net/packet: prevent TX_RING byte count overflow

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
Signed-off-by: Ilkka Lappeteläinen <ilkka.lappetelainen@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260925124829.6595-1-ilkka.lappetelainen@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

0 files changed, 0 insertions, 0 deletions