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

[Paolo Abeni <pabeni@redhat.com>]

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).

Paolo