This is a note to let you know that I've just added the patch titled
netfilter: conntrack: fix rmmod double-free race
to the 6.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
netfilter-conntrack-fix-rmmod-double-free-race.patch
and it can be found in the queue-6.2 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit d5757439015324c677b9f554dfdad7d70f69b049
Author: Florian Westphal <fw@xxxxxxxxx>
Date: Tue Feb 14 17:23:59 2023 +0100
netfilter: conntrack: fix rmmod double-free race
[ Upstream commit e6d57e9ff0aec323717ee36fc9ea34ad89217151 ]
nf_conntrack_hash_check_insert() callers free the ct entry directly, via
nf_conntrack_free.
This isn't safe anymore because
nf_conntrack_hash_check_insert() might place the entry into the conntrack
table and then delteted the entry again because it found that a conntrack
extension has been removed at the same time.
In this case, the just-added entry is removed again and an error is
returned to the caller.
Problem is that another cpu might have picked up this entry and
incremented its reference count.
This results in a use-after-free/double-free, once by the other cpu and
once by the caller of nf_conntrack_hash_check_insert().
Fix this by making nf_conntrack_hash_check_insert() not fail anymore
after the insertion, just like before the 'Fixes' commit.
This is safe because a racing nf_ct_iterate() has to wait for us
to release the conntrack hash spinlocks.
While at it, make the function return -EAGAIN in the rmmod (genid
changed) case, this makes nfnetlink replay the command (suggested
by Pablo Neira).
Fixes: c56716c69ce1 ("netfilter: extensions: introduce extension genid count")
Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/net/netfilter/nf_conntrack_bpf.c b/net/netfilter/nf_conntrack_bpf.c
index 24002bc61e07e..e1af14e3b63c5 100644
--- a/net/netfilter/nf_conntrack_bpf.c
+++ b/net/netfilter/nf_conntrack_bpf.c
@@ -381,7 +381,6 @@ struct nf_conn *bpf_ct_insert_entry(struct nf_conn___init *nfct_i)
struct nf_conn *nfct = (struct nf_conn *)nfct_i;
int err;
- nfct->status |= IPS_CONFIRMED;
err = nf_conntrack_hash_check_insert(nfct);
if (err < 0) {
nf_conntrack_free(nfct);
diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 496c4920505b3..ead11a9c261f3 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -886,10 +886,8 @@ nf_conntrack_hash_check_insert(struct nf_conn *ct)
zone = nf_ct_zone(ct);
- if (!nf_ct_ext_valid_pre(ct->ext)) {
- NF_CT_STAT_INC_ATOMIC(net, insert_failed);
- return -ETIMEDOUT;
- }
+ if (!nf_ct_ext_valid_pre(ct->ext))
+ return -EAGAIN;
local_bh_disable();
do {
@@ -924,6 +922,19 @@ nf_conntrack_hash_check_insert(struct nf_conn *ct)
goto chaintoolong;
}
+ /* If genid has changed, we can't insert anymore because ct
+ * extensions could have stale pointers and nf_ct_iterate_destroy
+ * might have completed its table scan already.
+ *
+ * Increment of the ext genid right after this check is fine:
+ * nf_ct_iterate_destroy blocks until locks are released.
+ */
+ if (!nf_ct_ext_valid_post(ct->ext)) {
+ err = -EAGAIN;
+ goto out;
+ }
+
+ ct->status |= IPS_CONFIRMED;
smp_wmb();
/* The caller holds a reference to this object */
refcount_set(&ct->ct_general.use, 2);
@@ -932,12 +943,6 @@ nf_conntrack_hash_check_insert(struct nf_conn *ct)
NF_CT_STAT_INC(net, insert);
local_bh_enable();
- if (!nf_ct_ext_valid_post(ct->ext)) {
- nf_ct_kill(ct);
- NF_CT_STAT_INC_ATOMIC(net, drop);
- return -ETIMEDOUT;
- }
-
return 0;
chaintoolong:
NF_CT_STAT_INC(net, chaintoolong);
diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index ca4d5bb1ea524..733bb56950c14 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -2316,9 +2316,6 @@ ctnetlink_create_conntrack(struct net *net,
nfct_seqadj_ext_add(ct);
nfct_synproxy_ext_add(ct);
- /* we must add conntrack extensions before confirmation. */
- ct->status |= IPS_CONFIRMED;
-
if (cda[CTA_STATUS]) {
err = ctnetlink_change_status(ct, cda);
if (err < 0)
