netfilter: nft_set_pipapo: fix stack out-of-bounds read in pipapo_drop()

Overview

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

netfilter: nft_set_pipapo: fix stack out-of-bounds read in pipapo_drop()

pipapo_drop() passes rulemap[i + 1].n to pipapo_unmap() as the to_offset argument on every iteration, including the last one where i == m->field_count - 1. This reads one element past the end of the stack-allocated rulemap array (declared as rulemap[NFT_PIPAPO_MAX_FIELDS] with NFT_PIPAPO_MAX_FIELDS == 16).

Although pipapo_unmap() returns early when is_last is true without using the to_offset value, the argument is evaluated at the call site before the function body executes, making this a genuine out-of-bounds stack read confirmed by KASAN:

BUG: KASAN: stack-out-of-bounds in pipapo_drop+0x50c/0x57c [nf_tables] Read of size 4 at addr ffff8000810e71a4

This frame has 1 object: [32, 160) 'rulemap'

The buggy address is at offset 164 -- exactly 4 bytes past the end of the rulemap array.

Pass 0 instead of rulemap[i + 1].n on the last iteration to avoid the out-of-bounds read.

Affected

• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 1957e793196e7f8557374fd4eda53abcbb42e1c0
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 57fb87ca095d5127cd7a27583b8ec43dcf7c9e9e
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 60c1d18781e37bfb96290b86510eb01c5fa24d75
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 0a55d62cdb628923d8a21724374a70c76ac7d19d
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < dfbdac719198778b581bc0dd055df2542edb8c62
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < e047f6fbb975f685d6c9fcef95b3b7787a79b46d
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 324b749aa5b2d516ccfab933df9d3f56e7807f5f
• Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < d6d8cd2db236a9dd13dbc2d05843b3445cc964b5
• Linux 5.6

Remediation

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