On Tue, Feb 18, 2025 at 02:10:08AM +0100, Andrew Lunn wrote:

On Tue, Feb 18, 2025 at 12:24:43AM +0000, Qasim Ijaz wrote:

quoted

In mii_nway_restart() during the line:

	bmcr = mii->mdio_read(mii->dev, mii->phy_id, MII_BMCR);

The code attempts to call mii->mdio_read which is ch9200_mdio_read().

ch9200_mdio_read() utilises a local buffer, which is initialised 
with control_read():

	unsigned char buff[2];
	
However buff is conditionally initialised inside control_read():

	if (err == size) {
		memcpy(data, buf, size);
	}

If the condition of "err == size" is not met, then buff remains 
uninitialised. Once this happens the uninitialised buff is accessed 
and returned during ch9200_mdio_read():

	return (buff[0] | buff[1] << 8);
	
The problem stems from the fact that ch9200_mdio_read() ignores the
return value of control_read(), leading to uinit-access of buff.

To fix this we should check the return value of control_read()
and return early on error.

What about get_mac_address()?

If you find a bug, it is a good idea to look around and see if there
are any more instances of the same bug. I could be wrong, but it seems
like get_mac_address() suffers from the same problem?

Thank you for the feedback Andrew. I checked get_mac_address() before
sending this patch and to me it looks like it does check the return value of
control_read(). It accumulates the return value of each control_read() call into 
rd_mac_len and then checks if it not equal to what is expected (ETH_ALEN which is 6),
I believe each call should return 2.

	Andrew