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From: Florian Westphal <fw@strlen.de>
To: <netfilter-devel@vger.kernel.org>
Cc: Florian Westphal <fw@strlen.de>
Subject: [PATCH nf-next 3/4] netfilter: nf_queue: do not release refcouts until nf_reinject is done
Date: Fri, 27 Mar 2020 03:24:48 +0100
Message-ID: <20200327022449.7411-4-fw@strlen.de> (raw)
In-Reply-To: <20200327022449.7411-1-fw@strlen.de>

nf_queue is problematic when another NF_QUEUE invocation happens
from nf_reinject().

1. nf_queue is invoked, increments state->sk refcount.
2. skb is queued, waiting for verdict.
3. sk is closed/released.
3. verdict comes back, nf_reinject is called.
4. nf_reinject drops the reference -- refcount can now drop to 0

Instead of get_ref/release_ref pattern, we need to nest the get_ref calls:
    get_ref
       get_ref
       release_ref
     release_ref

So that when we invoke the next processing stage (another netfilter
or the okfn()), we hold at least one reference count on the
devices/socket.

After previous patch, it is now safe to put the entry even after okfn()
has potentially free'd the skb.

Signed-off-by: Florian Westphal <fw@strlen.de>
---
 net/netfilter/nf_queue.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_queue.c b/net/netfilter/nf_queue.c
index 96eb72908467..aadccdd117f0 100644
--- a/net/netfilter/nf_queue.c
+++ b/net/netfilter/nf_queue.c
@@ -303,12 +303,10 @@ void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict)
 
 	hooks = nf_hook_entries_head(net, pf, entry->state.hook);
 
-	nf_queue_entry_release_refs(entry);
-
 	i = entry->hook_index;
 	if (WARN_ON_ONCE(!hooks || i >= hooks->num_hook_entries)) {
 		kfree_skb(skb);
-		kfree(entry);
+		nf_queue_entry_free(entry);
 		return;
 	}
 
@@ -347,6 +345,6 @@ void nf_reinject(struct nf_queue_entry *entry, unsigned int verdict)
 		kfree_skb(skb);
 	}
 
-	kfree(entry);
+	nf_queue_entry_free(entry);
 }
 EXPORT_SYMBOL(nf_reinject);
-- 
2.24.1


  parent reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-27  2:24 [PATCH nf-next 0/4] netfilter: nf_queue: rework refcount handling Florian Westphal
2020-03-27  2:24 ` [PATCH nf-next 1/4] netfilter: nf_queue: make nf_queue_entry_release_refs static Florian Westphal
2020-03-27  2:24 ` [PATCH nf-next 2/4] netfilter: nf_queue: place bridge physports into queue_entry struct Florian Westphal
2020-03-27  2:24 ` Florian Westphal [this message]
2020-03-27  2:24 ` [PATCH nf-next 4/4] netfilter: nf_queue: prefer nf_queue_entry_free Florian Westphal
2020-03-29 15:07 ` [PATCH nf-next 0/4] netfilter: nf_queue: rework refcount handling Pablo Neira Ayuso

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