Re: [PATCH net v2] net: usb: catc: bound the RX packet length in catc_rx_done()

[Simon Horman]

On Tue, Sep 15, 2026 at 12:06:58AM +0100, Aamir Ahmed wrote:
> catc_rx_done() walks a multi-packet URB, reading a two-byte length from
> each packet header. Its bound, pkt_len > urb->actual_length, ignores the
> header offset and compares against the whole transfer rather than the
> bytes left from pkt_start, so a crafted packet header makes
> skb_copy_to_linear_data() read past the buffer.
> 
> A length below ETH_HLEN is also accepted, including zero, and
> eth_type_trans() then reads a MAC header from the uninitialised tailroom
> of a shorter skb. The is_f5u011 branch takes its length straight from
> the transfer, so a zero-length URB reaches the same path.
> 
> Track the bytes remaining from the current packet, and reject a header
> that does not fit, a length past what is left, and a length below an
> Ethernet header.
> 
> A transfer shorter than an Ethernet header, including a zero-length one,
> previously became a runt skb passed to netif_rx() and counted as
> received; it is now counted in rx_length_errors and ends the walk.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Assisted-by: LLM
> Signed-off-by: Aamir Ahmed <elb12345@xxxxxxxxxxxxx>
> ---
> v2:
>   - reject pkt_len below ETH_HLEN, covering the is_f5u011 branch too (Sashiko)
>   - hoist the remaining-bytes calculation so one check bounds both ends
>   - drop Cc: stable; no conforming device reaches this
>   - add Assisted-by: LLM
> v1: https://lore.kernel.org/netdev/AS8P251MB00013A0DCA600A79DC58B0FEC8B22@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> 
> Sashiko also suggested a sanity maximum on pkt_len. I left it out: PKT_SZ
> would reject the 1537-1600 byte transfers the is_f5u011 path allows, since
> RX_PKT_SZ is 1600, and dev->mtu excludes the MAC header that pkt_len
> includes.
> 
> Built with W=1 (catc.o) on x86_64; no warnings. I have no CATC hardware,
> so this is not runtime-tested.

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>