Change the permissions mask on a key
#include <keyutils.h> long keyctl_setperm(key_serial_t key, key_perm_t perm);
keyctl_setperm() changes the permissions mask on a key.
A process that does not have the SysAdmin capability may not change the permissions mask on a key that doesn't have the same UID as the caller.
The caller must have setattr permission on a key to be able change its permissions mask.
The permissions mask is a bitwise-OR of the following flags:
KEY_xxx_VIEW
Grant permission to view the attributes of a key.
KEY_xxx_READ
Grant permission to read the payload of a key or to list a keyring.
KEY_xxx_WRITE
Grant permission to modify the payload of a key or to add or remove links to/from a keyring.
KEY_xxx_SEARCH
Grant permission to find a key or to search a keyring.
KEY_xxx_LINK
Grant permission to make links to a key.
KEY_xxx_SETATTR
Grant permission to change the ownership and permissions attributes of a key.
KEY_xxx_ALL
Grant all the above.
The 'xxx' in the above should be replaced by one of:
POS
Grant the permission to a process that possesses the key (has it attached searchably to one of the process's keyrings).
USR
Grant the permission to a process with the same UID as the key.
GRP
Grant the permission to a process with the same GID as the key, or with a match for the key's GID amongst that process's Groups list.
OTH
Grant the permission to any other process.
Examples include: KEY_POS_VIEW, KEY_USR_READ, KEY_GRP_SEARCH and KEY_OTH_ALL.
User, group and other grants are exclusive: if a process qualifies in the 'user' category, it will not qualify in the 'groups' category; and if a process qualifies in either 'user' or 'groups' then it will not qualify in the 'other' category.
Possessor grants are cumulative with the grants from the 'user', 'groups' and 'other' categories.
On success keyctl_setperm() returns 0 . On error, the value -1 will be returned and errno will have been set to an appropriate error.
ENOKEY
The specified key does not exist.
EKEYEXPIRED
The specified key has expired.
EKEYREVOKED
The specified key has been revoked.
EACCES
The named key exists, but does not grant setattr permission to the calling process.
This is a library function that can be found in libkeyutils. When linking, -lkeyutils should be specified to the linker.