Subject: Re: [Patch net-next] net_sched: fix a null pointer dereference in tcindex_set_parms()

From: John Fastabend <[email-masked]>
Date: Mon, 15 Sep 2014 17:15:28 -0700

On 09/15/2014 04:43 PM, Cong Wang wrote:
> This patch fixes the following crash:
>
> [   42.199159] BUG: unable to handle kernel NULL pointer dereference at 0000000000000018
> [   42.200027] IP: [<ffffffff817e3fc4>] tcindex_set_parms+0x45c/0x526
> [   42.200027] PGD d2319067 PUD d4ffe067 PMD 0
> [   42.200027] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
> [   42.200027] CPU: 0 PID: 541 Comm: tc Not tainted 3.17.0-rc4+ #603
> [   42.200027] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> [   42.200027] task: ffff8800d22d2670 ti: ffff8800ce790000 task.ti: ffff8800ce790000
> [   42.200027] RIP: 0010:[<ffffffff817e3fc4>]  [<ffffffff817e3fc4>] tcindex_set_parms+0x45c/0x526
> [   42.200027] RSP: 0018:ffff8800ce793898  EFLAGS: 00010202
> [   42.200027] RAX: 0000000000000001 RBX: ffff8800d1786498 RCX: 0000000000000000
> [   42.200027] RDX: ffffffff82114ec8 RSI: ffffffff82114ec8 RDI: ffffffff82114ec8
> [   42.200027] RBP: ffff8800ce793958 R08: 00000000000080d0 R09: 0000000000000001
> [   42.200027] R10: ffff8800ce7939a0 R11: 0000000000000246 R12: ffff8800d017d238
> [   42.200027] R13: 0000000000000018 R14: ffff8800d017c6a0 R15: ffff8800d1786620
> [   42.200027] FS:  00007f4e24539740(0000) GS:ffff88011a600000(0000) knlGS:0000000000000000
> [   42.200027] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   42.200027] CR2: 0000000000000018 CR3: 00000000cff38000 CR4: 00000000000006f0
> [   42.200027] Stack:
> [   42.200027]  ffff8800ce0949f0 0000000000000000 0000000200000003 ffff880000000000
> [   42.200027]  ffff8800ce7938b8 ffff8800ce7938b8 0000000600000007 0000000000000000
> [   42.200027]  ffff8800ce7938d8 ffff8800ce7938d8 0000000600000007 ffff8800ce0949f0
> [   42.200027] Call Trace:
> [   42.200027]  [<ffffffff817e4169>] tcindex_change+0xdb/0xee
> [   42.200027]  [<ffffffff817c16ca>] tc_ctl_tfilter+0x44d/0x63f
> [   42.200027]  [<ffffffff8179d161>] rtnetlink_rcv_msg+0x181/0x194
> [   42.200027]  [<ffffffff8179cf9d>] ? rtnl_lock+0x17/0x19
> [   42.200027]  [<ffffffff8179cfe0>] ? __rtnl_unlock+0x17/0x17
> [   42.200027]  [<ffffffff817ee296>] netlink_rcv_skb+0x49/0x8b
> [   43.462494]  [<ffffffff8179cfc2>] rtnetlink_rcv+0x23/0x2a
> [   43.462494]  [<ffffffff817ec8df>] netlink_unicast+0xc7/0x148
> [   43.462494]  [<ffffffff817ed413>] netlink_sendmsg+0x5cb/0x63d
> [   43.462494]  [<ffffffff810ad781>] ? mark_lock+0x2e/0x224
> [   43.462494]  [<ffffffff817757b8>] __sock_sendmsg_nosec+0x25/0x27
> [   43.462494]  [<ffffffff81778165>] sock_sendmsg+0x57/0x71
> [   43.462494]  [<ffffffff81152bbd>] ? might_fault+0x57/0xa4
> [   43.462494]  [<ffffffff81152c06>] ? might_fault+0xa0/0xa4
> [   43.462494]  [<ffffffff81152bbd>] ? might_fault+0x57/0xa4
> [   43.462494]  [<ffffffff817838fd>] ? verify_iovec+0x69/0xb7
> [   43.462494]  [<ffffffff817784f8>] ___sys_sendmsg+0x21d/0x2bb
> [   43.462494]  [<ffffffff81009db3>] ? native_sched_clock+0x35/0x37
> [   43.462494]  [<ffffffff8109ab53>] ? sched_clock_local+0x12/0x72
> [   43.462494]  [<ffffffff810ad781>] ? mark_lock+0x2e/0x224
> [   43.462494]  [<ffffffff8109ada4>] ? sched_clock_cpu+0xa0/0xb9
> [   43.462494]  [<ffffffff810aee37>] ? __lock_acquire+0x5fe/0xde4
> [   43.462494]  [<ffffffff8119f570>] ? rcu_read_lock_held+0x36/0x38
> [   43.462494]  [<ffffffff8119f75a>] ? __fcheck_files.isra.7+0x4b/0x57
> [   43.462494]  [<ffffffff8119fbf2>] ? __fget_light+0x30/0x54
> [   43.462494]  [<ffffffff81779012>] __sys_sendmsg+0x42/0x60
> [   43.462494]  [<ffffffff81779042>] SyS_sendmsg+0x12/0x1c
> [   43.462494]  [<ffffffff819d24d2>] system_call_fastpath+0x16/0x1b
>
> 'p->h' could be NULL while 'cp->h' is always update to date.
>
> Fixes: commit 331b72922c5f58d48fd ("net: sched: RCU cls_tcindex")
> Cc: John Fastabend <[email-masked]>
> Signed-off-by: Cong Wang <[email-masked]>
> ---
>   net/sched/cls_tcindex.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/sched/cls_tcindex.c b/net/sched/cls_tcindex.c
> index ee52542..5054fae 100644
> --- a/net/sched/cls_tcindex.c
> +++ b/net/sched/cls_tcindex.c
> @@ -381,7 +381,7 @@ tcindex_set_parms(struct net *net, struct tcf_proto *tp, unsigned long base,
>   		f->result = new_filter_result;
>   		f->next = NULL;
>
> -		fp = p->h + (handle % p->hash);
> +		fp = cp->h + (handle % cp->hash);
>   		for (nfp = rtnl_dereference(*fp);
>   		     nfp;
>   		     fp = &nfp->next, nfp = rtnl_dereference(*fp))
>

Thanks again.

Acked-By: John Fastabend <[email-masked]>

-- 
John Fastabend         Intel Corporation