Hello Michal,
2015-12-28, 15:01:57 +0100, Michal Kubecek wrote:
> Recent fix "net: add length argument to
> skb_copy_and_csum_datagram_iovec" added to some pre-3.19 stable
> branches, namely
>
> stable-3.2.y: commit 127500d724f8
> stable-3.12.y: commit 3e1ac3aafbd0
>
> doesn't handle truncated reads correctly. If read length is shorter than
> incoming datagram (but non-zero) and first segment of target iovec is
> sufficient for read length, skb_copy_and_csum_datagram() is used to copy
> checksum the data while copying it. For truncated reads this means only
> the copied part is checksummed (rather than the whole datagram) so that
> the check almost always fails.
I just ran into this issue too, sorry I didn't notice it earlier :(
> Add checksum of the remaining part so that the proper checksum of the
> whole datagram is computed and checked. Special care must be taken if
> the copied length is odd.
>
> For zero read length, we don't have to copy anything but we still should
> check the checksum so that a peek doesn't return with a datagram which
> is invalid and wouldn't be returned by an actual read.
>
> Signed-off-by: Michal Kubecek <mkubecek@xxxxxxx>
> ---
> net/core/datagram.c | 26 +++++++++++++++++++++-----
> 1 file changed, 21 insertions(+), 5 deletions(-)
>
> diff --git a/net/core/datagram.c b/net/core/datagram.c
> index f22f120771ef..af4bf368257c 100644
> --- a/net/core/datagram.c
> +++ b/net/core/datagram.c
> @@ -809,13 +809,14 @@ int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
> int hlen, struct iovec *iov, int len)
> {
> __wsum csum;
> - int chunk = skb->len - hlen;
> + int full_chunk = skb->len - hlen;
> + int chunk = min_t(int, full_chunk, len);
>
> - if (chunk > len)
> - chunk = len;
> -
> - if (!chunk)
> + if (!chunk) {
> + if (__skb_checksum_complete(skb))
> + goto csum_error;
> return 0;
> + }
>
> /* Skip filled elements.
> * Pretty silly, look at memcpy_toiovec, though 8)
> @@ -833,6 +834,21 @@ int skb_copy_and_csum_datagram_iovec(struct sk_buff *skb,
> if (skb_copy_and_csum_datagram(skb, hlen, iov->iov_base,
> chunk, &csum))
> goto fault;
> + if (full_chunk > chunk) {
> + if (chunk % 2) {
> + __be16 odd = 0;
> +
> + if (skb_copy_bits(skb, hlen + chunk,
> + (char *)&odd + 1, 1))
> + goto fault;
> + csum = add32_with_carry(odd, csum);
> + csum = skb_checksum(skb, hlen + chunk + 1,
> + full_chunk - chunk - 1,
> + csum);
> + } else
> + csum = skb_checksum(skb, hlen + chunk,
> + full_chunk - chunk, csum);
> + }
> if (csum_fold(csum))
> goto csum_error;
> if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
> --
> 2.6.4
This adds quite a bit of complexity. I am considering a revert of my
buggy patch, and use what Eric Dumazet suggested instead:
https://patchwork.ozlabs.org/patch/543562/
What do you think?
Eric, would you submit your patch formally?
Thanks
--
Sabrina
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