On Sat, Apr 12, 2025 at 07:38:25PM +0100, Qasim Ijaz wrote:
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. We return 0 on control_read() failure here because returning a negative may trigger the "bmcr & BMCR_ANENABLE" check within mii_nway_restart.
Reported-by: syzbot syzbot+3361c2d6f78a3e0892f9@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3361c2d6f78a3e0892f9 Tested-by: syzbot syzbot+3361c2d6f78a3e0892f9@syzkaller.appspotmail.com Fixes: 4a476bd6d1d9 ("usbnet: New driver for QinHeng CH9200 devices") Cc: stable@vger.kernel.org Signed-off-by: Qasim Ijaz qasdev00@gmail.com
Reviewed-by: Andrew Lunn andrew@lunn.ch
Andrew