Re: [PATCH v3] greybus: verify the received message size covers the message header

[Dan Carpenter <error27@gmail.com>]

On Fri, Nov 13, 2026 at 11:47:39PM +0000, Shunbo Shi wrote:
> In gb_connection_recv(), the size of the received data is checked
> against sizeof(struct gb_operation_msg_hdr) and against the message
> size encoded in the header (msg_size), but msg_size itself is never
> checked against the header size.
> 
> If a peer sends a message whose header claims a size smaller than
> the header itself (e.g. header.size == 3), the two existing checks
> both pass (size >= sizeof(header) and size >= msg_size), and the
> message is dispatched with the undersized msg_size.
> 
> In gb_operation_create_incoming(), this leads to an unsigned
> integer underflow in:
> 
> 	request_size = size - sizeof(struct gb_operation_msg_hdr);
> 
> The underflowed request_size then wraps back around in
> gb_operation_message_alloc():
> 
> 	message_size = payload_size + sizeof(*header);
> 
> causing kzalloc() to allocate a buffer that is too small to hold
> the message header.  When the response is later prepared in
> gb_operation_response_alloc(), reading
> request_header->operation_id reads past the end of the undersized
> allocation, triggering a KASAN slab-out-of-bounds report.
> 
> Link: https://lore.kernel.org/all/sashiko-outbox-210716@kernel.org/T/
> Fixes: d90c25b0a279 ("greybus: let operation layer examine incoming data")
> Reported-by: syzbot+0b456664585fa81a47f6@syzkaller.appspotmail.com
> Closes: https://syzbot.org/bug?extid=0b456664585fa81a47f6
> Signed-off-by: Shunbo Shi <shishunbo@cmss.chinamobile.com>
> ---
> Changes in v3:
> - combine the two separate conditions and unify the error message
>  as suggested by dan. Thanks!

Thanks!

Reviewed-by: Dan Carpenter <error27@gmail.com>

regards,
dan carpenter