unix_state_lock(L)
unix_peer(S) = NS
// V count=1 inflight=0

		NS = unix_peer(S)
		skb2 = sock_alloc()
		skb_queue_tail(NS, skb2[V])

		// V became in-flight
		// V count=2 inflight=1

		close(V)

		// V count=1 inflight=1
		// GC candidate condition met

					for u in gc_inflight_list:
					  if (total_refs == inflight_refs)
					    add u to gc_candidates

					// gc_candidates={L, V}

					for u in gc_candidates:
					  scan_children(u, dec_inflight)

					// embryo (skb1) was not
					// reachable from L yet, so V's
					// inflight remains unchanged

__skb_queue_tail(L, skb1)
unix_state_unlock(L)
for u in gc_candidates:
if (u.inflight)
scan_children(u, inc_inflight_move_tail)

					// V count=1 inflight=2 (!)

If there is a GC-candidate listening socket, lock/unlock its state. This
makes GC wait until the end of any ongoing connect() to that socket. After
flipping the lock, a possibly SCM-laden embryo is already enqueued. And if
there is another embryo coming, it can not possibly carry SCM_RIGHTS. At
this point, unix_inflight() can not happen because unix_gc_lock is already
taken. Inflight graph remains unaffected.

CNA Affected

[
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "unaffected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/unix/garbage.c"
    ],
    "versions": [
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "a36ae0ec2353",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "343c5372d5e1",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "2e2a03787f4f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "e76c2678228f",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "b75722be422c",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "507cc232ffe5",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "dbdf7bec5c92",
        "status": "affected",
        "versionType": "git"
      },
      {
        "version": "1fd05ba5a2f2",
        "lessThan": "47d8ac011fe1",
        "status": "affected",
        "versionType": "git"
      }
    ]
  },
  {
    "product": "Linux",
    "vendor": "Linux",
    "defaultStatus": "affected",
    "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
    "programFiles": [
      "net/unix/garbage.c"
    ],
    "versions": [
      {
        "version": "2.6.23",
        "status": "affected"
      },
      {
        "version": "0",
        "lessThan": "2.6.23",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "4.19.314",
        "lessThanOrEqual": "4.19.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.4.275",
        "lessThanOrEqual": "5.4.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.10.216",
        "lessThanOrEqual": "5.10.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "5.15.156",
        "lessThanOrEqual": "5.15.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.1.87",
        "lessThanOrEqual": "6.1.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.6.28",
        "lessThanOrEqual": "6.6.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.8.7",
        "lessThanOrEqual": "6.8.*",
        "status": "unaffected",
        "versionType": "custom"
      },
      {
        "version": "6.9",
        "lessThanOrEqual": "*",
        "status": "unaffected",
        "versionType": "original_commit_for_fix"
      }
    ]
  }
]