netfilter: nft_payload: fix mask build for partial field offload

Overview

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

netfilter: nft_payload: fix mask build for partial field offload

nft_payload_offload_mask() builds the offload match mask for a payload expression that covers only part of a header field. For a partial IPv6 address match (field_len = 16, priv_len = 1) that shift is 1 << 120, which is undefined on the 32-bit int operand. It also trims only one word, so the remaining words stay 0xffffffff (and when priv_len is a multiple of 4 the trim is skipped entirely), leaving the mask covering more bytes than the rule matches.

UBSAN: shift-out-of-bounds in net/netfilter/nft_payload.c:278:20 shift exponent 120 is too large for 32-bit type 'int' ...

The match is byte-granular and struct nft_data is zero-initialised, so the correct mask is simply the first priv_len bytes set to 0xff. Set those bytes directly and drop the word/shift trimming; this removes the undefined shift and no longer over-masks the trailing bytes.

Affected

• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < 3ee7b3f813b11f28cd6efdf7f24d64b5a7fd4dc7
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < 8720df4504e0ed1781a702f65251bd47b3534d5e
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < 363c3a84a946d53e5e121c9f47c7c2b7d228c46b
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < b19b5d2e042c294e2cc1c908dc598f9d64015396
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < a375d8ace807767f29f276b681b6324c74929b1d
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < 16b553c46e347bc9de9946c4960654d5884a86de
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < 630295d5bba1d0e0f494cc459452eb0a0058c545
• Linux >= a5d45bc0dc50f9dd83703510e9804d813a9cac32 < 39e88f28fb32bf02bd4b525c24c842c9cff5663d
• Linux 5c2b4b4f9fa5b765b927e361e3d310bcb5773015
• Linux >= 5.9.14 < 5.10
• Linux 5.10

Remediation

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