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

Kuniyuki Iwashima
2025-09-25T18:46:40Z

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 ?

> >
> > Reported-by: syzbot+f775be4458668f7d220e@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=f775be4458668f7d220e
> > Tested-by: syzbot+f775be4458668f7d220e@syzkaller.appspotmail.com
> > Fixes: d25a92ccae6b ("net/smc: Introduce IPPROTO_SMC")
> > Signed-off-by: Wang Liang <wangliang74@huawei.com>
> > ---
> > net/smc/smc.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/smc/smc.h b/net/smc/smc.h
> > index 2c9084963739..1b20f0c927d3 100644
> > --- a/net/smc/smc.h
> > +++ b/net/smc/smc.h
> > @@ -285,7 +285,7 @@ struct smc_connection {
> > struct smc_sock { /* smc sock container */
> > union {
> > struct sock sk;
> > - struct inet_sock icsk_inet;
> > + struct inet_connection_sock inet_conn;
> > };
> > struct socket *clcsock; /* internal tcp socket */
> > void (*clcsk_state_change)(struct sock *sk);
> > --
> > 2.34.1
> >
>
> Kuniyuki, can you please review, I think you had a related fix recently.
>
> Thanks.
>
> commit 60ada4fe644edaa6c2da97364184b0425e8aeaf5
> Author: Kuniyuki Iwashima <kuniyu@google.com>
> Date: Fri Jul 11 06:07:52 2025 +0000
>
> smc: Fix various oops due to inet_sock type confusion.