Change ownership I/O function handler

Prototype:

int (*chown)( resmgr_context_t *ctp,
              io_chown_t *msg,
              RESMGR_OCB_T *ocb ) 

Classification:

I/O function

Default handler:

iofunc_chown_default()

Helper functions:

iofunc_ability_check(), iofunc_chown()

Client functions:

chown(), fchown(), fchownat()

Messages:

_IO_CHOWN

Data structure:

struct _io_chown {
  uint16_t type;
  uint16_t combine_len;
  int32_t  gid;
  int32_t  uid;
};

typedef union {
  struct _io_chown i;
} io_chown_t;

Description:

Responsible for changing the user ID and group ID fields for the resource identified by the passed ocb to uid and gid, respectively. Note that the mount structure flag IOFUNC_PC_CHOWN_RESTRICTED and the OCB flag field should be examined to determine whether the filesystem allows chown() to be performed by non-root users.

Returns:

The status via the helper macro _RESMGR_STATUS().

Referenced by:

resmgr_io_funcs_t I/O table

Permission checking:

The default implementation iofunc_chown_default() calls the helper function iofunc_chown() to check the IOFUNC_PC_CHOWN_RESTRICTED flag to determine whether the user is allowed to change the user ID on the entry. The helper function also checks whether the client has the iofunc/chown (IOFUNC_ABILITY_CHOWN) dynamic ability (using iofunc_ability_check(), which allows it to set the user ID as if it were root. Finally, the helper checks to make sure it's not a read-only filesystem.

When iofunc_chown() sets the new user ID or group ID, it removes the set user ID and set group ID bits if they were set on the file. A value of -1 for the user or group ID means that the caller does not want to change that ID.