From: Daniel Yang <danielyangkang@xxxxxxxxx>
Date: Sat, 19 Oct 2024 00:11:39 -0700
> KMSAN detects uninitialized memory stored to memory by
> bpf_clone_redirect(). Adding a check to the transmission path to find
> malformed headers prevents this issue. Specifically, we check if the length
> of the data stored in skb is less than the minimum device header length.
> If so, drop the packet since the skb cannot contain a valid device header.
> Also check if mac_header_len(skb) is outside the range provided of valid
> device header lengths.
>
> Testing this patch with syzbot removes the bug.
>
> Fixes: 88264981f208 ("Merge tag 'sched_ext-for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext")
> Reported-by: syzbot+346474e3bf0b26bd3090@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://syzkaller.appspot.com/bug?extid=346474e3bf0b26bd3090
> Signed-off-by: Daniel Yang <danielyangkang@xxxxxxxxx>
> ---
> net/core/filter.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/net/core/filter.c b/net/core/filter.c
> index cd3524cb3..92d8f2098 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2191,6 +2191,13 @@ static int __bpf_redirect_common(struct sk_buff *skb, struct net_device *dev,
> return -ERANGE;
> }
>
> + if (unlikely(skb->len < dev->min_header_len ||
> + skb_mac_header_len(skb) < dev->min_header_len ||
> + skb_mac_header_len(skb) > dev->hard_header_len)) {
> + kfree_skb(skb);
> + return -ERANGE;
> + }
I believe this should go under IS_ENABLED(CONFIG_KMSAN) or
CONFIG_DEBUG_NET or so to not affect the regular configurations.
Or does this fix some real bug?
> +
> bpf_push_mac_rcsum(skb);
> return flags & BPF_F_INGRESS ?
> __bpf_rx_skb(dev, skb) : __bpf_tx_skb(dev, skb);
Thanks,
Olek
