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author | Michal Luczaj <mhal@rbox.co> | 2024-04-09 23:09:39 +0300 |
---|---|---|
committer | Paolo Abeni <pabeni@redhat.com> | 2024-04-11 10:46:15 +0300 |
commit | 47d8ac011fe1c9251070e1bd64cb10b48193ec51 (patch) | |
tree | 1943dbd2c188967b99c1ff56835957f1fb5b3123 /include | |
parent | 17c560113231ddc20088553c7b499b289b664311 (diff) | |
download | linux-47d8ac011fe1c9251070e1bd64cb10b48193ec51.tar.xz |
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.
Fixes: 1fd05ba5a2f2 ("[AF_UNIX]: Rewrite garbage collector, fixes race.")
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20240409201047.1032217-1-mhal@rbox.co
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Diffstat (limited to 'include')
0 files changed, 0 insertions, 0 deletions