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[34.150.157.240]) by smtp.gmail.com with ESMTPSA id 70-20020a370649000000b0074df1d74841sm1097804qkg.72.2023.04.17.14.53.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 14:53:33 -0700 (PDT) Date: Mon, 17 Apr 2023 17:53:33 -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: <643dbfdd431ac_2d6665294a0@willemb.c.googlers.com.notmuch> In-Reply-To: <20230417212658.51343-1-kuniyu@amazon.com> References: <643dadc434cac_2d31fb2945@willemb.c.googlers.com.notmuch> <20230417212658.51343-1-kuniyu@amazon.com> Subject: RE: [PATCH v1 net] 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: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Kuniyuki Iwashima wrote: > From: Willem de Bruijn > Date: Mon, 17 Apr 2023 16:36:20 -0400 > > Kuniyuki Iwashima wrote: > > > syzkaller reported [0] memory leaks of an UDP socket and ZEROCOPY > > > skbs. We can reproduce the problem with these sequences: > > > > > > sk = socket(AF_INET, SOCK_DGRAM, 0) > > > sk.setsockopt(SOL_SOCKET, SO_TIMESTAMPING, SOF_TIMESTAMPING_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(). Here, struct > > > ubuf_info_msgzc indirectly holds a refcnt of the socket. 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_ubufs() calls > > > skb_unclone(), and pskb_expand_head() increments skb->cb->ubuf.refcnt. > > > This additional count is decremented while freeing the 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 the 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 call skb_queue_purge() while we close() > > > UDP sockets. > > > > > > Note that TCP does not have this problem because skb_queue_purge() is > > > called by sk_stream_kill_queues() during close(). > > > > Thanks for the clear description. > > > > So the issue is that the tx timestamp notification is still queued on > > the error queue and this is not freed on socket destruction. > > > > That surprises me. The error definitely needs to be purged on socket > > destruction. And it is, called in inet_sock_destruct, which is called > > udp_destruct_sock. > > > > The issue here is that there is a circular dependency, where the > > sk_destruct is not called until the ref count drops to zero? > > Yes, right. > > > > > sk_stream_kill_queues is called from inet_csk_destroy_sock, from > > __tcp_close (and thus tcp_prot.close) among others. > > > > purging the error queue for other sockets on .close rather than > > .destroy sounds good to me. > > > > But SOF_TIMESTAMPING_TX_SOFTWARE and MSG_ZEROCOPY are not limited to > > TCP and UDP. So we probably need this in a more protocol independent > > close. > > At least, we limit SO_ZEROCOPY to TCP, UDP and RDS for now. Also, RDS > seems to just use TCP. [0] > > ---8<--- > case SO_ZEROCOPY: > if (sk->sk_family == PF_INET || sk->sk_family == PF_INET6) { > if (!(sk_is_tcp(sk) || > (sk->sk_type == SOCK_DGRAM && > sk->sk_protocol == IPPROTO_UDP))) > ret = -EOPNOTSUPP; > } else if (sk->sk_family != PF_RDS) { > ret = -EOPNOTSUPP; > } > if (!ret) { > if (val < 0 || val > 1) > ret = -EINVAL; > else > sock_valbool_flag(sk, SOCK_ZEROCOPY, valbool); > } > break; > ---8<--- > > [0]: https://lore.kernel.org/netdev/cover.1518718761.git.sowmini.varadhan@oracle.com/ Good point, thanks. I used to experiment with more protocols, as can be seen from msg_zerocopy.c. But those are thankfully not relevant. > > Thanks, > Kuniyuki > > > > > > > [0]: > > > BUG: memory leak > > > unreferenced object 0xffff88800c6d2d00 (size 1152): > > > comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s) > > > hex dump (first 32 bytes): > > > 00 00 00 00 00 00 00 00 cd af e8 81 00 00 00 00 ................ > > > 02 00 07 40 00 00 00 00 00 00 00 00 00 00 00 00 ...@............ > > > backtrace: > > > [<0000000055636812>] sk_prot_alloc+0x64/0x2a0 net/core/sock.c:2024 > > > [<0000000054d77b7a>] sk_alloc+0x3b/0x800 net/core/sock.c:2083 > > > [<0000000066f3c7e0>] inet_create net/ipv4/af_inet.c:319 [inline] > > > [<0000000066f3c7e0>] inet_create+0x31e/0xe40 net/ipv4/af_inet.c:245 > > > [<000000009b83af97>] __sock_create+0x2ab/0x550 net/socket.c:1515 > > > [<00000000b9b11231>] sock_create net/socket.c:1566 [inline] > > > [<00000000b9b11231>] __sys_socket_create net/socket.c:1603 [inline] > > > [<00000000b9b11231>] __sys_socket_create net/socket.c:1588 [inline] > > > [<00000000b9b11231>] __sys_socket+0x138/0x250 net/socket.c:1636 > > > [<000000004fb45142>] __do_sys_socket net/socket.c:1649 [inline] > > > [<000000004fb45142>] __se_sys_socket net/socket.c:1647 [inline] > > > [<000000004fb45142>] __x64_sys_socket+0x73/0xb0 net/socket.c:1647 > > > [<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > [<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 > > > [<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > BUG: memory leak > > > unreferenced object 0xffff888017633a00 (size 240): > > > comm "syz-executor392", pid 264, jiffies 4294785440 (age 13.044s) > > > hex dump (first 32 bytes): > > > 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ > > > 00 00 00 00 00 00 00 00 00 2d 6d 0c 80 88 ff ff .........-m..... > > > backtrace: > > > [<000000002b1c4368>] __alloc_skb+0x229/0x320 net/core/skbuff.c:497 > > > [<00000000143579a6>] alloc_skb include/linux/skbuff.h:1265 [inline] > > > [<00000000143579a6>] sock_omalloc+0xaa/0x190 net/core/sock.c:2596 > > > [<00000000be626478>] msg_zerocopy_alloc net/core/skbuff.c:1294 [inline] > > > [<00000000be626478>] msg_zerocopy_realloc+0x1ce/0x7f0 net/core/skbuff.c:1370 > > > [<00000000cbfc9870>] __ip_append_data+0x2adf/0x3b30 net/ipv4/ip_output.c:1037 > > > [<0000000089869146>] ip_make_skb+0x26c/0x2e0 net/ipv4/ip_output.c:1652 > > > [<00000000098015c2>] udp_sendmsg+0x1bac/0x2390 net/ipv4/udp.c:1253 > > > [<0000000045e0e95e>] inet_sendmsg+0x10a/0x150 net/ipv4/af_inet.c:819 > > > [<000000008d31bfde>] sock_sendmsg_nosec net/socket.c:714 [inline] > > > [<000000008d31bfde>] sock_sendmsg+0x141/0x190 net/socket.c:734 > > > [<0000000021e21aa4>] __sys_sendto+0x243/0x360 net/socket.c:2117 > > > [<00000000ac0af00c>] __do_sys_sendto net/socket.c:2129 [inline] > > > [<00000000ac0af00c>] __se_sys_sendto net/socket.c:2125 [inline] > > > [<00000000ac0af00c>] __x64_sys_sendto+0xe1/0x1c0 net/socket.c:2125 > > > [<0000000066999e0e>] do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > [<0000000066999e0e>] do_syscall_64+0x38/0x90 arch/x86/entry/common.c:80 > > > [<0000000017f238c1>] entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > Fixes: b5947e5d1e71 ("udp: msg_zerocopy") > > > Reported-by: syzbot > > > Signed-off-by: Kuniyuki Iwashima > > > --- > > > include/net/udp.h | 5 +++++ > > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/include/net/udp.h b/include/net/udp.h > > > index de4b528522bb..b9182f166b2f 100644 > > > --- a/include/net/udp.h > > > +++ b/include/net/udp.h > > > @@ -195,6 +195,11 @@ void udp_lib_rehash(struct sock *sk, u16 new_hash); > > > > > > static inline void udp_lib_close(struct sock *sk, long timeout) > > > { > > > + /* A zerocopy skb has a refcnt of sk and may be > > > + * put into sk_error_queue with TX timestamp > > > + */ > > > + skb_queue_purge(&sk->sk_error_queue); > > > + > > > sk_common_release(sk); > > > } Does this leave a race, where another completion may be queued between skb_queue_purge and the eventual sock_put in sk_common_release? Unfortunately even the sock_set_flag(sk, SOCK_DEAD) is not sufficient to ensure that no tx completions are subsequently queued for packets that are in transmission. sk_common_release has a comment * receive queue, but transmitted packets will delay socket destruction * until the last reference will be released. */ This should equally apply to TCP. Evidentlly it is not a problem there. I don't entirely follow yet how this is avoided. MSG_ZEROCOPY notifications are not queued if SOCK_DEAD (first branch in __msg_zerocopy_callback). Perhaps we need the same in sock_queue_err_skb?