Re: netfilter: nf_conntrack: there maybe a bug in __nf_conntrack_confirm, when it race against get_next_corpse

On Tue, 4 Nov 2014 09:48:32 +0800
"billbonaparte" [off-list ref] wrote:

(sorry to send this e-mail again, last mail is rejected by server due to
non-acceptable content)

There is several issues with your submission.  I'll take care of
resubmitting a patch in your name (so you will get credit in the git
log).

If you care to know, issues are:
 1. you are not sending to the appropriate mailing lists,
 2. patch is as an attachment (should be inlined),
 3. the patch have style and white-space issues.

Florian Westphal [mailto:fw@strlen.de] wrote:

quoted

Correct.  This is broken since the central spin lock removal, since 
nf_conntrack_lock no longer protects both get_next_corpse and 
conntrack_confirm.

Please send a patch, moving dying check after removal of conntrack from 
the percpu list,

Since unconfirmed conntrack is stored in unconfirmed-list which is per-cpu
list and protected by per-cpu spin-lock, we can remove it from
uncomfirmed-list and insert it into ct-hash-table separately. that is to
say, we can remove it from uncomfirmed-list without holding corresponding
hash-lock, then check if it is dying.
if it is dying, we add it to the dying-list, then quit
__nf_conntrack_confirm. we do this to follow the rules that the conntrack
must alternatively at unconfirmed-list or dying-list when it is abort to be
destroyed.

In the resubmit. I'll take a slightly more conservative approach, by
keeping the DYING check under the hash-lock, as it is currently.  I
guess we could do it without holding the hash-lock, but I want to keep
the fix as simple as possible.

quoted

quoted

	2. operation on ct->status should be atomic, because it race aginst 
get_next_corpse.

[...]

if there is a race at operating ct->status, there will be in alternative
case:
1) IPS_DYING bit which set in get_next_corpse override other bits (e.g.
IPS_SRC_NAT_DONE_BIT), or
2) other bits (e.g. IPS_SRC_NAT_DONE_BIT) which set in nf_nat_setup_info
override IPS_DYING bit.

Notice the set_bit() is atomic, so we don't have these issues (of bits
getting overridden).

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Sr. Network Kernel Developer at Red Hat
  Author of http://www.iptv-analyzer.org
  LinkedIn: http://www.linkedin.com/in/brouer