[PATCH bpf-next v4 0/2] bpf: Fix sleepable check for tracing/lsm prog

[Leon Hwang]

When CONFIG_FUNCTION_ERROR_INJECTION is disabled, a sleepable tracing prog
is allowed to attach to '__x64_'-alike prefix symbols.

It is because the verifier does not verify whether the symbol is a kernel
function or a bpf prog. That said, a sleepable tracing prog is allowed to
attach to a bpf prog target whose name has '__x64_'-alike prefix.

For example, a sleepable fentry prog attaches to a '__x64_sys_nop' XDP
prog, and copies buffer from a user pointer with bpf_copy_from_user()
helper. After attaching the XDP prog to lo interface, the kernel BUG
could be triggered by 'ping -c 1 -W 1 127.0.0.1':

[    3.460756] BUG: sleeping function called from invalid context at kernel/bpf/trampoline.c:1324

Similar issue could be applied to lsm prog, when the
prog->aux->attach_btf_id is in the LSM allowing list but the attach_btf is
a malicious bpf prog's btf.

Fix it by disallowing sleepable tracing/lsm prog always when its target
btf is not kernel's btf.

Changes:
v3 -> v4:
* Add Fixes tag for sleepable LSM case.
* Move btf check outside of 'switch (prog->type)'. (per Andrii)
* v3: https://lore.kernel.org/bpf/20260804145710.43062-1-leon.hwang@xxxxxxxxx/

v2 -> v3:
* Use btf_is_kernel() instead of passing 'tgt_prog'. (per Andrii)
* v2: https://lore.kernel.org/bpf/20260725132624.78373-1-leon.hwang@xxxxxxxxx/

v1 -> v2:
* Drop redundant 'prog->sleepable' check. (per Viktor)
* Collect Acked-by from Viktor, Thanks.
* v1: https://lore.kernel.org/bpf/20260724141422.10463-1-leon.hwang@xxxxxxxxx/

Leon Hwang (2):
  bpf: Fix sleepable check for tracing/lsm prog
  selftests/bpf: Verify rejection of sleepable tracing prog

 kernel/bpf/verifier.c                         |  3 +
 .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  | 57 +++++++++++++++++++
 .../selftests/bpf/progs/fentry_sleepable.c    | 18 ++++++
 tools/testing/selftests/bpf/progs/xdp_dummy.c |  6 ++
 4 files changed, 84 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/fentry_sleepable.c

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2.55.0