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bpf: Fix a bpf_kptr_xchg() issue with local kptr

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When reviewing local percpu kptr support, Alexei discovered a bug
wherea bpf_kptr_xchg() may succeed even if the map value kptr type and
locally allocated obj type do not match ([1]). Missed struct btf_id
comparison is the reason for the bug. This patch added such struct btf_id
comparison and will flag verification failure if types do not match.

  [1] https://lore.kernel.org/bpf/20230819002907.io3iphmnuk43xblu@macbook-pro-8.dhcp.thefacebook.com/#t

Reported-by: Alexei Starovoitov <ast@kernel.org>
Fixes: 738c96d5e2 ("bpf: Allow local kptrs to be exchanged via bpf_kptr_xchg")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20230822050053.2886960-1-yonghong.song@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Yonghong Song 2023-08-21 22:00:53 -07:00 committed by Alexei Starovoitov
parent d565183800
commit ab6c637ad0
1 changed files with 15 additions and 10 deletions
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25
kernel/bpf/verifier.c
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@ -4990,20 +4990,22 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
struct bpf_reg_state *reg, u32 regno)
{
const char *targ_name = btf_type_name(kptr_field->kptr.btf, kptr_field->kptr.btf_id);
int perm_flags = PTR_MAYBE_NULL | PTR_TRUSTED | MEM_RCU;
int perm_flags;
const char *reg_name = "";
/* Only unreferenced case accepts untrusted pointers */
if (kptr_field->type == BPF_KPTR_UNREF)
perm_flags |= PTR_UNTRUSTED;
if (btf_is_kernel(reg->btf)) {
perm_flags = PTR_MAYBE_NULL | PTR_TRUSTED | MEM_RCU;
/* Only unreferenced case accepts untrusted pointers */
if (kptr_field->type == BPF_KPTR_UNREF)
perm_flags |= PTR_UNTRUSTED;
} else {
perm_flags = PTR_MAYBE_NULL | MEM_ALLOC;
}
if (base_type(reg->type) != PTR_TO_BTF_ID || (type_flag(reg->type) & ~perm_flags))
goto bad_type;
if (!btf_is_kernel(reg->btf)) {
verbose(env, "R%d must point to kernel BTF\n", regno);
return -EINVAL;
}
/* We need to verify reg->type and reg->btf, before accessing reg->btf */
reg_name = btf_type_name(reg->btf, reg->btf_id);
@ -5016,7 +5018,7 @@ static int map_kptr_match_type(struct bpf_verifier_env *env,
if (__check_ptr_off_reg(env, reg, regno, true))
return -EACCES;
/* A full type match is needed, as BTF can be vmlinux or module BTF, and
/* A full type match is needed, as BTF can be vmlinux, module or prog BTF, and
* we also need to take into account the reg->off.
*
* We want to support cases like:
@ -7916,7 +7918,10 @@ found:
verbose(env, "verifier internal error: unimplemented handling of MEM_ALLOC\n");
return -EFAULT;
}
/* Handled by helper specific checks */
if (meta->func_id == BPF_FUNC_kptr_xchg) {
if (map_kptr_match_type(env, meta->kptr_field, reg, regno))
return -EACCES;
}
break;
case PTR_TO_BTF_ID | MEM_PERCPU:
case PTR_TO_BTF_ID | MEM_PERCPU | PTR_TRUSTED: