Re: [PATCH v3] net: sched: fix memory leak in tcindex_set_parms

[Hawkins Jiawei <yin31149@gmail.com>]

On Thu, 1 Dec 2022 at 18:24, Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Tue, 2022-11-29 at 10:52 +0800, Hawkins Jiawei wrote:
> > Syzkaller reports a memory leak as follows:
> > ====================================
> > BUG: memory leak
> > unreferenced object 0xffff88810c287f00 (size 256):
> >   comm "syz-executor105", pid 3600, jiffies 4294943292 (age 12.990s)
> >   hex dump (first 32 bytes):
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
> >   backtrace:
> >     [<ffffffff814cf9f0>] kmalloc_trace+0x20/0x90 mm/slab_common.c:1046
> >     [<ffffffff839c9e07>] kmalloc include/linux/slab.h:576 [inline]
> >     [<ffffffff839c9e07>] kmalloc_array include/linux/slab.h:627 [inline]
> >     [<ffffffff839c9e07>] kcalloc include/linux/slab.h:659 [inline]
> >     [<ffffffff839c9e07>] tcf_exts_init include/net/pkt_cls.h:250 [inline]
> >     [<ffffffff839c9e07>] tcindex_set_parms+0xa7/0xbe0 net/sched/cls_tcindex.c:342
> >     [<ffffffff839caa1f>] tcindex_change+0xdf/0x120 net/sched/cls_tcindex.c:553
> >     [<ffffffff8394db62>] tc_new_tfilter+0x4f2/0x1100 net/sched/cls_api.c:2147
> >     [<ffffffff8389e91c>] rtnetlink_rcv_msg+0x4dc/0x5d0 net/core/rtnetlink.c:6082
> >     [<ffffffff839eba67>] netlink_rcv_skb+0x87/0x1d0 net/netlink/af_netlink.c:2540
> >     [<ffffffff839eab87>] netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
> >     [<ffffffff839eab87>] netlink_unicast+0x397/0x4c0 net/netlink/af_netlink.c:1345
> >     [<ffffffff839eb046>] netlink_sendmsg+0x396/0x710 net/netlink/af_netlink.c:1921
> >     [<ffffffff8383e796>] sock_sendmsg_nosec net/socket.c:714 [inline]
> >     [<ffffffff8383e796>] sock_sendmsg+0x56/0x80 net/socket.c:734
> >     [<ffffffff8383eb08>] ____sys_sendmsg+0x178/0x410 net/socket.c:2482
> >     [<ffffffff83843678>] ___sys_sendmsg+0xa8/0x110 net/socket.c:2536
> >     [<ffffffff838439c5>] __sys_sendmmsg+0x105/0x330 net/socket.c:2622
> >     [<ffffffff83843c14>] __do_sys_sendmmsg net/socket.c:2651 [inline]
> >     [<ffffffff83843c14>] __se_sys_sendmmsg net/socket.c:2648 [inline]
> >     [<ffffffff83843c14>] __x64_sys_sendmmsg+0x24/0x30 net/socket.c:2648
> >     [<ffffffff84605fd5>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >     [<ffffffff84605fd5>] do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
> >     [<ffffffff84800087>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > ====================================
> >
> > Kernel uses tcindex_change() to change an existing
> > filter properties. During the process of changing,
> > kernel uses tcindex_alloc_perfect_hash() to newly
> > allocate filter results, uses tcindex_filter_result_init()
> > to clear the old filter result.
> >
> > Yet the problem is that, kernel clears the old
> > filter result, without destroying its tcf_exts structure,
> > which triggers the above memory leak.
> >
> > Considering that there already extis a tc_filter_wq workqueue
> > to destroy the old tcindex_data by tcindex_partial_destroy_work()
> > at the end of tcindex_set_parms(), this patch solves this memory
> > leak bug by removing this old filter result clearing part,
> > and delegating it to the tc_filter_wq workqueue.
> >
> > [Thanks to the suggestion from Jakub Kicinski, Cong Wang, Paolo Abeni
> > and Dmitry Vyukov]
> >
> > Fixes: b9a24bb76bf6 ("net_sched: properly handle failure case of tcf_exts_init()")
> > Link: https://lore.kernel.org/all/0000000000001de5c505ebc9ec59@google.com/
> > Reported-by: syzbot+232ebdbd36706c965ebf@syzkaller.appspotmail.com
> > Tested-by: syzbot+232ebdbd36706c965ebf@syzkaller.appspotmail.com
> > Cc: Cong Wang <cong.wang@bytedance.com>
> > Cc: Jakub Kicinski <kuba@kernel.org>
> > Cc: Paolo Abeni <pabeni@redhat.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
>
> The patch looks correct to me, but we are very late in this release
> cycle, and I fear there is a chance of introducing some regression. The
> issue addressed here is present since quite some time, I suggest to
> postpone this fix to the beginning of the next release cycle.
>
> Please, repost this patch after that 6.1 is released, thanks! (And feel
> free to add my Acked-by).

Thanks for your review.

I will retest this patch after 6.1, and repost this patch
if the patch works fine.

>
> Paolo
>