| Message ID | 20171122183256.7219-3-g.borello@gmail.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | bpf: fix semantics issues with helpers receiving NULL arguments | expand |
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index a5580c670866..728909f7951c 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -78,16 +78,12 @@ EXPORT_SYMBOL_GPL(trace_call_bpf); BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr) { - int ret = 0; - - if (unlikely(size == 0)) - goto out; + int ret; ret = probe_kernel_read(dst, unsafe_ptr, size); if (unlikely(ret < 0)) memset(dst, 0, size); - out: return ret; }
Commit 9c019e2bc4b2 ("bpf: change helper bpf_probe_read arg2 type to ARG_CONST_SIZE_OR_ZERO") changed arg2 type to ARG_CONST_SIZE_OR_ZERO to simplify writing bpf programs by taking advantage of the new semantics introduced for ARG_CONST_SIZE_OR_ZERO which allows <!NULL, 0> arguments. In order to prevent the helper from actually passing a NULL pointer to probe_kernel_read, which can happen when <NULL, 0> is passed to the helper, the commit also introduced an explicit check against size == 0. After the recent introduction of the ARG_PTR_TO_MEM_OR_NULL type, bpf_probe_read can not receive a pair of <NULL, 0> arguments anymore, thus the check is not needed anymore and can be removed, since probe_kernel_read can correctly handle a <!NULL, 0> call. This also fixes the semantics of the helper before it gets officially released and bpf programs start relying on this check. Fixes: 9c019e2bc4b2 ("bpf: change helper bpf_probe_read arg2 type to ARG_CONST_SIZE_OR_ZERO") Signed-off-by: Gianluca Borello <g.borello@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Yonghong Song <yhs@fb.com> --- kernel/trace/bpf_trace.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) -- 2.14.1