Commits on Aug 19, 2022

1. Limit KeyctlString() to DESCRIBE / GET_SECURITY …

   KeyctlString() treats the query data buffer filled by the keyctl(2) syscall as C-Style string with a trailing NULL byte.
   
   This is only true for two cmds - KEYCTL_DESCRIBE and KEYCTL_GET_SECURITY.
   
   Both are guaranteed to return at least an empty (C) string (i.e. a one-byte-sized buffer containing only a NULL byte) if the requested attribute is not set at all.
   
   Other cmds that can be passed to the system call - KEYCTL_READ most prominently - return explicitly-sized binary data; NULL bytes have no special meaning for these queries and are _part_ of the returned data, irrespective of where in the buffer they occur. Returning nothing (zero-length) can also be permitted; example of this is a KEYCTL_READ on an empty keyring.
   
   If KeyctlString() is called with any of the keyctl(2) query commands other than the two that are guaranteed to return C-style strings, it will either:
   * panic (attempting to strip trailing null bytes from zero-sized buffers), or
   * truncate the returned data in error (for KEYCTL_READ of a key payload).
   
   Therefore, restrict the use.

   

   fhofmannCF authored Aug 19, 2022
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