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

Kuniyuki Iwashima
2025-09-25T19:51:48Z

On Thu, Sep 25, 2025 at 12:37 PM Eric Dumazet <edumazet@google.com> wrote:
>
> On Thu, Sep 25, 2025 at 12:25 PM Kuniyuki Iwashima <kuniyu@google.com> wrote:
> >
> > 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.
> >
>
> I definitely vote to remove INET_PROTOSW_ICSK from smc.
>
> We want to reserve inet_connection_sock to TCP only, so that we can
> move fields to better
> cache friendly locations in tcp_sock hopefully for linux-6.19

Fully agreed.

Wang: please squash the revert of 6fd27ea183c2 for
INET_PROTOSW_ICSK removal. This is for one of
IS_ICSK branches.