bpf: Reject sleepable kprobe_multi programs at attach time

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

bpf: Reject sleepable kprobe_multi programs at attach time

kprobe.multi programs run in atomic/RCU context and cannot sleep.

However, bpf_kprobe_multi_link_attach() did not validate whether the

program being attached had the sleepable flag set, allowing sleepable

helpers such as bpf_copy_from_user() to be invoked from a non-sleepable

context.

This causes a "sleeping function called from invalid context" splat:

BUG: sleeping function called from invalid context at ./include/linux/uaccess.h:169

in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1787, name: sudo

preempt_count: 1, expected: 0

RCU nest depth: 2, expected: 0

Fix this by rejecting sleepable programs early in

bpf_kprobe_multi_link_attach(), before any further processing.