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

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Date:   Thu, 21 Feb 2019 22:23:57 +0000
From:   Martin Lau <kafai@...com>
To:     Alban Crequy <alban.crequy@...il.com>
CC:     "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>,
        "alban@...volk.io" <alban@...volk.io>,
        "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 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>

> 
> 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
>