CVE-2026-80634

In the Linux kernel, the following vulnerability has been resolved:

netfilter: flowtable: avoid num_encaps underflow on bridge VLAN untag

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.

[ While at this, remove the WARN_ON_ONCE since this can only happen

with a buggy bridge path stack --pablo ].