Subject: Re: [PATCH net-next v2 3/6] net: dcb: add new rewrite table

From: Petr Machata <[email-masked]>
Date: Thu, 19 Jan 2023 10:38:03 +0100

Dan Carpenter <[email-masked]> writes:

> On Wed, Jan 18, 2023 at 11:54:23AM +0100, Petr Machata wrote:
>> > +
>> > +	spin_lock_bh(&dcb_lock);
>> > +	list_for_each_entry(itr, &dcb_rewr_list, list) {
>> > +		if (itr->ifindex == netdev->ifindex) {
>> > +			enum ieee_attrs_app type =
>> > +				dcbnl_app_attr_type_get(itr->app.selector);
>> > +			err = nla_put(skb, type, sizeof(itr->app), &itr->app);
>> > +			if (err) {
>> > +				spin_unlock_bh(&dcb_lock);
>> 
>> This should cancel the nest started above.
>> 
>
> If you see a bug like this, you may as well ask Julia or me to add a
> static checker warning for it.  We're both already on the CC list but we
> might not be following the conversation closely...

I'll try to remember next time.

> In Smatch, I thought it would be easy but it turned out I need to add
> a hack around to change the second nla_nest_start_noflag() from unknown
> to valid pointer.
>
> diff --git a/check_unwind.c b/check_unwind.c
> index a397afd2346b..3128476cbeb6 100644
> --- a/check_unwind.c
> +++ b/check_unwind.c
> @@ -94,6 +94,11 @@ static struct ref_func_info func_table[] = {
>  
>  	{ "ieee80211_alloc_hw", ALLOC,  -1, "$", &valid_ptr_min_sval, &valid_ptr_max_sval },
>  	{ "ieee80211_free_hw",  RELEASE, 0, "$" },
> +
> +	{ "nla_nest_start_noflag", ALLOC, 0, "$", &valid_ptr_min_sval, &valid_ptr_max_sval },
> +	{ "nla_nest_start", ALLOC, 0, "$", &valid_ptr_min_sval, &valid_ptr_max_sval },
> +	{ "nla_nest_end", RELEASE, 0, "$" },
> +	{ "nla_nest_cancel", RELEASE, 0, "$" },
>  };
>  
>  static struct smatch_state *unmatched_state(struct sm_state *sm)
> diff --git a/smatch_data/db/kernel.return_fixes b/smatch_data/db/kernel.return_fixes
> index fa4ed4ba5f0f..4782c5e10cdb 100644
> --- a/smatch_data/db/kernel.return_fixes
> +++ b/smatch_data/db/kernel.return_fixes
> @@ -90,3 +90,4 @@ dma_resv_wait_timeout s64min-(-1),1-s64max 1-s64max[<=$3]
>  mmc_io_rw_direct_host s32min-(-1),1-s32max (-4095)-(-1)
>  ad3552r_transfer s32min-(-1),1-s32max (-4095)-(-1)
>  adin1110_read_reg s32min-(-1),1-s32max (-4095)-(-1)
> +nla_nest_start_noflag 0-u64max 4096-ptr_max
>
> Unfortunately, there is something weird going on and only my unreleased
> version of Smatch finds the bug:
>
> net/dcb/dcbnl.c:1306 dcbnl_ieee_fill() warn: 'skb' from nla_nest_start_noflag() not released on lines: 1160,1171,1184,1197,1207,1217,1222,1232,1257.
> net/dcb/dcbnl.c:1502 dcbnl_cee_fill() warn: 'skb' from nla_nest_start_noflag() not released on lines: 1502.

Looking at a couple of those, yeah, it looks legit. Those are missing
the cancel on error returns.

> I have been working on that check recently...  Both the released and
> unreleased versions of Smatch have the following complaints:
>
> net/dcb/dcbnl.c:400 dcbnl_getnumtcs() warn: 'skb' from nla_nest_start_noflag() not released on lines: 396.
> net/dcb/dcbnl.c:1061 dcbnl_build_peer_app() warn: 'skb' from nla_nest_start_noflag() not released on lines: 1061.
> net/dcb/dcbnl.c:1359 dcbnl_cee_pg_fill() warn: 'skb' from nla_nest_start_noflag() not released on lines: 1324,1342.

Likewise. Strange that each version reports a different subset. Or is
that just selective quoting?