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Message-ID: <CANn89i+V847kRTTFW43ouZXXuaBs177fKv5_bqfbvRutpg+s6g@mail.gmail.com>
Date: Thu, 25 Sep 2025 11:53:56 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: Kuniyuki Iwashima <kuniyu@...gle.com>
Cc: Wang Liang <wangliang74@...wei.com>, alibuda@...ux.alibaba.com,
dust.li@...ux.alibaba.com, sidraya@...ux.ibm.com, wenjia@...ux.ibm.com,
mjambigi@...ux.ibm.com, tonylu@...ux.alibaba.com, guwen@...ux.alibaba.com,
davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
yuehaibing@...wei.com, zhangchangzhong@...wei.com,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
linux-rdma@...r.kernel.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH net] net/smc: fix general protection fault in __smc_diag_dump
On Thu, Sep 25, 2025 at 11:46 AM Kuniyuki Iwashima <kuniyu@...gle.com> wrote:
>
> Thanks Eric for CCing me.
>
> On Thu, Sep 25, 2025 at 7:32 AM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Mon, Sep 22, 2025 at 4:57 AM Wang Liang <wangliang74@...wei.com> wrote:
> > >
> > > The syzbot report a crash:
> > >
> > > Oops: general protection fault, probably for non-canonical address 0xfbd5a5d5a0000003: 0000 [#1] SMP KASAN NOPTI
> > > KASAN: maybe wild-memory-access in range [0xdead4ead00000018-0xdead4ead0000001f]
> > > CPU: 1 UID: 0 PID: 6949 Comm: syz.0.335 Not tainted syzkaller #0 PREEMPT(full)
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
> > > RIP: 0010:smc_diag_msg_common_fill net/smc/smc_diag.c:44 [inline]
> > > RIP: 0010:__smc_diag_dump.constprop.0+0x3ca/0x2550 net/smc/smc_diag.c:89
> > > Call Trace:
> > > <TASK>
> > > smc_diag_dump_proto+0x26d/0x420 net/smc/smc_diag.c:217
> > > smc_diag_dump+0x27/0x90 net/smc/smc_diag.c:234
> > > netlink_dump+0x539/0xd30 net/netlink/af_netlink.c:2327
> > > __netlink_dump_start+0x6d6/0x990 net/netlink/af_netlink.c:2442
> > > netlink_dump_start include/linux/netlink.h:341 [inline]
> > > smc_diag_handler_dump+0x1f9/0x240 net/smc/smc_diag.c:251
> > > __sock_diag_cmd net/core/sock_diag.c:249 [inline]
> > > sock_diag_rcv_msg+0x438/0x790 net/core/sock_diag.c:285
> > > netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
> > > netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
> > > netlink_unicast+0x5a7/0x870 net/netlink/af_netlink.c:1346
> > > netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
> > > sock_sendmsg_nosec net/socket.c:714 [inline]
> > > __sock_sendmsg net/socket.c:729 [inline]
> > > ____sys_sendmsg+0xa95/0xc70 net/socket.c:2614
> > > ___sys_sendmsg+0x134/0x1d0 net/socket.c:2668
> > > __sys_sendmsg+0x16d/0x220 net/socket.c:2700
> > > do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> > > do_syscall_64+0xcd/0x4e0 arch/x86/entry/syscall_64.c:94
> > > entry_SYSCALL_64_after_hwframe+0x77/0x7f
> > > </TASK>
> > >
> > > The process like this:
> > >
> > > (CPU1) | (CPU2)
> > > ---------------------------------|-------------------------------
> > > inet_create() |
> > > // init clcsock to NULL |
> > > sk = sk_alloc() |
> > > |
> > > // unexpectedly change clcsock |
> > > inet_init_csk_locks() |
> > > |
> > > // add sk to hash table |
> > > smc_inet_init_sock() |
> > > smc_sk_init() |
> > > smc_hash_sk() |
> > > | // traverse the hash table
> > > | smc_diag_dump_proto
> > > | __smc_diag_dump()
> > > | // visit wrong clcsock
> > > | smc_diag_msg_common_fill()
> > > // alloc clcsock |
> > > smc_create_clcsk |
> > > sock_create_kern |
> > >
> > > With CONFIG_DEBUG_LOCK_ALLOC=y, the smc->clcsock is unexpectedly changed
> > > in inet_init_csk_locks(), because the struct smc_sock does not have struct
> > > inet_connection_sock as the first member.
> > >
> > > Previous commit 60ada4fe644e ("smc: Fix various oops due to inet_sock type
> > > confusion.") add inet_sock as the first member of smc_sock. For protocol
> > > with INET_PROTOSW_ICSK, use inet_connection_sock instead of inet_sock is
> > > more appropriate.
>
> Why is INET_PROTOSW_ICSK necessary in the first place ?
>
> I don't see a clear reason because smc_clcsock_accept() allocates
> a new sock by smc_sock_alloc() and does not use inet_accept().
>
> Or is there any other path where smc_sock is cast to
> inet_connection_sock ?
What I saw in this code was a missing protection.
smc_diag_msg_common_fill() runs without socket lock being held.
I was thinking of this fix, but apparently syzbot still got crashes.
diff --git a/net/smc/smc_close.c b/net/smc/smc_close.c
index 10219f55aad14d795dabe4331458bd1b73c22789..b6abd0efea22c0c9726090b5de60e648b86e09a0
100644
--- a/net/smc/smc_close.c
+++ b/net/smc/smc_close.c
@@ -30,7 +30,8 @@ void smc_clcsock_release(struct smc_sock *smc)
mutex_lock(&smc->clcsock_release_lock);
if (smc->clcsock) {
tcp = smc->clcsock;
- smc->clcsock = NULL;
+ WRITE_ONCE(smc->clcsock, NULL);
+ synchronize_rcu();
sock_release(tcp);
}
mutex_unlock(&smc->clcsock_release_lock);
diff --git a/net/smc/smc_diag.c b/net/smc/smc_diag.c
index bf0beaa23bdb63edfe0c37515aa17a04bb648c08..069607c1db9aff76d1d4f23b47dfeb5177c433d8
100644
--- a/net/smc/smc_diag.c
+++ b/net/smc/smc_diag.c
@@ -35,26 +35,32 @@ static struct smc_diag_dump_ctx
*smc_dump_context(struct netlink_callback *cb)
static void smc_diag_msg_common_fill(struct smc_diag_msg *r, struct sock *sk)
{
struct smc_sock *smc = smc_sk(sk);
+ struct socket *clcsock;
memset(r, 0, sizeof(*r));
r->diag_family = sk->sk_family;
sock_diag_save_cookie(sk, r->id.idiag_cookie);
- if (!smc->clcsock)
- return;
- r->id.idiag_sport = htons(smc->clcsock->sk->sk_num);
- r->id.idiag_dport = smc->clcsock->sk->sk_dport;
- r->id.idiag_if = smc->clcsock->sk->sk_bound_dev_if;
+
+ rcu_read_lock();
+ clcsock = READ_ONCE(smc->clcsock);
+ if (!clcsock)
+ goto unlock;
+ r->id.idiag_sport = htons(clcsock->sk->sk_num);
+ r->id.idiag_dport = clcsock->sk->sk_dport;
+ r->id.idiag_if = clcsock->sk->sk_bound_dev_if;
if (sk->sk_protocol == SMCPROTO_SMC) {
- r->id.idiag_src[0] = smc->clcsock->sk->sk_rcv_saddr;
- r->id.idiag_dst[0] = smc->clcsock->sk->sk_daddr;
+ r->id.idiag_src[0] = clcsock->sk->sk_rcv_saddr;
+ r->id.idiag_dst[0] = clcsock->sk->sk_daddr;
#if IS_ENABLED(CONFIG_IPV6)
} else if (sk->sk_protocol == SMCPROTO_SMC6) {
- memcpy(&r->id.idiag_src, &smc->clcsock->sk->sk_v6_rcv_saddr,
- sizeof(smc->clcsock->sk->sk_v6_rcv_saddr));
- memcpy(&r->id.idiag_dst, &smc->clcsock->sk->sk_v6_daddr,
- sizeof(smc->clcsock->sk->sk_v6_daddr));
+ memcpy(&r->id.idiag_src, &clcsock->sk->sk_v6_rcv_saddr,
+ sizeof(clcsock->sk->sk_v6_rcv_saddr));
+ memcpy(&r->id.idiag_dst, &clcsock->sk->sk_v6_daddr,
+ sizeof(clcsock->sk->sk_v6_daddr));
#endif
}
+unlock:
+ rcu_read_unlock();
}
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