DEBIAN-CVE-2024-26923

In the Linux kernel, the following vulnerability has been resolved: afunix: 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 SCMRIGHTS, two consecutive passes of scanchildren() may see a different set of children. Leading to an incorrectly elevated inflight count, and then a dangling pointer within the gcinflightlist. sockets are AFUNIX/SOCKSTREAM 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) _unixgc() ---------------- ------------------------- ----------- NS = unixcreate1() skb1 = sockwmalloc(NS) L = unixfindother(addr) unixstatelock(L) unixpeer(S) = NS // V count=1 inflight=0 NS = unixpeer(S) skb2 = sockalloc() skbqueuetail(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 gcinflightlist: if (totalrefs == inflightrefs) add u to gccandidates // gccandidates={L, V} for u in gccandidates: scanchildren(u, decinflight) // embryo (skb1) was not // reachable from L yet, so V's // inflight remains unchanged _skbqueuetail(L, skb1) unixstateunlock(L) for u in gccandidates: if (u.inflight) scanchildren(u, incinflightmovetail) // 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 SCMRIGHTS. At this point, unixinflight() can not happen because unixgc_lock is already taken. Inflight graph remains unaffected.