Re: [PATCH 5.10 104/157] mptcp: put subflow sock on connect error

Naresh Kamboju
2021-03-24T08:33:19Z

On Mon, 22 Mar 2021 at 18:15, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> From: Florian Westphal <fw@strlen.de>
>
> [ Upstream commit f07157792c633b528de5fc1dbe2e4ea54f8e09d4 ]
>
> mptcp_add_pending_subflow() performs a sock_hold() on the subflow,
> then adds the subflow to the join list.
>
> Without a sock_put the subflow sk won't be freed in case connect() fails.
>
> unreferenced object 0xffff88810c03b100 (size 3000):
> [..]
> sk_prot_alloc.isra.0+0x2f/0x110
> sk_alloc+0x5d/0xc20
> inet6_create+0x2b7/0xd30
> __sock_create+0x17f/0x410
> mptcp_subflow_create_socket+0xff/0x9c0
> __mptcp_subflow_connect+0x1da/0xaf0
> mptcp_pm_nl_work+0x6e0/0x1120
> mptcp_worker+0x508/0x9a0
>
> Fixes: 5b950ff4331ddda ("mptcp: link MPC subflow into msk only after accept")
> Signed-off-by: Florian Westphal <fw@strlen.de>
> Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
> Signed-off-by: David S. Miller <davem@davemloft.net>
> Signed-off-by: Sasha Levin <sashal@kernel.org>

I have reported the following warnings and kernel crash on 5.10.26-rc2 [1]
The bisect reported that issue pointing out to this commit.

commit 460916534896e6d4f80a37152e0948db33376873
mptcp: put subflow sock on connect error

This problem is specific to 5.10.26-rc2.

Warning:
--------
[ 1040.114695] refcount_t: addition on 0; use-after-free.
[ 1040.119857] WARNING: CPU: 3 PID: 31925 at
/usr/src/kernel/lib/refcount.c:25 refcount_warn_saturate+0xd7/0x100
[ 1040.129769] Modules linked in: act_mirred cls_u32 sch_netem sch_etf
ip6table_nat xt_nat iptable_nat nf_nat ip6table_filter xt_conntrack
nf_conntrack nf_defrag_ipv4 libcrc32c ip6_tables nf_defrag_ipv6 sch_fq
iptable_filter xt_mark ip_tables cls_bpf sch_ingress algif_hash
x86_pkg_temp_thermal fuse [last unloaded: test_blackhole_dev]
[ 1040.159030] CPU: 3 PID: 31925 Comm: mptcp_connect Tainted: G
W K 5.10.26-rc2 #1
[ 1040.167459] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
2.2 05/23/2018
[ 1040.174851] RIP: 0010:refcount_warn_saturate+0xd7/0x100

And

Kernel Panic:
-------------
[ 1069.557485] BUG: kernel NULL pointer dereference, address: 0000000000000010
[ 1069.564446] #PF: supervisor read access in kernel mode
[ 1069.569583] #PF: error_code(0x0000) - not-present page
[ 1069.574714] PGD 0 P4D 0
[ 1069.577246] Oops: 0000 [#1] SMP PTI
[ 1069.580730] CPU: 1 PID: 17 Comm: ksoftirqd/1 Tainted: G W
K 5.10.26-rc2 #1
[ 1069.588719] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS
2.2 05/23/2018
[ 1069.596106] RIP: 0010:selinux_socket_sock_rcv_skb+0x3f/0x290
...
[ 1069.961697] Kernel panic - not syncing: Fatal exception in interrupt
[ 1069.968083] Kernel Offset: 0x18600000 from 0xffffffff81000000
(relocation range: 0xffffffff80000000-0xffffffffbfffffff)

steps to reproduce:
--------------------------
- cd /opt/kselftests/mainline/net/mptcp
- ./mptcp_join.sh || true

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>

crash test link:
https://lkft.validation.linaro.org/scheduler/job/2436164

Revert this commit and test job:
https://lkft.validation.linaro.org/scheduler/job/2437401#L1207

> ---
> net/mptcp/subflow.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
> index 16adba172fb9..591546d0953f 100644
> --- a/net/mptcp/subflow.c
> +++ b/net/mptcp/subflow.c
> @@ -1133,6 +1133,7 @@ int __mptcp_subflow_connect(struct sock *sk, const struct mptcp_addr_info *loc,
> spin_lock_bh(&msk->join_list_lock);
> list_add_tail(&subflow->node, &msk->join_list);
> spin_unlock_bh(&msk->join_list_lock);
> + sock_put(mptcp_subflow_tcp_sock(subflow));
>
> return err;
>

url:
[1] https://lore.kernel.org/stable/20210323182123.3ce89282@yaviniv.e18.physik.tu-muenchen.de/T/#m7994b86b52391a746e7d5be214885a5a1b2f9713

--
Linaro LKFT