net: ch9200: fix uninitialised access during mii_nway_restart

Overview

In the Linux kernel, the following vulnerability has been resolved:

net: ch9200: fix uninitialised access during mii_nway_restart

In mii_nway_restart() the code attempts to call mii->mdio_read which is ch9200_mdio_read(). ch9200_mdio_read() utilises a local buffer called "buff", which is initialised with control_read(). 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.

Affected

• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 119766de4930ff40db9f36b960cb53b0c400e81b
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 33163c68d2e3061fa3935b5f0a1867958b1cdbd2
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 9da3e442714f7f4393ff01c265c4959c03e88c2f
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 9a350f30d65197354706b7759b5c89d6c267b1a9
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 6bd2569d0b2f918e9581f744df0263caf73ee76c
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 4da7fcc098218ff92b2e83a43f545c02f714cedd
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < cdaa6d1cb2ff1219c6c822b27655dd170ffb0f72
• Linux >= 4a476bd6d1d923922ec950ddc4c27b279f6901eb < 9ad0452c0277b816a435433cca601304cfac7c21
• Linux 4.3

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.