On 3/12/20 6:54 PM, Andrii Nakryiko wrote:
On Thu, Mar 12, 2020 at 8:38 AM Daniel Borkmann <daniel@xxxxxxxxxxxxx> wrote:
On 3/12/20 3:03 PM, Quentin Monnet wrote:
When compiling bpftool with clang 7, after the addition of its recent
"bpftool prog profile" feature, Michal reported a segfault. This
occurred while the build process was attempting to generate the
skeleton needed for the profiling program, with the following command:
./_bpftool gen skeleton skeleton/profiler.bpf.o > profiler.skel.h
Tracing the error showed that bpf_object__init_user_btf_maps() does no
verification on obj->btf before passing it to btf__get_nr_types(), where
btf is dereferenced. Libbpf considers BTF information should be here
because of the presence of a ".maps" section in the object file (hence
the check on "obj->efile.btf_maps_shndx < 0" fails and we do not exit
from the function early), but it was unable to load BTF info as there is
no .BTF section.
Add a null pointer check and error out if the pointer is null. The final
bpftool executable still fails to build, but at least we have a proper
error and no more segfault.
Fixes: abd29c931459 ("libbpf: allow specifying map definitions using BTF")
Cc: Andrii Nakryiko <andriin@xxxxxx>
Reported-by: Michal Rostecki <mrostecki@xxxxxxxxxxxx>
Signed-off-by: Quentin Monnet <quentin@xxxxxxxxxxxxx>
Applied to bpf-next, thanks! Note ...
I don't think this is the right fix. The problem was in my
5327644614a1 ("libbpf: Relax check whether BTF is mandatory") commit.
I've removed "mandatory" status of BTF if .maps is present. But that's
not right. We have the need for BTF at two levels: for libbpf itself
and for kernel, those are overlapping, but not exactly the same. BTF
is needed for libbpf when .maps, .struct_ops and externs are present.
But kernel needs it only for when .struct_ops are present. Right now
those checks are conflated together. Proper fix would be to separate
them. Can we please undo this patch? I'll post a proper fix shortly.
Ok, please send a proper fix for 5327644614a1 then. Tossed off the tree.
