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SubjectRe: [PATCH] ipv4: fix a RCU-list bug in inet_dump_fib()
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On 3/19/20 4:11 PM, Qian Cai wrote:
> There is a place,
>
> inet_dump_fib()
> fib_table_dump
> fn_trie_dump_leaf()
> hlist_for_each_entry_rcu()
>
> without rcu_read_lock() triggers a warning,
>
> WARNING: suspicious RCU usage
> -----------------------------
> net/ipv4/fib_trie.c:2216 RCU-list traversed in non-reader section!!
>
> other info that might help us debug this:
>
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by ip/1923:
> #0: ffffffff8ce76e40 (rtnl_mutex){+.+.}, at: netlink_dump+0xd6/0x840
>
> Call Trace:
> dump_stack+0xa1/0xea
> lockdep_rcu_suspicious+0x103/0x10d
> fn_trie_dump_leaf+0x581/0x590
> fib_table_dump+0x15f/0x220
> inet_dump_fib+0x4ad/0x5d0
> netlink_dump+0x350/0x840
> __netlink_dump_start+0x315/0x3e0
> rtnetlink_rcv_msg+0x4d1/0x720
> netlink_rcv_skb+0xf0/0x220
> rtnetlink_rcv+0x15/0x20
> netlink_unicast+0x306/0x460
> netlink_sendmsg+0x44b/0x770
> __sys_sendto+0x259/0x270
> __x64_sys_sendto+0x80/0xa0
> do_syscall_64+0x69/0xf4
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>

Fixes: 18a8021a7be3 ("net/ipv4: Plumb support for filtering route dumps")

but you have a problem below ...

> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> net/ipv4/fib_frontend.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
> index 577db1d50a24..5e441282d647 100644
> --- a/net/ipv4/fib_frontend.c
> +++ b/net/ipv4/fib_frontend.c
> @@ -987,6 +987,8 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
> if (filter.flags & RTM_F_PREFIX)
> return skb->len;
>
> + rcu_read_lock();
> +
> if (filter.table_id) {
> tb = fib_get_table(net, filter.table_id);
> if (!tb) {

this branch has 2 return points which now have rcu_read_lock; you should
have seen this when you tested the change..


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