Re: [PATCH net v3] net: wwan: iosm: bound device offsets in the MUX downlink decoder

[Simon Horman]

On Thu, Jun 25, 2026 at 02:17:28PM +0800, Maoyi Xie wrote:
> mux_dl_adb_decode() walks a chain of aggregated datagram tables using
> offsets and lengths taken from the modem. first_table_index,
> next_table_index, table_length, datagram_index and datagram_length are
> all device supplied le values. Only first_table_index was checked, and
> only for being non zero. The decoder then formed adth = block +
> adth_index and read the table header and the datagram entries with no
> bound against the received skb. A modem that reports an index or a
> length past the downlink buffer makes the decoder read out of bounds.
> 
> The buffer is IPC_MEM_MAX_DL_MUX_LITE_BUF_SIZE and skb->len is at most
> that, so skb->len is the real limit, but none of these in band offsets
> were checked against it.
> 
> The table chain is also followed with no forward progress check. The loop
> takes the next table from adth->next_table_index and stops only when that
> reaches zero. A modem can stage two tables that point at each other, so
> the loop never ends. It runs in softirq and clones the skb on every pass.
> 
> Validate every device offset and length against skb->len before use.
> The block header must fit. Each table header, on entry and after every
> next_table_index, must lie inside the skb. The datagram table must fit.
> Each datagram index and length must stay inside the skb. The header
> padding must not exceed the datagram length so the receive length does
> not wrap. Require each next_table_index to move forward so the chain
> cannot cycle.
> 
> This was reproduced under KASAN as a slab out of bounds read on a normal
> downlink receive once the iosm net device is up.
> 
> Fixes: 1f52d7b62285 ("net: wwan: iosm: Enable M.2 7360 WWAN card support")
> Suggested-by: Loic Poulain <loic.poulain@xxxxxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Maoyi Xie <maoyixie.tju@xxxxxxxxx>

Reviewed-by: Simon Horman <horms@xxxxxxxxxx>