netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent

Overview

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

netfilter: ctnetlink: zero expect NAT fields when CTA_EXPECT_NAT absent

ctnetlink_alloc_expect() allocates expectations from a non-zeroing slab cache via nf_ct_expect_alloc(). When CTA_EXPECT_NAT is not present in the netlink message, saved_addr and saved_proto are never initialized. Stale data from a previous slab occupant can then be dumped to userspace by ctnetlink_exp_dump_expect(), which checks these fields to decide whether to emit CTA_EXPECT_NAT.

The safe sibling nf_ct_expect_init(), used by the packet path, explicitly zeroes these fields.

Zero saved_addr, saved_proto and dir in the else branch, guarded by IS_ENABLED(CONFIG_NF_NAT) since these fields only exist when NAT is enabled.

Confirmed by priming the expect slab with NAT-bearing expectations, freeing them, creating a new expectation without CTA_EXPECT_NAT, and observing that the ctnetlink dump emits a spurious CTA_EXPECT_NAT containing stale data from the prior allocation.

Affected

• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < a5a89db6981a1ddf2314bf50cb49db5a3146185f
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < 1c2ebdeff8d088a2e47ae25d7b38447249adace2
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < a64b7bf84b4d5ea54218c5d374ec87fff9000f43
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < 2898080c054ea4d6ddfaaf21bbedbc229a9a8376
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < fd002ff2ea030cbfb0188a11b3c60ce7f84485f4
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < 929f7a9a7aad9404a5867216c3f8738232355b38
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < bff0f4f06f12d6d9bc565a3e1378abd4f6f5ce36
• Linux >= 076a0ca02644657b13e4af363f487ced2942e9cb < 35177c6877134a21315f37d57a5577846225623e
• Linux 3.4

Remediation

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