Re: [PATCH net] net/packet: prevent TX_RING byte count overflow

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Ilkka Lappeteläinen wrote:
> tpacket_snd() drains every SEND_REQUEST frame in a TX ring and adds
> each valid packet length to the signed int len_sum. Userspace can
> recycle completed frames concurrently, so a single blocking send call
> is not bounded by the ring size.
> 
> After enough successful transmissions len_sum wraps into the negative
> range. In particular, 65536 65535-byte frames followed by a 65007-byte
> frame produce 0xfffffdef, or -EIOCBQUEUED. sock_sendmsg_nosec() treats
> that as an impossible return and triggers a BUG. On systems configured
> to panic on oops, a CAP_NET_RAW holder can panic the host kernel.
> 
> Stop before the next frame would make the byte count exceed INT_MAX.
> The positive short count leaves that frame pending for a later send
> call.
> 
> A two-thread TPACKET_V2 reproducer triggered the BUG on an arm64 build
> of Linux 7.3-rc4. With this change, the same reproducer returned the
> expected positive short count without an oops.
> 
> Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Ilkka Lappeteläinen <ilkka.lappetelainen@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>