Seen it. Not surprising at all, but hopefully useful as a learning experience.
On 10 Apr 2021, at 10:24, Peter Müller peter.mueller@ipfire.org wrote:
And *BOOM* goes the dynamite... m(
An issue has been discovered in the Linux kernel that can be abused by unprivileged local users to escalate privileges.
The issue is with how BPF JIT compilers for some architectures compute branch displacements when generating machine code. This can be abused to craft anomalous machine code and execute it in the Kernel mode, where the control flow is hijacked to execute unsafe code.
I developed PoCs for x86-64 and x86-32 architectures to demonstrate shellcode execution in Kernel mode by unprivileged local users.
One of these PoCs has been shared privately with security@kernel.org to assist with fix development.
Patches to mitigate the issue for x86-64 and x86-32 architectures are available. These patches do not attempt to correct the underlying algorithm and instead assert that all computations were performed correctly, such that all unsafe inputs are rejected.
The patches were published via BPF subsystem public git repository:
- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/patch/?id=e4d4d4...
- https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git/patch/?id=26f55a...
# Discoverer
Piotr Krysiuk piotras@gmail.com
# References
CVE-2021-29154 (reserved via https://cveform.mitre.org/)