Description

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_ca...

Classification

CVE ID: CVE-2024-26923

Affected Products

Vendor: Linux

Product: Linux

Exploit Prediction Scoring System (EPSS)

EPSS Score: 0.04% (probability of being exploited)

EPSS Percentile: 15.26% (scored less or equal to compared to others)

EPSS Date: 2025-02-04 (when was this score calculated)

References

https://git.kernel.org/stable/c/a36ae0ec2353015f0f6762e59f4c2dbc0c906423
https://git.kernel.org/stable/c/343c5372d5e17b306db5f8f3c895539b06e3177f
https://git.kernel.org/stable/c/2e2a03787f4f0abc0072350654ab0ef3324d9db3
https://git.kernel.org/stable/c/e76c2678228f6aec74b305ae30c9374cc2f28a51
https://git.kernel.org/stable/c/b75722be422c276b699200de90527d01c602ea7c
https://git.kernel.org/stable/c/507cc232ffe53a352847893f8177d276c3b532a9
https://git.kernel.org/stable/c/dbdf7bec5c920200077d693193f989cb1513f009
https://git.kernel.org/stable/c/47d8ac011fe1c9251070e1bd64cb10b48193ec51

Timeline