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bpf: Fix modifier skipping logic

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Fix the way modifiers are skipped while walking pointers. Otherwise second
level dereferences of 'const struct foo *' will be rejected by the verifier.

Fixes: 9e15db6613 ("bpf: Implement accurate raw_tp context access via BTF")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200201000314.261392-1-ast@kernel.org
This commit is contained in:
Alexei Starovoitov 2020-01-31 16:03:14 -08:00 committed by Daniel Borkmann
parent a525b0881d
commit 257af63d7f
1 changed files with 3 additions and 5 deletions
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8
kernel/bpf/btf.c
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@ -3931,6 +3931,7 @@ int btf_struct_access(struct bpf_verifier_log *log,
if (btf_type_is_ptr(mtype)) {
const struct btf_type *stype;
u32 id;
if (msize != size || off != moff) {
bpf_log(log,
@ -3939,12 +3940,9 @@ int btf_struct_access(struct bpf_verifier_log *log,
return -EACCES;
}
stype = btf_type_by_id(btf_vmlinux, mtype->type);
/* skip modifiers */
while (btf_type_is_modifier(stype))
stype = btf_type_by_id(btf_vmlinux, stype->type);
stype = btf_type_skip_modifiers(btf_vmlinux, mtype->type, &id);
if (btf_type_is_struct(stype)) {
*next_btf_id = mtype->type;
*next_btf_id = id;
return PTR_TO_BTF_ID;
}
}