genfs_can_access(9) - NetBSD Manual Pages

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GENFS_CAN_ACCESS(9)    NetBSD Kernel Developer's Manual    GENFS_CAN_ACCESS(9)


NAME

     genfs_can_access -- generate an access control decision using vnode
     parameters


SYNOPSIS

     #include <miscfs/genfs/genfs.h>

     int
     genfs_can_access(vnode_t *vp, kauth_cred_t cred, uid_t file_uid,
         gid_t file_gid, mode_t file_mode, struct acl *acl,
         accmode_t accmode);


DESCRIPTION

     This call implements the logic for the UNIX discretionary file security
     model common to many file systems in FreeBSD.  It accepts the vnode vp,
     requesting credential cred, permissions via owning UID file_uid, owning
     GID file_gid, file permissions file_mode, access ACL for the file acl,
     desired access mode accmode,

     This call is intended to support implementations of VOP_ACCESS(9), which
     will use their own access methods to retrieve the vnode properties, and
     then invoke vaccess() in order to perform the actual check.  Implementa-
     tions of VOP_ACCESS(9) may choose to implement additional security mecha-
     nisms whose results will be composed with the return value.

     The algorithm used by genfs_can_access() selects a component of the file
     permission bits based on comparing the passed credential, file owner, and
     file group.  If the credential's effective UID matches the file owner,
     then the owner component of the permission bits is selected.  If the UID
     does not match, then the credential's effective GID, followed by addi-
     tional groups, are compared with the file group--if there is a match,
     then the group component of the permission bits is selected.  If neither
     the credential UID or GIDs match the passed file owner and group, then
     the other component of the permission bits is selected.

     Once appropriate protections are selected for the current credential, the
     requested access mode, in combination with the vnode type, will be com-
     pared with the discretionary rights available for the credential.  If the
     rights granted by discretionary protections are insufficient, then super-
     user privilege, if available for the credential, will also be considered.


RETURN VALUES

     genfs_can_access() will return 0 on success, or a non-zero error value on
     failure.


ERRORS

     [EACCES]           Permission denied.  An attempt was made to access a
                        file in a way forbidden by its file access permis-
                        sions.

     [EPERM]            Operation not permitted.  An attempt was made to per-
                        form an operation limited to processes with appropri-
                        ate privileges or to the owner of a file or other
                        resource.


SEE ALSO

     genfs(9), genfs_can_access_acl_nfs4(9), genfs_can_access_acl_posix1e(9),
     vnode(9), VOP_ACCESS(9)


AUTHORS

     This manual page and the current implementation of vaccess() were written
     by Robert Watson.

NetBSD 10.1                    January 17, 2022                    NetBSD 10.1