Re: [PATCH bpf-next 4/5] btf: fix bug with resolving STRUCT/UNION into corresponding FWD
From: Song Liu <hidden>
Date: 2019-02-28 18:29:20
Also in:
bpf
On Wed, Feb 27, 2019 at 2:48 PM Andrii Nakryiko [off-list ref] wrote:
When checking available canonical candidates for struct/union algorithm
utilizes btf_dedup_is_equiv to determine if candidate is suitable. This
check is not enough when candidate is corresponding FWD for that
struct/union, because according to equivalence logic they are
equivalent. When it so happens that FWD and STRUCT/UNION end in hashing
to the same bucket, it's possible to create remapping loop from FWD to
STRUCT and STRUCT to same FWD, which will cause btf_dedup() to loop
forever.
This patch fixes the issue by additionally checking that type and
canonical candidate are strictly equal (utilizing btf_equal_struct).
Fixes: d5caef5b5655 ("btf: add BTF types deduplication algorithm")
Reported-by: Arnaldo Carvalho de Melo <redacted>
Signed-off-by: Andrii Nakryiko <redacted>Acked-by: Song Liu <redacted>
quoted hunk ↗ jump to hunk
--- tools/lib/bpf/btf.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index 6bbb710216e6..53db26d158c9 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c@@ -2255,7 +2255,7 @@ static void btf_dedup_merge_hypot_map(struct btf_dedup *d) static int btf_dedup_struct_type(struct btf_dedup *d, __u32 type_id) { struct btf_dedup_node *cand_node; - struct btf_type *t; + struct btf_type *cand_type, *t; /* if we don't find equivalent type, then we are canonical */ __u32 new_id = type_id; __u16 kind;@@ -2275,6 +2275,10 @@ static int btf_dedup_struct_type(struct btf_dedup *d, __u32 type_id) for_each_dedup_cand(d, h, cand_node) { int eq; + cand_type = d->btf->types[cand_node->type_id]; + if (!btf_equal_struct(t, cand_type)) + continue; + btf_dedup_clear_hypot_map(d); eq = btf_dedup_is_equiv(d, type_id, cand_node->type_id); if (eq < 0) --2.17.1