Re: [PATCH net] net/smc: fix general protection fault in __smc_diag_dump

Kuniyuki Iwashima
2025-09-25T19:25:57Z

On Thu, Sep 25, 2025 at 11:54 AM Eric Dumazet <edumazet@google.com> wrote:
>
> On Thu, Sep 25, 2025 at 11:46 AM Kuniyuki Iwashima <kuniyu@google.com> wrote:
> >
> > Thanks Eric for CCing me.
> >
> > On Thu, Sep 25, 2025 at 7:32 AM Eric Dumazet <edumazet@google.com> wrote:
> > >
> > > On Mon, Sep 22, 2025 at 4:57 AM Wang Liang <wangliang74@huawei.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.

Looking at the test result,

https://syzkaller.appspot.com/x/report.txt?x=15944c7c580000
KASAN: maybe wild-memory-access in range [0xdead4ead00000018-0xdead4ead0000001f]

the top half of the address is SPINLOCK_MAGIC (0xdead4ead),
so the type confusion mentioned in the commit message makes
sense to me.

$ pahole -C inet_connection_sock vmlinux
struct inet_connection_sock {
...
struct request_sock_queue icsk_accept_queue; /* 992 80 */

$ pahole -C smc_sock vmlinux
struct smc_sock {
...
struct socket * clcsock; /* 992 8 */

The option is 1) let inet_init_csk_locks() init inet_connection_sock
or 2) avoid inet_init_csk_locks(), and I guess 2) could be better to
avoid potential issues in IS_ICSK branches.

>
> 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();
> }