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.
[
{
"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"
}
]
}
]
git.kernel.org/stable/c/2e2a03787f4f0abc0072350654ab0ef3324d9db3
git.kernel.org/stable/c/343c5372d5e17b306db5f8f3c895539b06e3177f
git.kernel.org/stable/c/47d8ac011fe1c9251070e1bd64cb10b48193ec51
git.kernel.org/stable/c/507cc232ffe53a352847893f8177d276c3b532a9
git.kernel.org/stable/c/a36ae0ec2353015f0f6762e59f4c2dbc0c906423
git.kernel.org/stable/c/b75722be422c276b699200de90527d01c602ea7c
git.kernel.org/stable/c/dbdf7bec5c920200077d693193f989cb1513f009
git.kernel.org/stable/c/e76c2678228f6aec74b305ae30c9374cc2f28a51