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

[Dan Carpenter <dan@pereq.eu>]

On Thu, Nov 12, 2026 at 08:22:29AM +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.  When
> header.size is zero, kzalloc(0) returns ZERO_SIZE_PTR and the
> same read dereferences an invalid address.
> 
> Verify msg_size >= sizeof(header) in gb_connection_recv() so that
> the "Caller has made sure we at least have a message header"
> assumption in gb_operation_create_incoming() actually holds.
> 
> 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>
> ---
>  drivers/greybus/operation.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/greybus/operation.c b/drivers/greybus/operation.c
> index 7e12ffb2dd60..da53c0e026f0 100644
> --- a/drivers/greybus/operation.c
> +++ b/drivers/greybus/operation.c
> @@ -1047,6 +1047,13 @@ void gb_connection_recv(struct gb_connection *connection,
>  	/* Use memcpy as data may be unaligned */
>  	memcpy(&header, data, sizeof(header));
>  	msg_size = le16_to_cpu(header.size);
> +	if (msg_size < sizeof(header)) {
> +		dev_err_ratelimited(dev,
> +				    "%s: invalid message header size (%zu < %zu)\n",
> +				    connection->name, msg_size,
> +				    sizeof(header));
> +		return;
> +	}
>  	if (size < msg_size) {

Combine the conditions:

	if (msg_size < sizeof(header) || msg_size > size) {

regards,
dan carpenter

>  		dev_err_ratelimited(dev,
>  				    "%s: incomplete message 0x%04x of type 0x%02x received (%zu < %zu)\n",
> -- 
> 2.53.0
> 
> 
>