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/[email protected]/ v2 -> v3: * Use btf_is_kernel() instead of passing 'tgt_prog'. (per Andrii) * v2: https://lore.kernel.org/bpf/[email protected]/ v1 -> v2: * Drop redundant 'prog->sleepable' check. (per Viktor) * Collect Acked-by from Viktor, Thanks. * v1: https://lore.kernel.org/bpf/[email protected]/ 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 -- 2.55.0
