bpf: Reject sleepable kprobe_multi programs at attach time

commit eb7024bfcc5f68ed11ed9dd4891a3073c15f04a8 upstream.

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.

BUG=b/508877543
TEST=presubmit
RELEASE_NOTE=Fixed CVE-2026-43010 in the Linux kernel.

cos-patch: security-moderate
Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
Change-Id: I5086919000d3c276ac6aad27a8945f5acccf83fb
Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Acked-by: Leon Hwang <leon.hwang@linux.dev>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20260401191126.440683-1-varunrmallya@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kernel CVE Triage Automation <cloud-image-kernel-cve-triage-automation@prod.google.com>
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/167764
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Reviewed-by: He Gao <hegao@google.com>