| Message ID | 20220301065745.1634848-4-memxor@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | Fixes for bad PTR_TO_BTF_ID offset | expand |
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a641e61767b4..9f12a343bb6e 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3984,6 +3984,12 @@ 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);
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. Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> --- kernel/bpf/verifier.c | 6 ++++++ 1 file changed, 6 insertions(+)