From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH -next v2] unix stream: Fix use-after-free crashes Date: Thu, 08 Sep 2011 09:11:59 +0200 Message-ID: <1315465919.2532.19.camel@edumazet-laptop> References: <4E631032.6050606@intel.com> <1315326326.2576.2980.camel@schen9-DESK> <1315330805.2899.16.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC> <1315335019.2576.3048.camel@schen9-DESK> <1315335660.3400.7.camel@edumazet-laptop> <1315337580.2576.3066.camel@schen9-DESK> <1315338186.3400.20.camel@edumazet-laptop> <1315339157.2576.3079.camel@schen9-DESK> <1315340388.3400.28.camel@edumazet-laptop> <1315372100.3400.76.camel@edumazet-laptop> <4E66FF38.9000107@intel.com> <1315381503.3400.85.camel@edumazet-laptop> <1315396903.2364.23.camel@schen9-mobl> <1315406256.6287.7.camel@schen9-mobl> <4E680BF1.8000901@intel.com> <1315429583.2361.3.camel@schen9-mobl> <1315461572.2532.7.camel@edumazet-laptop> <4E685F19.6030407@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Tim Chen , "sedat.dilek@gmail.com" , "Yan, Zheng" , "netdev@vger.kernel.org" , "davem@davemloft.net" , "sfr@canb.auug.org.au" , "jirislaby@gmail.com" , "Shi, Alex" , Valdis Kletnieks To: "Yan, Zheng" Return-path: Received: from mail-ww0-f44.google.com ([74.125.82.44]:47995 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755856Ab1IHHMG (ORCPT ); Thu, 8 Sep 2011 03:12:06 -0400 Received: by wwf5 with SMTP id 5so528758wwf.1 for ; Thu, 08 Sep 2011 00:12:03 -0700 (PDT) In-Reply-To: <4E685F19.6030407@intel.com> Sender: netdev-owner@vger.kernel.org List-ID: Le jeudi 08 septembre 2011 =C3=A0 14:22 +0800, Yan, Zheng a =C3=A9crit = : > I don't think so. unix_scm_to_skb() calls unix_attach_fds(), it > always duplicates scm->fp.=20 What a mess. This code is a nightmare. Part of the mess comes from scm_destroy() and scm_release() duplication= =2E We should have scm_destroy() only, as before, and NULLify scm->pid/cred in unix_scm_to_skb() when we steal references. It makes more sense and keeps things clearer. include/net/scm.h | 9 --------- net/unix/af_unix.c | 27 +++++++++++++++------------ 2 files changed, 15 insertions(+), 21 deletions(-) diff --git a/include/net/scm.h b/include/net/scm.h index 68e1e48..2a5b42f 100644 --- a/include/net/scm.h +++ b/include/net/scm.h @@ -78,15 +78,6 @@ static __inline__ void scm_destroy(struct scm_cookie= *scm) __scm_destroy(scm); } =20 -static __inline__ void scm_release(struct scm_cookie *scm) -{ - /* keep ref on pid and cred */ - scm->pid =3D NULL; - scm->cred =3D NULL; - if (scm->fp) - __scm_destroy(scm); -} - static __inline__ int scm_send(struct socket *sock, struct msghdr *msg= , struct scm_cookie *scm) { diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index e6d9d10..1fa270a 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1379,15 +1379,18 @@ static int unix_attach_fds(struct scm_cookie *s= cm, struct sk_buff *skb) } =20 static int unix_scm_to_skb(struct scm_cookie *scm, struct sk_buff *skb= , - bool send_fds, bool ref) + bool send_fds, bool steal_refs) { int err =3D 0; - if (ref) { + + if (!steal_refs) { UNIXCB(skb).pid =3D get_pid(scm->pid); UNIXCB(skb).cred =3D get_cred(scm->cred); } else { UNIXCB(skb).pid =3D scm->pid; UNIXCB(skb).cred =3D scm->cred; + scm->pid =3D NULL; + scm->cred =3D NULL; } UNIXCB(skb).fp =3D NULL; if (scm->fp && send_fds) @@ -1454,7 +1457,7 @@ static int unix_dgram_sendmsg(struct kiocb *kiocb= , struct socket *sock, if (skb =3D=3D NULL) goto out; =20 - err =3D unix_scm_to_skb(siocb->scm, skb, true, false); + err =3D unix_scm_to_skb(siocb->scm, skb, true, true); if (err < 0) goto out_free; max_level =3D err + 1; @@ -1550,7 +1553,7 @@ restart: unix_state_unlock(other); other->sk_data_ready(other, len); sock_put(other); - scm_release(siocb->scm); + scm_destroy(siocb->scm); return len; =20 out_unlock: @@ -1577,6 +1580,7 @@ static int unix_stream_sendmsg(struct kiocb *kioc= b, struct socket *sock, int sent =3D 0; struct scm_cookie tmp_scm; bool fds_sent =3D false; + bool steal_refs =3D false; int max_level; =20 if (NULL =3D=3D siocb->scm) @@ -1638,8 +1642,11 @@ static int unix_stream_sendmsg(struct kiocb *kio= cb, struct socket *sock, size =3D min_t(int, size, skb_tailroom(skb)); =20 =20 - /* Only send the fds and no ref to pid in the first buffer */ - err =3D unix_scm_to_skb(siocb->scm, skb, !fds_sent, fds_sent); + /* Only send the fds in first buffer + * Last buffer can steal our references to pid/cred + */ + steal_refs =3D (sent + size >=3D len); + err =3D unix_scm_to_skb(siocb->scm, skb, !fds_sent, steal_refs); if (err < 0) { kfree_skb(skb); goto out; @@ -1667,10 +1674,7 @@ static int unix_stream_sendmsg(struct kiocb *kio= cb, struct socket *sock, sent +=3D size; } =20 - if (skb) - scm_release(siocb->scm); - else - scm_destroy(siocb->scm); + scm_destroy(siocb->scm); siocb->scm =3D NULL; =20 return sent; @@ -1683,8 +1687,7 @@ pipe_err: send_sig(SIGPIPE, current, 0); err =3D -EPIPE; out_err: - if (skb =3D=3D NULL) - scm_destroy(siocb->scm); + scm_destroy(siocb->scm); out: siocb->scm =3D NULL; return sent ? : err;