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Date: Sun, 6 Nov 2022 22:55:31 +0800 From: Hawkins Jiawei <yin31149@...il.com> To: xiyou.wangcong@...il.com Cc: 18801353760@....com, davem@...emloft.net, edumazet@...gle.com, jhs@...atatu.com, jiri@...nulli.us, kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, pabeni@...hat.com, syzbot+232ebdbd36706c965ebf@...kaller.appspotmail.com, syzkaller-bugs@...glegroups.com, yin31149@...il.com Subject: Re: [PATCH] net: sched: fix memory leak in tcindex_set_parms Hi Cong, On Sun, 6 Nov 2022 at 03:50, Cong Wang <xiyou.wangcong@...il.com> wrote: > > On Mon, Oct 31, 2022 at 02:08:35PM +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 will uses tcindex_change() to change an existing > > traffic-control-indices filter properties. During the > > process of changing, kernel will clears the old > > traffic-control-indices filter result, and updates it > > by RCU assigning new traffic-control-indices data. > > > > Yet the problem is that, kernel will clears the old > > traffic-control-indices filter result, without destroying > > its tcf_exts structure, which triggers the above > > memory leak. > > > > This patch solves it by using tcf_exts_destroy() to > > destroy the tcf_exts structure in old > > traffic-control-indices filter result. > > So... your patch can be just the following one-liner, right? Yes, as you and Jakub points out, all ifdefs can be removed, and I will refactor those in v2 patch. > > > diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c > index 1c9eeb98d826..00a6c04a4b42 100644 > --- a/net/sched/cls_tcindex.c > +++ b/net/sched/cls_tcindex.c > @@ -479,6 +479,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base, > } > > if (old_r && old_r != r) { > + tcf_exts_destroy(&old_r->exts); > err = tcindex_filter_result_init(old_r, cp, net); > if (err < 0) { > kfree(f); As for the position of the tcf_exts_destroy(), should we call it after the RCU updating, after `rcu_assign_pointer(tp->root, cp)` ? Or the concurrent RCU readers may derefer this freed memory (Please correct me If I am wrong).
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