Re: [PATCH net] net: thunderbolt: Fix frags[] overflow by bounding frame_count

[Mika Westerberg]

On Wed, Jun 17, 2026 at 01:38:41AM +0800, Maoyi Xie wrote:
> tbnet_poll() assembles a multi-frame ThunderboltIP packet into one skb. The
> first frame goes into the skb linear area and every further frame is added as
> a page fragment.
> 
> 	skb_add_rx_frag(skb, skb_shinfo(skb)->nr_frags,
> 			page, hdr_size, frame_size,
> 			TBNET_RX_PAGE_SIZE - hdr_size);
> 
> A packet of frame_count frames therefore ends up with frame_count - 1
> fragments. tbnet_check_frame() only bounds the peer supplied frame_count to
> TBNET_RING_SIZE / 4 (64), which is far above MAX_SKB_FRAGS (17 by default). A
> peer that sends a packet of 19 or more small frames pushes nr_frags past
> MAX_SKB_FRAGS, so skb_add_rx_frag() writes past skb_shinfo()->frags[] and
> corrupts memory after the shared info.
> 
> Tighten the start of packet bound to MAX_SKB_FRAGS + 1 so a packet can never
> produce more fragments than frags[] can hold. This matches the recent skb
> frags overflow fixes in other receive paths, for example f0813bcd2d9d ("net:
> wwan: t7xx: fix potential skb->frags overflow in RX path") and 600dc40554dc
> ("net: usb: cdc-phonet: fix skb frags[] overflow in rx_complete()").
> 
> Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>
> ---
> Mika preferred the bound in tbnet_check_frame() over the nr_frags <
> MAX_SKB_FRAGS guard in tbnet_poll() that I first floated on the list, so this
> rejects the oversized packet up front. Reproduced under KASAN with a harness
> that mirrors the per-frame skb_add_rx_frag() loop.

Yeah the maximum size of "jumbo" packet over USB4NET is 64k == 16 frames,
so this should be fine. Thanks!

Acked-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>