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SubjectRe: [PATCH] net: ipv6: fix invalid alloclen in __ip6_append_data
Hi David,
On 3/7/22 18:58, David Laight wrote:
>> diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
>> index 4788f6b37053..622345af323e 100644
>> --- a/net/ipv6/ip6_output.c
>> +++ b/net/ipv6/ip6_output.c
>> @@ -1629,6 +1629,13 @@ static int __ip6_append_data(struct sock *sk,
>> err = -EINVAL;
>> goto error;
>> }
>> + if (unlikely(alloclen < fraglen)) {
>> + if (printk_ratelimit())
>> + pr_warn("%s: wrong alloclen: %d, fraglen: %d",
>> + __func__, alloclen, fraglen);
>> + alloclen = fraglen;
>> + }
>> +
> Except that is a valid case, see a few lines higher:
>
> alloclen = min_t(int, fraglen, MAX_HEADER);
> pagedlen = fraglen - alloclen;
>
> You need to report the input values that cause the problem later on.

OK, but in this case it falls into the first if block:
https://elixir.bootlin.com/linux/v5.17-rc7/source/net/ipv6/ip6_output.c#L1606
where alloclen is assigned the value of mtu.
The values in this case are just before the alloc_skb() are:

alloclen = 1480
alloc_extra = 136
datalen = 64095
fragheaderlen = 1480
fraglen = 65575
transhdrlen = 0
mtu = 1480

--
Thanks,
Tadeusz

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