From: Jakub Sitnicki <jakub@cloudflare.com>
To: bot+bpf-ci@kernel.org
Cc: bpf@vger.kernel.org, davem@davemloft.net, edumazet@google.com,
kuba@kernel.org, pabeni@redhat.com, horms@kernel.org,
martin.lau@linux.dev, daniel@iogearbox.net,
john.fastabend@gmail.com, sdf@fomichev.me, ast@kernel.org,
andrii@kernel.org, eddyz87@gmail.com, song@kernel.org,
yonghong.song@linux.dev, kpsingh@kernel.org, haoluo@google.com,
jolsa@kernel.org, arthur@arthurfabre.com, hawk@kernel.org,
netdev@vger.kernel.org, kernel-team@cloudflare.com,
martin.lau@kernel.org, clm@meta.com, ihor.solodrai@linux.dev
Subject: Re: [PATCH bpf-next v4 07/16] bpf: Make bpf_skb_adjust_room metadata-safe
Date: Mon, 10 Nov 2025 13:17:48 +0100 [thread overview]
Message-ID: <87bjlaf5eb.fsf@cloudflare.com> (raw)
In-Reply-To: <9b3ca8c01aac5510f1ff8738b3856e5e2bbe43075333c27642eb69a6847a50ef@mail.kernel.org> (bot's message of "Wed, 5 Nov 2025 20:42:03 +0000 (UTC)")
On Wed, Nov 05, 2025 at 08:42 PM GMT, bot+bpf-ci@kernel.org wrote:
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 96714eab9..370ddc61b 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -3260,11 +3260,11 @@ static void bpf_skb_change_protocol(struct sk_buff *skb, u16 proto)
>>
>> static int bpf_skb_generic_push(struct sk_buff *skb, u32 off, u32 len)
>> {
>> - /* Caller already did skb_cow() with len as headroom,
>> + /* Caller already did skb_cow() with meta_len+len as headroom,
>> * so no need to do it here.
>> */
>> skb_push(skb, len);
>> - memmove(skb->data, skb->data + len, off);
>> + skb_postpush_data_move(skb, len, off);
>> memset(skb->data + off, 0, len);
>
> The comment update says callers provide meta_len+len as headroom, but
> is this true for all callers?
>
> bpf_skb_proto_4_to_6() calls skb_cow(skb, len_diff) then calls
> bpf_skb_net_hdr_push()->bpf_skb_generic_push(). Similarly,
> bpf_lwt_seg6_adjust_srh() calls skb_cow_head(skb, len) then calls
> bpf_skb_net_hdr_push()->bpf_skb_generic_push().
>
> Neither accounts for meta_len in their headroom calculation. When
> skb_postpush_data_move()->skb_data_move() runs, if meta_len >
> skb_headroom(skb) after the push, the metadata gets silently cleared
> (see the WARN_ON_ONCE check in skb_data_move() at skbuff.h).
>
> Can the metadata be lost when these functions are called on skbs with
> metadata?
bpf_skb_proto_4_to_6() is handled by the next patch (8/16).
LWT and other encap facilities are out of scope for this series.
bpf_lwt_seg6_adjust_srh() is on my todo list.
[...]
next prev parent reply other threads:[~2025-11-10 12:17 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-05 20:19 [PATCH bpf-next v4 00/16] Make TC BPF helpers preserve skb metadata Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 01/16] net: Helper to move packet data and metadata after skb_push/pull Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 02/16] net: Preserve metadata on pskb_expand_head Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 03/16] bpf: Unclone skb head on bpf_dynptr_write to skb metadata Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 04/16] vlan: Make vlan_remove_tag return nothing Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 05/16] bpf: Make bpf_skb_vlan_pop helper metadata-safe Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 06/16] bpf: Make bpf_skb_vlan_push " Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 07/16] bpf: Make bpf_skb_adjust_room metadata-safe Jakub Sitnicki
2025-11-05 20:42 ` bot+bpf-ci
2025-11-10 12:17 ` Jakub Sitnicki [this message]
2025-11-05 20:19 ` [PATCH bpf-next v4 08/16] bpf: Make bpf_skb_change_proto helper metadata-safe Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 09/16] bpf: Make bpf_skb_change_head " Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 10/16] selftests/bpf: Verify skb metadata in BPF instead of userspace Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 11/16] selftests/bpf: Dump skb metadata on verification failure Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 12/16] selftests/bpf: Expect unclone to preserve skb metadata Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 13/16] selftests/bpf: Cover skb metadata access after vlan push/pop helper Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 14/16] selftests/bpf: Cover skb metadata access after bpf_skb_adjust_room Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 15/16] selftests/bpf: Cover skb metadata access after change_head/tail helper Jakub Sitnicki
2025-11-05 20:19 ` [PATCH bpf-next v4 16/16] selftests/bpf: Cover skb metadata access after bpf_skb_change_proto Jakub Sitnicki
2025-11-10 19:30 ` [PATCH bpf-next v4 00/16] Make TC BPF helpers preserve skb metadata patchwork-bot+netdevbpf
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