+cc Cong and Jiang, as potential users of AF_UNIX sockmap w/ unconnected SOCK_STREAM sockets https://lore.kernel.org/netdev/20231201180139.328529-1-john.fastabend@xxxxxxxxx/ From: John Fastabend <john.fastabend@xxxxxxxxx> Date: Mon, 04 Dec 2023 13:40:40 -0800 > Kuniyuki Iwashima wrote: > > From: John Fastabend <john.fastabend@xxxxxxxxx> > > Date: Fri, 1 Dec 2023 10:01:38 -0800 > > > I added logic to track the sock pair for stream_unix sockets so that we > > > ensure lifetime of the sock matches the time a sockmap could reference > > > the sock (see fixes tag). I forgot though that we allow af_unix unconnected > > > sockets into a sock{map|hash} map. > > > > > > This is problematic because previous fixed expected sk_pair() to exist > > > and did not NULL check it. Because unconnected sockets have a NULL > > > sk_pair this resulted in the NULL ptr dereference found by syzkaller. > > > > > > BUG: KASAN: null-ptr-deref in unix_stream_bpf_update_proto+0x72/0x430 net/unix/unix_bpf.c:171 > > > Write of size 4 at addr 0000000000000080 by task syz-executor360/5073 > > > Call Trace: > > > <TASK> > > > ... > > > sock_hold include/net/sock.h:777 [inline] > > > unix_stream_bpf_update_proto+0x72/0x430 net/unix/unix_bpf.c:171 > > > sock_map_init_proto net/core/sock_map.c:190 [inline] > > > sock_map_link+0xb87/0x1100 net/core/sock_map.c:294 > > > sock_map_update_common+0xf6/0x870 net/core/sock_map.c:483 > > > sock_map_update_elem_sys+0x5b6/0x640 net/core/sock_map.c:577 > > > bpf_map_update_value+0x3af/0x820 kernel/bpf/syscall.c:167 > > > > > > We considered just checking for the null ptr and skipping taking a ref > > > on the NULL peer sock. But, if the socket is then connected() after > > > being added to the sockmap we can cause the original issue again. So > > > instead this patch blocks adding af_unix sockets that are not in the > > > ESTABLISHED state. > > > > I'm not sure if someone has the unconnected stream socket use case > > though, can't we call additional sock_hold() in connect() by checking > > sk_prot under sk_callback_lock ? > > Could be done I guess yes. I'm not sure the utility of it though. I > thought above patch was the simplest solution and didn't require touching > main af_unix code. I don't actually use the sockmap with af_unix > sockets anywhere so maybe someone who is using this can comment if > unconnected is needed? > > From rcu and locking side looks like holding sk_callback_lock would > be sufficient. I was thinking it would require a rcu grace period > or something but seems not. > > I guess I could improve original patch if folks want. > > .John
