CVE-2021-3600: Divide by Zero

It was discovered that eBPF 32-bit div/mod source register truncation could lead to out-of-bounds reads and writes in the kernel. It was introduced by commit 68fda450a7df ("bpf: fix 32-bit divide by zero"). It was first introduced in 4.15-rc9, but backported and applied to v4.14.y, v4.9.y and v4.4.y. However, this specific attack will not work on v4.4.y and v4.9.y kernels as pointer arithmetic is prohibited on those kernels. This was introduced by commit f1174f77b50c ("bpf/verifier: rework value tracking"), in v4.14-rc1. The fix is commit e88b2c6e5a4d ("bpf: Fix 32 bit src register truncation on div/mod"), introduced in v5.11. It was backported and applied on v5.10.y and v5.4.y, but not v4.19.y and v4.14.y.

Reference: https://www.openwall.com/lists/oss-security/2021/06/23/1

— Red Hat

It was discovered that the eBPF implementation in the Linux kernel did not properly track bounds information for 32 bit registers when performing div and mod operations. A local attacker could use this to possibly execute arbitrary code.

— Launchpad