s390/zcrypt: Fix buffer over-read in cca_cipher2protkey

Overview

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

s390/zcrypt: Fix buffer over-read in cca_cipher2protkey

Add validation of both the actual key buffer size and token length fields in all the cca_check_sec*token() functions. Additionally check in cca_gencipherkey() for possible underflow with returned key size.

The CCA token structures contain user-controlled len fields that were used in operations without proper validation against both the actual buffer size and minimum token structure size. An attacker could set this field larger than the actual buffer size, leading to reading beyond buffer boundaries. This may result in a kernel crash or exposure of memory via sending this as part of a request down to the crypto card. Also an attacker could have used a very small len value and thus enforce a buffer under-run which may produce similar effects as a over-read.

So now a key must

• key buf length must be at least sizeof the token struct
• the key len field inside the token must fit into the range of sizeof key token struct ... key buf length

Affected

• Linux >= 4bc123b18ce6ae6c42c69d0456b5acbd2f7bc8bd < a57fd7fcdb63e2d5ceac78bbe825ec986062a9da
• Linux >= 4bc123b18ce6ae6c42c69d0456b5acbd2f7bc8bd < 3b2abee2a678607ae27975bc6833785c2002df43
• Linux >= 4bc123b18ce6ae6c42c69d0456b5acbd2f7bc8bd < 36b230835b8a008266aad22168ca52afacc8a58d
• Linux 5.4

Remediation

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