diff options
| author | Kumar Kartikeya Dwivedi <memxor@gmail.com> | 2022-03-05 04:16:40 +0530 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2022-03-05 15:29:35 -0800 |
| commit | e1fad0ff46b32819d30cb487f1d39ba24e515843 (patch) | |
| tree | 6758622bae951cd13be976438a4c7695aa4e6f7a /kernel | |
| parent | 655efe5089f077485eec848272bd7e26b1a5a735 (diff) | |
bpf: Disallow negative offset in check_ptr_off_reg
check_ptr_off_reg only allows fixed offset to be set for PTR_TO_BTF_ID,
where reg->off < 0 doesn't make sense. This would shift the pointer
backwards, and fails later in btf_struct_ids_match or btf_struct_walk
due to out of bounds access (since offset is interpreted as unsigned).
Improve the verifier by rejecting this case by using a better error
message for BPF helpers and kfunc, by putting a check inside the
check_func_arg_reg_off function.
Also, update existing verifier selftests to work with new error string.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220304224645.3677453-4-memxor@gmail.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/bpf/verifier.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index e37eb6020253..455b4ab69e47 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3990,6 +3990,12 @@ static int __check_ptr_off_reg(struct bpf_verifier_env *env, * is only allowed in its original, unmodified form. */ + if (reg->off < 0) { + verbose(env, "negative offset %s ptr R%d off=%d disallowed\n", + reg_type_str(env, reg->type), regno, reg->off); + return -EACCES; + } + if (!fixed_off_ok && reg->off) { verbose(env, "dereference of modified %s ptr R%d off=%d disallowed\n", reg_type_str(env, reg->type), regno, reg->off); |