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| author | Andrii Nakryiko <andriin@fb.com> | 2019-02-28 15:31:24 -0800 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2019-03-01 01:31:48 +0100 |
| commit | 91097fbee4c025ac72f91ae41feba3a822cc1316 (patch) | |
| tree | 3e1fb0359be566403120bd51df1e921c3b217d83 | |
| parent | 51edf5f6e015c48b62e24ab2fbcad8885ca1c74e (diff) | |
| download | linux-91097fbee4c025ac72f91ae41feba3a822cc1316.tar.gz linux-91097fbee4c025ac72f91ae41feba3a822cc1316.tar.bz2 linux-91097fbee4c025ac72f91ae41feba3a822cc1316.zip | |
btf: fix bug with resolving STRUCT/UNION into corresponding FWD
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 <acme@redhat.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
| -rw-r--r-- | tools/lib/bpf/btf.c | 20 |
1 files changed, 17 insertions, 3 deletions
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c index 820f7fc8ebcc..1b8d8cdd3575 100644 --- a/tools/lib/bpf/btf.c +++ b/tools/lib/bpf/btf.c @@ -1663,7 +1663,7 @@ static __u32 btf_hash_struct(struct btf_type *t) * IDs. This check is performed during type graph equivalence check and * referenced types equivalence is checked separately. */ -static bool btf_equal_struct(struct btf_type *t1, struct btf_type *t2) +static bool btf_shallow_equal_struct(struct btf_type *t1, struct btf_type *t2) { struct btf_member *m1, *m2; __u16 vlen; @@ -2124,7 +2124,7 @@ static int btf_dedup_is_equiv(struct btf_dedup *d, __u32 cand_id, struct btf_member *cand_m, *canon_m; __u16 vlen; - if (!btf_equal_struct(cand_type, canon_type)) + if (!btf_shallow_equal_struct(cand_type, canon_type)) return 0; vlen = BTF_INFO_VLEN(cand_type->info); cand_m = (struct btf_member *)(cand_type + 1); @@ -2265,7 +2265,7 @@ 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; @@ -2285,6 +2285,20 @@ static int btf_dedup_struct_type(struct btf_dedup *d, __u32 type_id) for_each_dedup_cand(d, h, cand_node) { int eq; + /* + * Even though btf_dedup_is_equiv() checks for + * btf_shallow_equal_struct() internally when checking two + * structs (unions) for equivalence, we need to guard here + * from picking matching FWD type as a dedup candidate. + * This can happen due to hash collision. In such case just + * relying on btf_dedup_is_equiv() would lead to potentially + * creating a loop (FWD -> STRUCT and STRUCT -> FWD), because + * FWD and compatible STRUCT/UNION are considered equivalent. + */ + cand_type = d->btf->types[cand_node->type_id]; + if (!btf_shallow_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) |