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 ...
---
tools/lib/bpf/libbpf.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 223be01dc466..19c0c40e8a80 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -2140,6 +2140,10 @@ static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
return -EINVAL;
}
+ if (!obj->btf) {
+ pr_warn("failed to retrieve BTF for map");
I've added a '\n' here, otherwise it looks like:
[...]
LINK _bpftool
CLANG skeleton/profiler.bpf.o
GEN profiler.skel.h
libbpf: failed to retrieve BTF for mapError: failed to open BPF object file: 0
Makefile:129: recipe for target 'profiler.skel.h' failed
Fixed version:
LINK _bpftool
GEN profiler.skel.h
libbpf: failed to retrieve BTF for map
Error: failed to open BPF object file: 0
Makefile:129: recipe for target 'profiler.skel.h' failed
Thanks,
Daniel
