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[188.141.5.72]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-490428f6786sm48617045e9.25.2026.05.23.08.26.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 23 May 2026 08:26:24 -0700 (PDT) From: David Carlier To: pablo@netfilter.org, fw@strlen.de, kadlec@netfilter.org Cc: phil@nwl.cc, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, David Carlier Subject: [PATCH nf] netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag Date: Sat, 23 May 2026 16:26:21 +0100 Message-ID: <20260523152621.58576-1-devnexen@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The DEV_PATH_BR_VLAN_UNTAG case post-decrements info->num_encaps inside WARN_ON_ONCE(). num_encaps is u8, so if it's already 0 the decrement still happens and wraps it to 255. The break only leaves the inner switch -- a later path entry can set info->indev back to a real device, and we end up returning with num_encaps == 255. nft_dev_forward_path() then walks info.encap[] (size 2) up to num_encaps, which means an OOB stack read and a bogus count copied into the route descriptor. Should only happen on a malformed bridge path stack, hence the WARN, but worth handling sanely. Move the decrement out of the WARN. Fixes: e990cef6516d ("netfilter: flowtable: add bridge vlan filtering support") Signed-off-by: David Carlier --- net/netfilter/nf_flow_table_path.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nf_flow_table_path.c b/net/netfilter/nf_flow_table_path.c index 9e88ea6a2eef..6263e07a1276 100644 --- a/net/netfilter/nf_flow_table_path.c +++ b/net/netfilter/nf_flow_table_path.c @@ -163,10 +163,11 @@ static void nft_dev_path_info(const struct net_device_path_stack *stack, info->num_encaps++; break; case DEV_PATH_BR_VLAN_UNTAG: - if (WARN_ON_ONCE(info->num_encaps-- == 0)) { + if (WARN_ON_ONCE(info->num_encaps == 0)) { info->indev = NULL; break; } + info->num_encaps--; break; case DEV_PATH_BR_VLAN_KEEP: break; -- 2.53.0