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 Fix it by disallowing sleepable tracing prog always when its target is bpf prog. Leon Hwang (2): bpf: Fix sleepable check for tracing prog selftests/bpf: Verify rejection of sleepable tracing prog kernel/bpf/verifier.c | 9 ++- .../selftests/bpf/prog_tests/fexit_bpf2bpf.c | 57 +++++++++++++++++++ .../selftests/bpf/progs/fentry_sleepable.c | 19 +++++++ tools/testing/selftests/bpf/progs/xdp_dummy.c | 6 ++ 4 files changed, 88 insertions(+), 3 deletions(-) create mode 100644 tools/testing/selftests/bpf/progs/fentry_sleepable.c -- 2.55.0
