[PATCH bpf-next v4 0/2] Reject sleepable kprobe_multi programs at attach time

[Varun R Mallya <varunrmallya@gmail.com>]

These patches fix an issue where sleepable kprobe_multi programs
were allowed to attach, leading to "sleeping function called from invalid
context" splats.

Because kprobe.multi programs run in atomic/RCU context, they cannot
sleep. However, `bpf_kprobe_multi_link_attach()` previously lacked
validation for the `prog->sleepable` flag. This allowed sleepable
helpers, such as `bpf_copy_from_user()`, to be invoked from an invalid
non-sleepable context.

This series addresses the issue by:
1. Rejecting sleepable kprobe_multi programs early in
   `bpf_kprobe_multi_link_attach()` by returning -EINVAL.
2. Adding selftests to explicitly verify that attaching a sleepable
   kprobe_multi program is rejected by the kernel.

P.S: The first of these two commits has been applied to the bpf tree.

Changes:
v1->v2:
- v1: https://lore.kernel.org/bpf/20260401134921.362148-1-varunrmallya@gmail.com/
- Defective selftest added
v2->v3:
- v2: https://lore.kernel.org/bpf/CAP01T74YgnKop-dgwBToOcfg4_D44t1wUBopFYPMquirCmaLfg@mail.gmail.com/
- Selftest separated from change into different commit.
v3->v4:
- v3: https://lore.kernel.org/bpf/20260401191126.440683-1-varunrmallya@gmail.com/
- Selftest moved to test_attach_api_fails.
- Changed attachment symbol to bpf_fentry_test1 for stability.
- Changes suggested by Leon implemented.

Varun R Mallya (2):
  bpf: Reject sleepable kprobe_multi programs at attach time
  selftests/bpf: Add test to ensure kprobe_multi is not sleepable

 kernel/trace/bpf_trace.c                      |  4 +
 .../bpf/prog_tests/kprobe_multi_test.c        | 78 ++++++++++++++++++-
 .../bpf/progs/kprobe_multi_sleepable.c        | 25 ++++++
 3 files changed, 106 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c

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2.53.0