Patch "netfilter: nfnetlink_cthelper: hit EBUSY on updates if size mismatches" has been added to the 4.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    netfilter: nfnetlink_cthelper: hit EBUSY on updates if size mismatches

to the 4.4-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-nfnetlink_cthelper-hit-ebusy-on-updates-if.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 15fdf8b4c289e0a6f7b7e53a2f5476ad3d83b3d2
Author: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Date:   Fri May 28 13:45:16 2021 +0200

    netfilter: nfnetlink_cthelper: hit EBUSY on updates if size mismatches
    
    [ Upstream commit 8971ee8b087750a23f3cd4dc55bff2d0303fd267 ]
    
    The private helper data size cannot be updated. However, updates that
    contain NFCTH_PRIV_DATA_LEN might bogusly hit EBUSY even if the size is
    the same.
    
    Fixes: 12f7a505331e ("netfilter: add user-space connection tracking helper infrastructure")
    Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netfilter/nfnetlink_cthelper.c b/net/netfilter/nfnetlink_cthelper.c
index 8c1733869343..63a9d5fd00c0 100644
--- a/net/netfilter/nfnetlink_cthelper.c
+++ b/net/netfilter/nfnetlink_cthelper.c
@@ -355,10 +355,14 @@ static int
 nfnl_cthelper_update(const struct nlattr * const tb[],
 		     struct nf_conntrack_helper *helper)
 {
+	u32 size;
 	int ret;
 
-	if (tb[NFCTH_PRIV_DATA_LEN])
-		return -EBUSY;
+	if (tb[NFCTH_PRIV_DATA_LEN]) {
+		size = ntohl(nla_get_be32(tb[NFCTH_PRIV_DATA_LEN]));
+		if (size != helper->data_len)
+			return -EBUSY;
+	}
 
 	if (tb[NFCTH_POLICY]) {
 		ret = nfnl_cthelper_update_policy(helper, tb[NFCTH_POLICY]);