On Wed, Jul 12, 2017 at 3:30 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote: > On Sun, Jul 9, 2017 at 4:57 PM, Dave Jones <da...@codemonkey.org.uk> wrote: >> The new refcount debugging code spews this twice during boot on my router.. >> >> >> refcount_t: increment on 0; use-after-free. >> ------------[ cut here ]------------ >> WARNING: CPU: 1 PID: 17 at lib/refcount.c:152 refcount_inc+0x2b/0x30 >> CPU: 1 PID: 17 Comm: ksoftirqd/1 Not tainted 4.12.0-firewall+ #8 >> task: ffff8801d4441ac0 task.stack: ffff8801d4450000 >> RIP: 0010:refcount_inc+0x2b/0x30 >> RSP: 0018:ffff8801d4456da8 EFLAGS: 00010046 >> RAX: 000000000000002c RBX: ffff8801d4c3cf40 RCX: 0000000000000000 >> RDX: 000000000000002c RSI: 0000000000000003 RDI: ffffed003a88adab >> RBP: ffff8801d4456da8 R08: 0000000000000003 R09: fffffbfff4afcb57 >> R10: 0000000000000000 R11: fffffbfff4afcb58 R12: ffff8801d4c3c540 >> R13: 0000000000000082 R14: ffff8801ce9c7ff8 R15: ffff8801ce9c8aa0 >> FS: 0000000000000000(0000) GS:ffff8801d6a00000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> CR2: 00007fa2b803156e CR3: 00000001c405d000 CR4: 00000000000406e0 >> Call Trace: >> zap_completion_queue+0xad/0x1a0 > > > Sigh... it is on purpose: > > commit 8a455b087c9629b3ae3b521b4f1ed16672f978cc > Author: Jarek Poplawski <jark...@gmail.com> > Date: Thu Mar 20 16:07:27 2008 -0700 > > netpoll: zap_completion_queue: adjust skb->users counter > > zap_completion_queue() retrieves skbs from completion_queue where they > have > zero skb->users counter. Before dev_kfree_skb_any() it should be non-zero > yet, so it's increased now. > > Reported-and-tested-by: Andrew Morton <a...@linux-foundation.org> > Signed-off-by: Jarek Poplawski <jark...@gmail.com> > Signed-off-by: Andrew Morton <a...@linux-foundation.org> > Signed-off-by: David S. Miller <da...@davemloft.net> > > We need to review it now. :-/
I think we should explicitly set it to 1 with refcount_set() since we know it was 0 for sure. diff --git a/net/core/netpoll.c b/net/core/netpoll.c index d3408a6..8357f16 100644 --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -277,7 +277,7 @@ static void zap_completion_queue(void) struct sk_buff *skb = clist; clist = clist->next; if (!skb_irq_freeable(skb)) { - refcount_inc(&skb->users); + refcount_set(&skb->users, 1); dev_kfree_skb_any(skb); /* put this one back */ } else { __kfree_skb(skb);