netdev - Re: [PATCH net] net: test tailroom before appending to linear skb

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Date:   Thu, 17 May 2018 13:03:32 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net] net: test tailroom before appending to linear skb

On Thu, May 17, 2018 at 12:44 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
> On 05/17/2018 08:54 AM, Willem de Bruijn wrote:
>> From: Willem de Bruijn <willemb@...gle.com>
>>
>> Device features may change during transmission. In particular with
>> corking, a device may toggle scatter-gather in between allocating
>> and writing to an skb.
>>
>> Do not unconditionally assume that !NETIF_F_SG at write time implies
>> that the same held at alloc time and thus the skb has sufficient
>> tailroom.
>>
>> This issue predates git history.
>>
>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>> Reported-by: Eric Dumazet <edumazet@...gle.com>
>> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
>> ---
>>  net/ipv4/ip_output.c  | 3 ++-
>>  net/ipv6/ip6_output.c | 3 ++-
>>  2 files changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
>> index 83c73bab2c3d..c15204ec2eb0 100644
>> --- a/net/ipv4/ip_output.c
>> +++ b/net/ipv4/ip_output.c
>> @@ -1045,7 +1045,8 @@ static int __ip_append_data(struct sock *sk,
>>               if (copy > length)
>>                       copy = length;
>>
>> -             if (!(rt->dst.dev->features&NETIF_F_SG)) {
>> +             if (!(rt->dst.dev->features&NETIF_F_SG) &&
>> +                 skb_tailroom(skb) > copy) {
>
> On second thought, maybe use >= for the test ?

Ai, yes of course. Will send a v2.