[PATCH nf] netfilter: nf_tables: fix device name and prefix match in hook lookup

[Fernando Fernandez Mancera <fmancera@suse.de>]

Currently, a netdev chain or flowtable hooked to a device prefix can be
unintentionally deleted or updated by a control-plane request targeting
an exact device name or even a shorter one due to the usage of min() to
calculate the length to match.

Fix this by making sure an exact device match never matches a prefix and
that both the target and the candidate have the same length.

Reported-by: Wei Fang <void0red@gmail.com>
Closes: https://lore.kernel.org/netfilter-devel/CANE+tVrDeNCHQVmsqkV2ozeBqyE3GtRDMhZgsg1bhw10yGNTRQ@mail.gmail.com/
Fixes: 6d07a289504a ("netfilter: nf_tables: Support wildcard netdev hook specs")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
---
 net/netfilter/nf_tables_api.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index af357f6c5070..e2b18c4722fc 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -1973,7 +1973,7 @@ static int nft_dump_stats(struct sk_buff *skb, struct nft_stats __percpu *stats)
 	return -ENOSPC;
 }
 
-static bool hook_is_prefix(struct nft_hook *hook)
+static bool hook_is_prefix(const struct nft_hook *hook)
 {
 	return strlen(hook->ifname) >= hook->ifnamelen;
 }
@@ -2440,8 +2440,11 @@ static struct nft_hook *nft_hook_list_find(struct list_head *hook_list,
 	struct nft_hook *hook;
 
 	list_for_each_entry(hook, hook_list, list) {
-		if (!strncmp(hook->ifname, this->ifname,
-			     min(hook->ifnamelen, this->ifnamelen))) {
+		if (hook_is_prefix(hook) != hook_is_prefix(this))
+			continue;
+		if (hook->ifnamelen != this->ifnamelen)
+			continue;
+		if (!strncmp(hook->ifname, this->ifname, hook->ifnamelen)) {
 			if (hook->flags & NFT_HOOK_REMOVE)
 				continue;
 
-- 
2.55.0