netdev - Re: [PATCH bpf-next v1] bpf, lpm: fix lookup bug in map_delete

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Date:   Fri, 22 Feb 2019 14:14:55 +0100
From:   Alban Crequy <alban@...volk.io>
To:     Martin Lau <kafai@...com>
Cc:     Alban Crequy <alban.crequy@...il.com>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iago@...volk.io" <iago@...volk.io>,
        Craig Gallek <kraig@...gle.com>
Subject: Re: [PATCH bpf-next v1] bpf, lpm: fix lookup bug in map_delete_elem

On Thu, Feb 21, 2019 at 11:24 PM Martin Lau <kafai@...com> wrote:
>
> On Thu, Feb 21, 2019 at 05:39:26PM +0100, Alban Crequy wrote:
> > From: Alban Crequy <alban@...volk.io>
> >
> > trie_delete_elem() was deleting an entry even though it was not matching
> > if the prefixlen was correct. This patch adds a check on matchlen.
> >
> > Reproducer:
> >
> > $ sudo bpftool map create /sys/fs/bpf/mylpm type lpm_trie key 8 value 1 entries 128 name mylpm flags 1
> > $ sudo bpftool map update pinned /sys/fs/bpf/mylpm key hex 10 00 00 00 aa bb cc dd value hex 01
> > $ sudo bpftool map dump pinned /sys/fs/bpf/mylpm
> > key: 10 00 00 00 aa bb cc dd  value: 01
> > Found 1 element
> > $ sudo bpftool map delete pinned /sys/fs/bpf/mylpm key hex 10 00 00 00 ff ff ff ff
> > $ echo $?
> > 0
> > $ sudo bpftool map dump pinned /sys/fs/bpf/mylpm
> > Found 0 elements
> The change makes sense to me.  Can you add this reproducer to
> tools/testing/selftests/bpf/test_lpm_map.c?
>
> Bug fix should be for the "bpf" tree instead of "bpf-next"
> Fixes tag is also required, like
>
> Fixes: e454cf595853 ("bpf: Implement map_delete_elem for BPF_MAP_TYPE_LPM_TRIE")
> Cc: Craig Gallek <kraig@...gle.com>

Thanks! I'll send a v2 shortly with the selftest and the tags, based
on "bpf" tree.

Cheers,
Alban

> > Signed-off-by: Alban Crequy <alban@...volk.io>
> > ---
> >  kernel/bpf/lpm_trie.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
> > index abf1002080df..93a5cbbde421 100644
> > --- a/kernel/bpf/lpm_trie.c
> > +++ b/kernel/bpf/lpm_trie.c
> > @@ -471,6 +471,7 @@ static int trie_delete_elem(struct bpf_map *map, void *_key)
> >       }
> >
> >       if (!node || node->prefixlen != key->prefixlen ||
> > +         node->prefixlen != matchlen ||
> >           (node->flags & LPM_TREE_NODE_FLAG_IM)) {
> >               ret = -ENOENT;
> >               goto out;
> > --
> > 2.20.1
> >