From f08619f060468076e4acbdc10e0713af20d60e65 Mon Sep 17 00:00:00 2001 From: Kumar Kartikeya Dwivedi Date: Sun, 19 Jul 2026 17:36:29 +0200 Subject: [PATCH] bpf: Preserve unique-field state across nested structs btf_find_struct_field() initializes a fresh seen mask for every recursive descent. Unique special fields in different levels of the same aggregate therefore do not see one another. The duplicate fields can reach btf_parse_fields(), where they trigger an invariant WARN_ON_ONCE(). A crafted user BTF can consequently trigger the warning before map creation checks capabilities. Initialize the seen mask once in btf_find_field() and pass the same pointer through struct, datasec, and nested-struct walks. This gives the entire field traversal one shared uniqueness state. Fixes: 64e8ee814819 ("bpf: look into the types of the fields of a struct type recursively.") Signed-off-by: Kumar Kartikeya Dwivedi Link: https://patch.msgid.link/20260719153634.2908692-3-memxor@gmail.com Signed-off-by: Eduard Zingerman --- kernel/bpf/btf.c | 26 ++++++++++++++------------ 1 file changed, 14 insertions(+), 12 deletions(-) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index e7d4e9ba24e2..c577f00e9d88 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -3751,7 +3751,7 @@ static int btf_repeat_fields(struct btf_field_info *info, int info_cnt, static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t, u32 field_mask, struct btf_field_info *info, int info_cnt, - u32 level); + u32 level, u32 *seen_mask); /* Find special fields in the struct type of a field. * @@ -3762,7 +3762,7 @@ static int btf_find_struct_field(const struct btf *btf, static int btf_find_nested_struct(const struct btf *btf, const struct btf_type *t, u32 off, u32 nelems, u32 field_mask, struct btf_field_info *info, - int info_cnt, u32 level) + int info_cnt, u32 level, u32 *seen_mask) { int ret, err, i; @@ -3770,7 +3770,7 @@ static int btf_find_nested_struct(const struct btf *btf, const struct btf_type * if (level >= MAX_RESOLVE_DEPTH) return -E2BIG; - ret = btf_find_struct_field(btf, t, field_mask, info, info_cnt, level); + ret = btf_find_struct_field(btf, t, field_mask, info, info_cnt, level, seen_mask); if (ret <= 0) return ret; @@ -3827,7 +3827,7 @@ static int btf_find_field_one(const struct btf *btf, if (expected_size && expected_size != sz * nelems) return 0; ret = btf_find_nested_struct(btf, var_type, off, nelems, field_mask, - &info[0], info_cnt, level); + &info[0], info_cnt, level, seen_mask); return ret; } @@ -3892,11 +3892,11 @@ static int btf_find_field_one(const struct btf *btf, static int btf_find_struct_field(const struct btf *btf, const struct btf_type *t, u32 field_mask, struct btf_field_info *info, int info_cnt, - u32 level) + u32 level, u32 *seen_mask) { int ret, idx = 0; const struct btf_member *member; - u32 i, off, seen_mask = 0; + u32 i, off; for_each_member(i, t, member) { const struct btf_type *member_type = btf_type_by_id(btf, @@ -3910,7 +3910,7 @@ static int btf_find_struct_field(const struct btf *btf, ret = btf_find_field_one(btf, t, member_type, i, off, 0, - field_mask, &seen_mask, + field_mask, seen_mask, &info[idx], info_cnt - idx, level); if (ret < 0) return ret; @@ -3921,11 +3921,11 @@ static int btf_find_struct_field(const struct btf *btf, static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t, u32 field_mask, struct btf_field_info *info, - int info_cnt, u32 level) + int info_cnt, u32 level, u32 *seen_mask) { int ret, idx = 0; const struct btf_var_secinfo *vsi; - u32 i, off, seen_mask = 0; + u32 i, off; for_each_vsi(i, t, vsi) { const struct btf_type *var = btf_type_by_id(btf, vsi->type); @@ -3933,7 +3933,7 @@ static int btf_find_datasec_var(const struct btf *btf, const struct btf_type *t, off = vsi->offset; ret = btf_find_field_one(btf, var, var_type, -1, off, vsi->size, - field_mask, &seen_mask, + field_mask, seen_mask, &info[idx], info_cnt - idx, level); if (ret < 0) @@ -3947,10 +3947,12 @@ static int btf_find_field(const struct btf *btf, const struct btf_type *t, u32 field_mask, struct btf_field_info *info, int info_cnt) { + u32 seen_mask = 0; + if (__btf_type_is_struct(t)) - return btf_find_struct_field(btf, t, field_mask, info, info_cnt, 0); + return btf_find_struct_field(btf, t, field_mask, info, info_cnt, 0, &seen_mask); else if (btf_type_is_datasec(t)) - return btf_find_datasec_var(btf, t, field_mask, info, info_cnt, 0); + return btf_find_datasec_var(btf, t, field_mask, info, info_cnt, 0, &seen_mask); return -EINVAL; }