netfilter: nf_tables: don't skip expired elements during walk

Overview

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:

1. set is a verdict map ("1.2.3.4 : jump foo")
2. timeouts are enabled

In this case, following sequence is problematic:

1. element E in set S refers to chain C
2. userspace requests removal of set S
3. kernel does a set walk to decrement chain->use count for all elements from preparation phase
4. 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.

Affected

• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < 94313a196b44184b5b52c1876da6a537701b425a
• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < 1da4874d05da1526b11b82fc7f3c7ac38749ddf8
• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < b15ea4017af82011dd55225ce77cce3d4dfc169c
• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < 7c7e658a36f8b1522bd3586d8137e5f93a25ddc5
• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < 59dab3bf0b8fc08eb802721c0532f13dd89209b8
• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < bd156ce9553dcaf2d6ee2c825d1a5a1718e86524
• Linux >= 9d0982927e79049675cb6c6c04a0ebb3dad5a434 < 24138933b97b055d486e8064b4a1721702442a9b
• Linux 4.1

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.