Re: [PATCH net v2] net: skbuff: make skb_copy_and_csum_bits() report unreadable frags

[Josef Bacik]

On Tue, Oct 13, 2026 at 06:05:30PM +0000, netdev-bot+sinfo@xxxxxxxxxx wrote:
>  - Whether the issue was actually triggered, or is only theoretical
>    (e.g. found by code inspection). If it was triggered please include
>    the symptoms, like the stack trace or error messages.

It was found by the Sashiko review of ab9414ed70bd and then triggered
with a test module, not on devmem hardware.  The module builds a TCPv4
GSO skb with 3000 bytes of payload in a page frag marked unreadable and
calls skb_segment() on it with features == 0.  Without this patch that
returns 3 segments whose payloads are all zeroes, each with a
SKB_GSO_CB()->csum of 0, which is the correct checksum for zeroes.
There's no stack trace or error, the data is just silently replaced.
With this patch skb_segment() returns -EFAULT.

Thanks,
Josef