CVE-2021-3490 - Linux kernel eBPF bitwise ops ALU32 bounds tracking

[Thadeu Lima de Souza Cascardo <cascardo () canonical com>]

It was discovered that eBPF ALU32 bounds tracking for bitwise ops (AND, OR and
XOR) did not update the 32-bit bounds.

Manfred Paul (@_manfp) of the RedRocket CTF team (@redrocket_ctf) working with
Trend Micro's Zero Day Initiative discovered that this vulnerability could be
turned into out-of-bounds reads and writes in the kernel. This has been
reported as ZDI-CAN-13590, and assigned CVE-2021-3490.

It was introduced by commit 3f50f132d840 ("bpf: Verifier, do explicit ALU32
bounds tracking"). The XOR version was introduced by commit 2921c90d4718 ("bpf:
Fix a verifier failure with xor"). The first one was introduced in 5.7-rc1,
while the latter was introduced in 5.10-rc1. There has been no backport to any
upstream LTS kernel.

This was fixed by commit:
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/commit/?id=049c4e13714ecbca567b4d5f6d563f05d431c80e

Cascardo.