> -----Original Message----- > From: John Fastabend [mailto:john.fastabend@xxxxxxxxx] > Sent: Tuesday, August 9, 2022 2:58 PM > To: liujian (CE) <liujian56@xxxxxxxxxx>; john.fastabend@xxxxxxxxx; > jakub@xxxxxxxxxxxxxx; davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx; > kuba@xxxxxxxxxx; pabeni@xxxxxxxxxx; daniel@xxxxxxxxxxxxx; > andrii@xxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx > Cc: liujian (CE) <liujian56@xxxxxxxxxx> > Subject: RE: [PATCH bpf-next] skmsg: Fix wrong last sg check in > sk_msg_recvmsg() > > Liu Jian wrote: > > Fix one kernel NULL pointer dereference as below: > > > > [ 224.462334] Call Trace: > > [ 224.462394] __tcp_bpf_recvmsg+0xd3/0x380 [ 224.462441] ? > > sock_has_perm+0x78/0xa0 [ 224.462463] tcp_bpf_recvmsg+0x12e/0x220 [ > > 224.462494] inet_recvmsg+0x5b/0xd0 [ 224.462534] > > __sys_recvfrom+0xc8/0x130 [ 224.462574] ? > > syscall_trace_enter+0x1df/0x2e0 [ 224.462606] ? > > __do_page_fault+0x2de/0x500 [ 224.462635] > > __x64_sys_recvfrom+0x24/0x30 [ 224.462660] do_syscall_64+0x5d/0x1d0 > > [ 224.462709] entry_SYSCALL_64_after_hwframe+0x65/0xca > > > > In commit 7303524e04af ("skmsg: Lose offset info in > > sk_psock_skb_ingress"), we change last sg check to sg_is_last(), but > > in sockmap redirection case (without > > stream_parser/stream_verdict/skb_verdict), we did not mark the end of > > the scatterlist. Check the sk_msg_alloc, sk_msg_page_add, and > > bpf_msg_push_data functions, they all do not mark the end of sg. They > > are expected to use sg.end for end judgment. So the judgment of '(i != > msg_rx->sg.end)' is added back here. > > > > Fixes: 7303524e04af ("skmsg: Lose offset info in > > sk_psock_skb_ingress") > > Signed-off-by: Liu Jian <liujian56@xxxxxxxxxx> > > --- > > This is the wrong fixes tag though right? We should have, I am sorry for this, and will send v2 to update the fix tag. > > 9974d37ea75f0 ("skmsg: Fix invalid last sg check in sk_msg_recvmsg()") > > Fix looks OK though although its not great we have two ways to find the last > frag now. I'm going to look at getting some better testing in place and then > see if we can get to just one check. > > Assuming I'm right on the fixes tag please update that. > > > net/core/skmsg.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/net/core/skmsg.c b/net/core/skmsg.c index > > 81627892bdd4..385ae23580a5 100644 > > --- a/net/core/skmsg.c > > +++ b/net/core/skmsg.c > > @@ -462,7 +462,7 @@ int sk_msg_recvmsg(struct sock *sk, struct > > sk_psock *psock, struct msghdr *msg, > > > > if (copied == len) > > break; > > - } while (!sg_is_last(sge)); > > + } while ((i != msg_rx->sg.end) && !sg_is_last(sge)); > > > > if (unlikely(peek)) { > > msg_rx = sk_psock_next_msg(psock, msg_rx); @@ - > 472,7 +472,7 @@ int > > sk_msg_recvmsg(struct sock *sk, struct sk_psock *psock, struct msghdr > *msg, > > } > > > > msg_rx->sg.start = i; > > - if (!sge->length && sg_is_last(sge)) { > > + if (!sge->length && (i == msg_rx->sg.end || sg_is_last(sge))) > { > > msg_rx = sk_psock_dequeue_msg(psock); > > kfree_sk_msg(msg_rx); > > } > > -- > > 2.17.1 > > >
