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Message-ID: <CAAVpQUAGbadNDhtn=vdwQHXc51vOA_22vH-SYyyi=ANhoS=ROQ@mail.gmail.com>
Date: Thu, 11 Sep 2025 09:57:15 -0700
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org,
"D. Wythe" <alibuda@...ux.alibaba.com>, Dust Li <dust.li@...ux.alibaba.com>,
Sidraya Jayagond <sidraya@...ux.ibm.com>, Wenjia Zhang <wenjia@...ux.ibm.com>,
Mahanta Jambigi <mjambigi@...ux.ibm.com>, Tony Lu <tonylu@...ux.alibaba.com>,
Wen Gu <guwen@...ux.alibaba.com>, Ursula Braun <ubraun@...ux.vnet.ibm.com>
Subject: Re: [PATCH v1 net 3/8] smc: Use sk_dst_dev_rcu() in in smc_clc_prfx_set().
On Wed, Sep 10, 2025 at 11:28 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Wed, Sep 10, 2025 at 8:06 PM Kuniyuki Iwashima <kuniyu@...gle.com> wrote:
> >
> > smc_clc_prfx_set() is called during connect() and not under RCU
> > nor RTNL.
> >
> > Using sk_dst_get(sk)->dev could trigger UAF.
> >
> > Let's use sk_dst_get_rcu() under rcu_read_lock() after
> > kernel_getsockname().
> >
> > While at it, we change the 1st arg of smc_clc_prfx_set[46]_rcu()
> > not to touch dst there.
> >
> > Fixes: a046d57da19f ("smc: CLC handshake (incl. preparation steps)")
> > Signed-off-by: Kuniyuki Iwashima <kuniyu@...gle.com>
> > ---
> > Cc: "D. Wythe" <alibuda@...ux.alibaba.com>
> > Cc: Dust Li <dust.li@...ux.alibaba.com>
> > Cc: Sidraya Jayagond <sidraya@...ux.ibm.com>
> > Cc: Wenjia Zhang <wenjia@...ux.ibm.com>
> > Cc: Mahanta Jambigi <mjambigi@...ux.ibm.com>
> > Cc: Tony Lu <tonylu@...ux.alibaba.com>
> > Cc: Wen Gu <guwen@...ux.alibaba.com>
> > Cc: Ursula Braun <ubraun@...ux.vnet.ibm.com>
> > ---
> > net/smc/smc_clc.c | 39 ++++++++++++++++++++-------------------
> > 1 file changed, 20 insertions(+), 19 deletions(-)
> >
> > diff --git a/net/smc/smc_clc.c b/net/smc/smc_clc.c
> > index 08be56dfb3f2..9aa1d75d3079 100644
> > --- a/net/smc/smc_clc.c
> > +++ b/net/smc/smc_clc.c
> > @@ -509,10 +509,10 @@ static bool smc_clc_msg_hdr_valid(struct smc_clc_msg_hdr *clcm, bool check_trl)
> > }
> >
> > /* find ipv4 addr on device and get the prefix len, fill CLC proposal msg */
> > -static int smc_clc_prfx_set4_rcu(struct dst_entry *dst, __be32 ipv4,
> > +static int smc_clc_prfx_set4_rcu(struct net_device *dev, __be32 ipv4,
> > struct smc_clc_msg_proposal_prefix *prop)
> > {
> > - struct in_device *in_dev = __in_dev_get_rcu(dst->dev);
> > + struct in_device *in_dev = __in_dev_get_rcu(dev);
> > const struct in_ifaddr *ifa;
> >
> > if (!in_dev)
> > @@ -530,12 +530,12 @@ static int smc_clc_prfx_set4_rcu(struct dst_entry *dst, __be32 ipv4,
> > }
> >
> > /* fill CLC proposal msg with ipv6 prefixes from device */
> > -static int smc_clc_prfx_set6_rcu(struct dst_entry *dst,
> > +static int smc_clc_prfx_set6_rcu(struct net_device *dev,
> > struct smc_clc_msg_proposal_prefix *prop,
> > struct smc_clc_ipv6_prefix *ipv6_prfx)
> > {
> > #if IS_ENABLED(CONFIG_IPV6)
> > - struct inet6_dev *in6_dev = __in6_dev_get(dst->dev);
> > + struct inet6_dev *in6_dev = __in6_dev_get(dev);
> > struct inet6_ifaddr *ifa;
> > int cnt = 0;
> >
> > @@ -564,41 +564,42 @@ static int smc_clc_prfx_set(struct socket *clcsock,
> > struct smc_clc_msg_proposal_prefix *prop,
> > struct smc_clc_ipv6_prefix *ipv6_prfx)
> > {
> > - struct dst_entry *dst = sk_dst_get(clcsock->sk);
> > struct sockaddr_storage addrs;
> > struct sockaddr_in6 *addr6;
> > struct sockaddr_in *addr;
> > + struct net_device *dev;
> > int rc = -ENOENT;
> >
> > - if (!dst) {
> > - rc = -ENOTCONN;
> > - goto out;
> > - }
> > - if (!dst->dev) {
> > - rc = -ENODEV;
> > - goto out_rel;
> > - }
> > /* get address to which the internal TCP socket is bound */
> > if (kernel_getsockname(clcsock, (struct sockaddr *)&addrs) < 0)
> > - goto out_rel;
> > + goto out;
> > +
> > /* analyze IP specific data of net_device belonging to TCP socket */
> > addr6 = (struct sockaddr_in6 *)&addrs;
> > +
> > rcu_read_lock();
> > +
> > + dev = sk_dst_dev_rcu(clcsock->sk);
> > + if (!dev) {
> > + rc = -ENODEV;
> > + goto out_unlock;
> > + }
> > +
> > if (addrs.ss_family == PF_INET) {
> > /* IPv4 */
> > addr = (struct sockaddr_in *)&addrs;
> > - rc = smc_clc_prfx_set4_rcu(dst, addr->sin_addr.s_addr, prop);
> > + rc = smc_clc_prfx_set4_rcu(dev, addr->sin_addr.s_addr, prop);
> > } else if (ipv6_addr_v4mapped(&addr6->sin6_addr)) {
> > /* mapped IPv4 address - peer is IPv4 only */
> > - rc = smc_clc_prfx_set4_rcu(dst, addr6->sin6_addr.s6_addr32[3],
> > + rc = smc_clc_prfx_set4_rcu(dev, addr6->sin6_addr.s6_addr32[3],
> > prop);
> > } else {
> > /* IPv6 */
> > - rc = smc_clc_prfx_set6_rcu(dst, prop, ipv6_prfx);
> > + rc = smc_clc_prfx_set6_rcu(dev, prop, ipv6_prfx);
> > }
> > +
> > +out_unlock:
> > rcu_read_unlock();
> > -out_rel:
> > - dst_release(dst);
> > out:
> > return rc;
> > }
> > --
> > 2.51.0.384.g4c02a37b29-goog
> >
>
> Same comment, I had a patch to fix this without a new helper.
>
> We have hundreds of dst->dev places to fix, very few sk_dst_get().
>
> This is why I think sk_dst_dev_rcu() is not necessary.
I added helpers for new users not to read sk_dst_get()->dst
directly, but the point is fair. Maybe we can convert all users
to __sk_dst_get() or remove rcu_read_lock() in sk_dst_get().
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