Re: [PATCH mptcp-net] mptcp: pm: only set fullmesh for subflow endp

[Paolo Abeni <pabeni@redhat.com>]

On 1/16/25 7:15 PM, Matthieu Baerts (NGI0) wrote:
> With the in-kernel path-manager, it is possible to change the 'fullmesh'
> flag. The code in mptcp_pm_nl_fullmesh() expects to change it only on
> 'subflow' endpoints, to recreate more or less subflows using the linked
> address.
> 
> Unfortunately, the set_flags() hook was a bit more permissive, and
> allowed 'implicit' endpoints to get the 'fullmesh' flag while it is not
> allowed before.
> 
> That's what syzbot found, triggering the following warning:
> 
>   WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 __mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline]
>   WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline]
>   WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline]
>   WARNING: CPU: 0 PID: 6499 at net/mptcp/pm_netlink.c:1496 mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064
>   Modules linked in:
>   CPU: 0 UID: 0 PID: 6499 Comm: syz.1.413 Not tainted 6.13.0-rc5-syzkaller-00172-gd1bf27c4e176 #0
>   Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
>   RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_netlink.c:1496 [inline]
>   RIP: 0010:mptcp_pm_nl_fullmesh net/mptcp/pm_netlink.c:1980 [inline]
>   RIP: 0010:mptcp_nl_set_flags net/mptcp/pm_netlink.c:2003 [inline]
>   RIP: 0010:mptcp_pm_nl_set_flags+0x974/0xdc0 net/mptcp/pm_netlink.c:2064
>   Code: 01 00 00 49 89 c5 e8 fb 45 e8 f5 e9 b8 fc ff ff e8 f1 45 e8 f5 4c 89 f7 be 03 00 00 00 e8 44 1d 0b f9 eb a0 e8 dd 45 e8 f5 90 <0f> 0b 90 e9 17 ff ff ff 89 d9 80 e1 07 38 c1 0f 8c c9 fc ff ff 48
>   RSP: 0018:ffffc9000d307240 EFLAGS: 00010293
>   RAX: ffffffff8bb72e03 RBX: 0000000000000000 RCX: ffff88807da88000
>   RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
>   RBP: ffffc9000d307430 R08: ffffffff8bb72cf0 R09: 1ffff1100b842a5e
>   R10: dffffc0000000000 R11: ffffed100b842a5f R12: ffff88801e2e5ac0
>   R13: ffff88805c214800 R14: ffff88805c2152e8 R15: 1ffff1100b842a5d
>   FS:  00005555619f6500(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
>   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>   CR2: 0000000020002840 CR3: 00000000247e6000 CR4: 00000000003526f0
>   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>   Call Trace:
>    <TASK>
>    genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline]
>    genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
>    genl_rcv_msg+0xb14/0xec0 net/netlink/genetlink.c:1210
>    netlink_rcv_skb+0x1e3/0x430 net/netlink/af_netlink.c:2542
>    genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219
>    netlink_unicast_kernel net/netlink/af_netlink.c:1321 [inline]
>    netlink_unicast+0x7f6/0x990 net/netlink/af_netlink.c:1347
>    netlink_sendmsg+0x8e4/0xcb0 net/netlink/af_netlink.c:1891
>    sock_sendmsg_nosec net/socket.c:711 [inline]
>    __sock_sendmsg+0x221/0x270 net/socket.c:726
>    ____sys_sendmsg+0x52a/0x7e0 net/socket.c:2583
>    ___sys_sendmsg net/socket.c:2637 [inline]
>    __sys_sendmsg+0x269/0x350 net/socket.c:2669
>    do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>    do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>    entry_SYSCALL_64_after_hwframe+0x77/0x7f
>   RIP: 0033:0x7f5fe8785d29
>   Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
>   RSP: 002b:00007fff571f5558 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>   RAX: ffffffffffffffda RBX: 00007f5fe8975fa0 RCX: 00007f5fe8785d29
>   RDX: 0000000000000000 RSI: 0000000020000480 RDI: 0000000000000007
>   RBP: 00007f5fe8801b08 R08: 0000000000000000 R09: 0000000000000000
>   R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>   R13: 00007f5fe8975fa0 R14: 00007f5fe8975fa0 R15: 00000000000011f4
>    </TASK>
> 
> Here, syzbot managed to set the 'fullmesh' flag on an 'implicit' and
> used -- according to 'id_avail_bitmap' -- endpoint, causing the PM to
> try decrement the local_addr_used counter which is only incremented for
> the 'subflow' endpoint.
> 
> Note that 'no type' endpoints -- not 'subflow', 'signal', 'implicit' --
> are fine, because their ID will not be marked as used in the 'id_avail'
> bitmap, and setting 'fullmesh' can help forcing the creation of subflow
> when receiving an ADD_ADDR.
> 
> Fixes: 73c762c1f07d ("mptcp: set fullmesh flag in pm_netlink")
> Reported-by: syzbot+cd16e79c1e45f3fe0377@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/6786ac51.050a0220.216c54.00a6.GAE@google.com
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/540
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
>  net/mptcp/pm_netlink.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
> index fef01692eaed404e272359df691264f797240d10..7131dc2f312d923a31bb4b0460b6b4663376fbd0 100644
> --- a/net/mptcp/pm_netlink.c
> +++ b/net/mptcp/pm_netlink.c
> @@ -1986,7 +1986,8 @@ int mptcp_pm_nl_set_flags(struct mptcp_pm_addr_entry *local,
>  		return -EINVAL;
>  	}
>  	if ((local->flags & MPTCP_PM_ADDR_FLAG_FULLMESH) &&
> -	    (entry->flags & MPTCP_PM_ADDR_FLAG_SIGNAL)) {
> +	    ((entry->flags & MPTCP_PM_ADDR_FLAG_SIGNAL) ||
> +	     (entry->flags & MPTCP_PM_ADDR_FLAG_IMPLICIT))) {
>  		spin_unlock_bh(&pernet->lock);
>  		NL_SET_ERR_MSG_ATTR(info->extack, attr, "invalid addr flags");
>  		return -EINVAL;

LGTM, thanks!

slight preference for:

		entry->flags & (MPTCP_PM_ADDR_FLAG_SIGNAL ||
			        MPTCP_PM_ADDR_FLAG_IMPLICIT)

but definitely not strong opinion about it.

/P