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* [PATCH bpf] libbpf: add null pointer check in bpf_object__init_user_btf_maps()
@ 2020-03-12 14:03 Quentin Monnet
  2020-03-12 14:22 ` Michal Rostecki
  2020-03-12 15:37 ` Daniel Borkmann
  0 siblings, 2 replies; 7+ messages in thread
From: Quentin Monnet @ 2020-03-12 14:03 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann
  Cc: bpf, netdev, Quentin Monnet, Andrii Nakryiko, Michal Rostecki

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@fb.com>
Reported-by: Michal Rostecki <mrostecki@opensuse.org>
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
---
 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");
+		return -EINVAL;
+	}
 	nr_types = btf__get_nr_types(obj->btf);
 	for (i = 1; i <= nr_types; i++) {
 		t = btf__type_by_id(obj->btf, i);
-- 
2.20.1


^ permalink raw reply related	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2020-03-12 18:35 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-12 14:03 [PATCH bpf] libbpf: add null pointer check in bpf_object__init_user_btf_maps() Quentin Monnet
2020-03-12 14:22 ` Michal Rostecki
2020-03-12 15:37 ` Daniel Borkmann
2020-03-12 16:50   ` Quentin Monnet
2020-03-12 17:54   ` Andrii Nakryiko
2020-03-12 18:21     ` Daniel Borkmann
2020-03-12 18:34       ` Quentin Monnet

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