In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: don't skip expired elements during walk
There is an asymmetry between commit/abort and preparation phase if the
following conditions are met:
- set is a verdict map ("1.2.3.4 : jump foo")
- timeouts are enabled
In this case, following sequence is problematic:
- element E in set S refers to chain C
- userspace requests removal of set S
- kernel does a set walk to decrement chain->use count for all elements
from preparation phase
- kernel does another set walk to remove elements from the commit phase
(or another walk to do a chain->use increment for all elements from
abort phase)
If E has already expired in 1), it will be ignored during list walk, so its use count
won't have been changed.
Then, when set is culled, ->destroy callback will zap the element via
nf_tables_set_elem_destroy(), but this function is only safe for
elements that have been deactivated earlier from the preparation phase:
lack of earlier deactivate removes the element but leaks the chain use
count, which results in a WARN splat when the chain gets removed later,
plus a leak of the nft_chain structure.
Update pipapo_get() not to skip expired elements, otherwise flush
command reports bogus ENOENT errors.
References
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: don't skip expired elements during walk
There is an asymmetry between commit/abort and preparation phase if the
following conditions are met:
In this case, following sequence is problematic:
from preparation phase
(or another walk to do a chain->use increment for all elements from
abort phase)
If E has already expired in 1), it will be ignored during list walk, so its use count
won't have been changed.
Then, when set is culled, ->destroy callback will zap the element via
nf_tables_set_elem_destroy(), but this function is only safe for
elements that have been deactivated earlier from the preparation phase:
lack of earlier deactivate removes the element but leaks the chain use
count, which results in a WARN splat when the chain gets removed later,
plus a leak of the nft_chain structure.
Update pipapo_get() not to skip expired elements, otherwise flush
command reports bogus ENOENT errors.
References