bpf: Fix a kernel verifier crash in stacksafe()

Vulnerability Description

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://git.kernel.org/stable/c/7cad3174cc79519bf5f6c4441780264416822c08
• https://git.kernel.org/stable/c/6e3987ac310c74bb4dd6a2fa8e46702fe505fb2b
• https://git.kernel.org/stable/c/bed2eb964c70b780fb55925892a74f26cb590b25