diff options
| author | Kamil Sawicki <user148783812897@gmail.com> | 2026-10-23 20:48:35 -0400 |
|---|---|---|
| committer | Jakub Kicinski <kuba@kernel.org> | 2026-10-27 15:24:49 -0700 |
| commit | d3ff07f5acc573e5f72bf1c581bae5d05191ba61 (patch) | |
| tree | 6ccd60f7a96a813a33f40046fd98bfc78a49c0ef /net | |
| parent | 573a6d4c7a21e34d7a2174b8d3c7ca67a5e850b6 (diff) | |
net: limit priority VLAN untag depth
The priority VLAN receive path can repeatedly remove VID 0 tags and retry
packet processing. Unlike the read-only VLAN protocol parser, this path has
no limit on the number of nested tags it consumes.
Each skb_vlan_untag() advances skb->data and resets header offsets. The
offsets are stored in 16-bit fields. With enough nested tags, the network
or transport offset can wrap. A later protocol handler can then derive a
large pull length from the wrapped offsets and access memory outside the
skb allocation.
Apply the existing VLAN_MAX_DEPTH limit to the exceptional VID 0 retry.
Count the tag already stored in skb VLAN metadata as the first level, then
stop before untagging a ninth level. Keep the accounting inside this
uncommon branch so the regular VLAN receive path is unaffected.
A single VID 0 priority tag before a real VLAN tag is valid. No normal
deployment was found that intentionally emits multiple consecutive VID 0
tags; permitting eight levels is therefore conservative.
The issue was found while researching the Linux network receive path for
Google kvmCTF, with OpenAI Codex (gpt-5.6-sol) assisting the analysis. The
affected path, reproducer and fix were manually reviewed and tested.
Fixes: 36b2f61a42c2 ("net: handle 802.1P vlan 0 packets properly")
Cc: stable@vger.kernel.org
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Kamil Sawicki <user148783812897@gmail.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: Eric Dumazet <edumazet@kernel.org>
Link: https://patch.msgid.link/20261024004835.17862-1-user148783812897@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net')
| -rw-r--r-- | net/core/dev.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/net/core/dev.c b/net/core/dev.c index 9021e6d36ab2..b3622e532f26 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6315,6 +6315,8 @@ skip_classify: } if (unlikely(skb_vlan_tag_present(skb)) && !netdev_uses_dsa(skb->dev)) { + unsigned int priority_tag_depth = 1; + check_vlan_id: if (skb_vlan_tag_get_id(skb)) { /* Vlan id is non 0 and vlan_do_receive() above couldn't @@ -6326,6 +6328,12 @@ check_vlan_id: * 802.1Q or 802.1AD and vlan_do_receive() above could * not find vlan dev for vlan id 0. */ + if (unlikely(priority_tag_depth >= VLAN_MAX_DEPTH)) { + drop_reason = SKB_DROP_REASON_RECURSION_LIMIT; + goto drop; + } + + priority_tag_depth++; __vlan_hwaccel_clear_tag(skb); skb = skb_vlan_untag(skb); if (unlikely(!skb)) |