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[35.245.174.172]) by smtp.gmail.com with ESMTPSA id j15-20020a37ef0f000000b007468bf8362esm94219qkk.66.2023.04.19.19.20.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Apr 2023 19:20:07 -0700 (PDT) Date: Wed, 19 Apr 2023 22:20:07 -0400 From: Willem de Bruijn To: Kuniyuki Iwashima , willemdebruijn.kernel@gmail.com Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, kuni1840@gmail.com, kuniyu@amazon.com, netdev@vger.kernel.org, pabeni@redhat.com, syzkaller@googlegroups.com, willemb@google.com Message-ID: <6440a157b6113_128322942d@willemb.c.googlers.com.notmuch> In-Reply-To: <20230419224358.98442-1-kuniyu@amazon.com> References: <644029f7e7814_38cc8429476@willemb.c.googlers.com.notmuch> <20230419224358.98442-1-kuniyu@amazon.com> Subject: Re: [PATCH v2 net] tcp/udp: Fix memleaks of sk and zerocopy skbs with TX timestamp. Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Kuniyuki Iwashima wrote: > From: Willem de Bruijn > Date: Wed, 19 Apr 2023 13:50:47 -0400 > > Kuniyuki Iwashima wrote: > > > From: Willem de Bruijn > > > Date: Wed, 19 Apr 2023 10:16:07 -0400 > > > > Eric Dumazet wrote: > > > > > On Tue, Apr 18, 2023 at 9:25=E2=80=AFPM Kuniyuki Iwashima wrote: > > > > > > > > > > > > From: Eric Dumazet > > > > > > Date: Tue, 18 Apr 2023 21:04:32 +0200 > > > > > > > On Tue, Apr 18, 2023 at 8:44=E2=80=AFPM Kuniyuki Iwashima <= kuniyu@amazon.com> wrote: > > > > > > > > > > > > > > > > From: Eric Dumazet > > > > > > > > Date: Tue, 18 Apr 2023 20:33:44 +0200 > > > > > > > > > On Tue, Apr 18, 2023 at 8:09=E2=80=AFPM Kuniyuki Iwashi= ma wrote: > > > > > > > > > > > > > > > > > > > > syzkaller reported [0] memory leaks of an UDP socket = and ZEROCOPY > > > > > > > > > > skbs. We can reproduce the problem with these sequen= ces: > > > > > > > > > > > > > > > > > > > > sk =3D socket(AF_INET, SOCK_DGRAM, 0) > > > > > > > > > > sk.setsockopt(SOL_SOCKET, SO_TIMESTAMPING, SOF_TIME= STAMPING_TX_SOFTWARE) > > > > > > > > > > sk.setsockopt(SOL_SOCKET, SO_ZEROCOPY, 1) > > > > > > > > > > sk.sendto(b'', MSG_ZEROCOPY, ('127.0.0.1', 53)) > > > > > > > > > > sk.close() > > > > > > > > > > > > > > > > > > > > sendmsg() calls msg_zerocopy_alloc(), which allocates= a skb, sets > > > > > > > > > > skb->cb->ubuf.refcnt to 1, and calls sock_hold(). He= re, struct > > > > > > > > > > ubuf_info_msgzc indirectly holds a refcnt of the sock= et. When the > > > > > > > > > > skb is sent, __skb_tstamp_tx() clones it and puts the= clone into > > > > > > > > > > the socket's error queue with the TX timestamp. > > > > > > > > > > > > > > > > > > > > When the original skb is received locally, skb_copy_u= bufs() calls > > > > > > > > > > skb_unclone(), and pskb_expand_head() increments skb-= >cb->ubuf.refcnt. > > > > > > > > > > This additional count is decremented while freeing th= e skb, but struct > > > > > > > > > > ubuf_info_msgzc still has a refcnt, so __msg_zerocopy= _callback() is > > > > > > > > > > not called. > > > > > > > > > > > > > > > > > > > > The last refcnt is not released unless we retrieve th= e TX timestamped > > > > > > > > > > skb by recvmsg(). When we close() the socket holding= such skb, we > > > > > > > > > > never call sock_put() and leak the count, skb, and sk= . > > > > > > > > > > > > > > > > > > > > To avoid this problem, we must (i) call skb_queue_pur= ge() after > > > > > > > > > > flagging SOCK_DEAD during close() and (ii) make sure = that TX tstamp > > > > > > > > > > skb is not queued when SOCK_DEAD is flagged. UDP lac= ks (i) and (ii), > > > > > > > > > > and TCP lacks (ii). > > > > > > > > > > > > > > > > > > > > Without (ii), a skb queued in a qdisc or device could= be put into > > > > > > > > > > the error queue after skb_queue_purge(). > > > > > > > > > > > > > > > > > > > > sendmsg() /* return immediately, but packets > > > > > > > > > > * are queued in a qdisc or device > > > > > > > > > > */ > > > > > > > > > > close() > > > > > > > > > > skb_queue_purge= () > > > > > > > > > > __skb_tstamp_tx() > > > > > > > > > > __skb_complete_tx_timestamp() > > > > > > > > > > sock_queue_err_skb() > > > > > > > > > > skb_queue_tail() > > > > > > > > > > > > > > > > > > > > Also, we need to check SOCK_DEAD under sk->sk_error_q= ueue.lock > > > > > > > > > > in sock_queue_err_skb() to avoid this race. > > > > > > > > > > > > > > > > > > > > if (!sock_flag(sk, SOCK_DEAD)) > > > > > > > > > > sock_set_flag(sk,= SOCK_DEAD) > > > > > > > > > > skb_queue_purge()= > > > > > > > > > > > > > > > > > > > > skb_queue_tail() > > > > > > > > > > > > > > > > > > > > [0]: > > > > > > > > > > > > > > > > > > > Fixes: f214f915e7db ("tcp: enable MSG_ZEROCOPY") > > > > > > > > > > Fixes: b5947e5d1e71 ("udp: msg_zerocopy") > > > > > > > > > > Reported-by: syzbot > > > > > > > > > > Signed-off-by: Kuniyuki Iwashima > > > > > > > > > > --- > > > > > > > > > > v2: > > > > > > > > > > * Move skb_queue_purge() after setting SOCK_DEAD in= udp_destroy_sock() > > > > > > > > > > * Check SOCK_DEAD in sock_queue_err_skb() with sk_e= rror_queue.lock > > > > > > > > > > * Add Fixes tag for TCP > > > > > > > > > > > > > > > > > > > > v1: https://lore.kernel.org/netdev/20230417171155.229= 16-1-kuniyu@amazon.com/ > > > > > > > > > > --- > > > > > > > > > > net/core/skbuff.c | 15 ++++++++++++--- > > > > > > > > > > net/ipv4/udp.c | 5 +++++ > > > > > > > > > > 2 files changed, 17 insertions(+), 3 deletions(-) > > > > > > > > > > > > > > > > > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > > > > > > > > index 4c0879798eb8..287b834df9c8 100644 > > > > > > > > > > --- a/net/core/skbuff.c > > > > > > > > > > +++ b/net/core/skbuff.c > > > > > > > > > > @@ -4979,6 +4979,8 @@ static void skb_set_err_queue(s= truct sk_buff *skb) > > > > > > > > > > */ > > > > > > > > > > int sock_queue_err_skb(struct sock *sk, struct sk_bu= ff *skb) > > > > > > > > > > { > > > > > > > > > > + unsigned long flags; > > > > > > > > > > + > > > > > > > > > > if (atomic_read(&sk->sk_rmem_alloc) + skb->tr= uesize >=3D > > > > > > > > > > (unsigned int)READ_ONCE(sk->sk_rcvbuf)) > > > > > > > > > > return -ENOMEM; > > > > > > > > > > @@ -4992,9 +4994,16 @@ int sock_queue_err_skb(struct = sock *sk, struct sk_buff *skb) > > > > > > > > > > /* before exiting rcu section, make sure dst = is refcounted */ > > > > > > > > > > skb_dst_force(skb); > > > > > > > > > > > > > > > > > > > > - skb_queue_tail(&sk->sk_error_queue, skb); > > > > > > > > > > - if (!sock_flag(sk, SOCK_DEAD)) > > > > > > > > > > - sk_error_report(sk); > > > > > > > > > > + spin_lock_irqsave(&sk->sk_error_queue.lock, f= lags); > > > > > > > > > > + if (sock_flag(sk, SOCK_DEAD)) { > > > > > > > > > > > > > > > > > > SOCK_DEAD is set without holding sk_error_queue.lock, s= o I wonder why you > > > > > > > > > want to add a confusing construct. > > > > > > > > > > > > > > > > > > Just bail early ? > > > > > > > > > > > > > > > > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > > > > > > > index ef81452759be3fd251faaf76d89cfd002ee79256..fda05cb= 44f95821e98f8c5c05fba840a9d276abb > > > > > > > > > 100644 > > > > > > > > > --- a/net/core/skbuff.c > > > > > > > > > +++ b/net/core/skbuff.c > > > > > > > > > @@ -4983,6 +4983,9 @@ int sock_queue_err_skb(struct soc= k *sk, struct > > > > > > > > > sk_buff *skb) > > > > > > > > > (unsigned int)READ_ONCE(sk->sk_rcvbuf)) > > > > > > > > > return -ENOMEM; > > > > > > > > > > > > > > > > > > + if (sock_flag(sk, SOCK_DEAD)) > > > > > > > > > + return -EINVAL; > > > > > > > > > + > > > > > > > > > > > > > > > > Isn't it possible that these sequences happen > > > > > > > > > > > > > > > > close() > > > > > > > > sock_set_flag(sk, SOCK_DEAD); > > > > > > > > skb_queue_purge(&sk->sk_error_queue) > > > > > > > > > > > > > > > > between the skb_queue_tail() below ? (2nd race mentioned = in changelog) > > > > > > > > > > > > > > > > I thought we can guarantee the ordering by taking the sam= e lock. > > > > > > > > > > > > > > > > > > > > > > This is fragile. > > > > > > > > > > > > Yes, but I didn't have better idea to avoid the race... > > > > > > > > > > > > > > > > > > > > We could very well rewrite skb_queue_purge() to not acquire= the lock > > > > > > > in the common case. > > > > > > > I had the following in my tree for a while, to avoid many a= tomic and > > > > > > > irq masking operations... > > > > > > > > > > > > Cool, and it still works with my patch, no ? > > > > > > > > > > > = > > > > > = > > > > > Really the only thing that ensures a race is not possible is th= e > > > > > typical sk_refcnt acquisition. > > > > > = > > > > > But I do not see why an skb stored in error_queue should keep t= he > > > > > refcnt on the socket. > > > > > This seems like a chicken and egg problem, and caused various i= ssues > > > > > in the past, > > > > > see for instance [1] > > > > > = > > > > > We better make sure error queue is purged at socket dismantle (= after > > > > > refcnt reached 0) > > > > = > > > > The problem here is that the timestamp queued on the error queue > > > > holds a reference on a ubuf if MSG_ZEROCOPY and that ubuf holds a= n > > > > sk_ref. > > > > = > > > > The timestamped packet may contain packet contents, so the ubuf > > > > ref is not superfluous. > > > > = > > > > Come to think of it, we've always maintained that zerocopy packet= s > > > > should not be looped to sockets where they can be queued indefini= tely, > > > > including packet sockets. > > > > = > > > > If we enforce that for these tx timestamps too, then that also > > > > solves this issue. > > > > = > > > > A process that wants efficient MSG_ZEROCOPY will have to request > > > > timestamping with SOF_TIMESTAMPING_OPT_TSONLY to avoid returning = the > > > > data along with the timestamp. > > > = > > > Actually, my first attempt was similar to this that avoids skb_clon= e() > > > silently if MSG_ZEROCOPY, but this kind of way could break users wh= o > > > were using tstamp and just added MSG_ZEROCOPY logic to their app, s= o > > > I placed skb_queue_purge() during close(). > > > = > > > ---8<--- > > > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > > > index eb7d33b41e71..9318b438888e 100644 > > > --- a/net/core/skbuff.c > > > +++ b/net/core/skbuff.c > > > @@ -5135,7 +5149,7 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb= , > > > if (!skb_may_tx_timestamp(sk, tsonly)) > > > return; > > > = > > > - if (tsonly) { > > > + if (tsonly || skb_zcopy(orig_skb)) { > > > #ifdef CONFIG_INET > > > if ((sk->sk_tsflags & SOF_TIMESTAMPING_OPT_STATS) && > > > sk_is_tcp(sk)) { > > > ---8<--- > > = > > Actually, the skb_clone in __skb_tstamp_tx should already release > > the reference on the ubuf. > > = > > With the same mechanism that we rely on for packet sockets, e.g., > > in dev_queue_xmit_nit. > > = > > skb_clone calls skb_orphan_frags calls skb_copy_ubufs for zerocopy > > skbs. Which creates a copy of the data and calls skb_zcopy_clear. > > = > > The skb that gets queued onto the error queue should not have a > > reference on an ubuf: skb_zcopy(skb) should return NULL. > = > Exactly, so how about this ? > = > ---8<--- > diff --git a/net/core/skbuff.c b/net/core/skbuff.c > index 768f9d04911f..0fa0b2ac7071 100644 > --- a/net/core/skbuff.c > +++ b/net/core/skbuff.c > @@ -5166,6 +5166,9 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, > if (!skb) > return; > = > + if (skb_zcopy(skb) && skb_copy_ubufs(skb, GFP_ATOMIC)) > + return; > + > if (tsonly) { > skb_shinfo(skb)->tx_flags |=3D skb_shinfo(orig_skb)->tx_flags & > SKBTX_ANY_TSTAMP; > ---8<--- > = What I meant was that given this I don't understand how a packet with ubuf references gets queued at all. __skb_tstamp_tx does not queue orig_skb. It either allocates a new skb or calls skb =3D skb_clone(orig_skb). That existing call internally calls skb_orphan_frags and skb_copy_ubufs. So the extra test should not be needed. Indeed I would be surprised if this triggers: @@ -5164,6 +5164,8 @@ void __skb_tstamp_tx(struct sk_buff *orig_skb, if (!skb) return; = + WARN_ON_ONCE(skb_zcopy(sbk)); + if (tsonly) { skb_shinfo(skb)->tx_flags |=3D skb_shinfo(orig_skb)->tx_f= lags & SKBTX_ANY_TSTAMP;