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

bpf: Fix a kernel verifier crash in stacksafe()

Daniel Hodges reported a kernel verifier crash when playing with sched-ext.
Further investigation shows that the crash is due to invalid memory access
in stacksafe(). More specifically, it is the following code:

if (exact != NOT_EXACT &&
    old->stack[spi].slot_type[i % BPF_REG_SIZE] !=
    cur->stack[spi].slot_type[i % BPF_REG_SIZE])
        return false;

The 'i' iterates old->allocated_stack.
If cur->allocated_stack < old->allocated_stack the out-of-bound
access will happen.

To fix the issue add 'i >= cur->allocated_stack' check such that if
the condition is true, stacksafe() should fail. Otherwise,
cur->stack[spi].slot_type[i % BPF_REG_SIZE] memory access is legal.

References

• https://nvd.nist.gov/vuln/detail/CVE-2024-45020
• https://git.kernel.org/stable/c/6e3987ac310c74bb4dd6a2fa8e46702fe505fb2b
• https://git.kernel.org/stable/c/7cad3174cc79519bf5f6c4441780264416822c08
• https://git.kernel.org/stable/c/bed2eb964c70b780fb55925892a74f26cb590b25