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#include <sys/types.h>
#include <sys/un.h>
struct sockaddr_un {
u_char sun_len;
u_char sun_family;
char sun_path[104];
};
Binding a name to a Unix Ns -domain socket with bind(2) causes a socket file to be created in the file system. This file is not removed when the socket is closed — unlink(2) must be used to remove the file.
The length of Unix Ns -domain address, required by bind(2) and connect(2), can be calculated by the macro SUN_LEN() defined in <sys/un.h>. The sun_path field must be terminated by a NUL character to be used with SUN_LEN(), but the terminating NUL is not part of the address.
The Unix Ns -domain protocol family does not support broadcast addressing or any form of "wildcard" matching on incoming messages. All addresses are absolute- or relative-pathnames of other Unix Ns -domain sockets. Normal file system access-control mechanisms are also applied when referencing pathnames; e.g., the destination of a connect(2) or sendto(2) must be writable.
To send file descriptors, the type of the message is SCM_RIGHTS, and the data portion of the messages is an array of integers representing the file descriptors to be passed. The number of descriptors being passed is defined by the length field of the message; the length field is the sum of the size of the header plus the size of the array of file descriptors.
The received descriptor is a duplicate of the sender's descriptor, as if it were created via dup(fd) or fcntl(fd, F_DUPFD_CLOEXEC, 0) depending on whether MSG_CMSG_CLOEXEC is passed in the recvmsg(2) call. Descriptors that are awaiting delivery, or that are purposely not received, are automatically closed by the system when the destination socket is closed.
Credentials of the sending process can be transmitted explicitly using a control message of type SCM_CREDS with a data portion of type struct cmsgcred, defined in <sys/socket.h> as follows:
struct cmsgcred {
pid_t cmcred_pid; /* PID of sending process */
uid_t cmcred_uid; /* real UID of sending process */
uid_t cmcred_euid; /* effective UID of sending process */
gid_t cmcred_gid; /* real GID of sending process */
short cmcred_ngroups; /* number of groups */
gid_t cmcred_groups[CMGROUP_MAX]; /* groups */
};
The sender should pass a zeroed buffer which will be filled in by the system.
The group list is truncated to at most CMGROUP_MAX GIDs.
The process ID cmcred_pid should not be looked up (such as via the KERN_PROC_PID sysctl) for making security decisions. The sending process could have exited and its process ID already been reused for a new process.
| LOCAL_CREDS |
This option may be enabled on
SOCK_DGRAM,
SOCK_SEQPACKET,
or a
SOCK_STREAM
socket.
This option provides a mechanism for the receiver to
receive the credentials of the process calling
write(2),
send(2),
sendto(2)
or
sendmsg(2)
as a
recvmsg(2)
control message.
The
msg_control
field in the
msghdr
structure points to a buffer that contains a
cmsghdr
structure followed by a variable length
sockcred
structure, defined in
<sys/socket.h>
as follows:
struct sockcred {
uid_t sc_uid; /* real user id */
uid_t sc_euid; /* effective user id */
gid_t sc_gid; /* real group id */
gid_t sc_egid; /* effective group id */
int sc_ngroups; /* number of supplemental groups */
gid_t sc_groups[1]; /* variable length */
};
The current implementation truncates the group list to at most CMGROUP_MAX groups. The SOCKCREDSIZE() macro computes the size of the sockcred structure for a specified number of groups. The cmsghdr fields have the following values: cmsg_len = CMSG_LEN(SOCKCREDSIZE(ngroups)) cmsg_level = SOL_SOCKET cmsg_type = SCM_CREDS On SOCK_STREAM and SOCK_SEQPACKET sockets credentials are passed only on the first read from a socket, then the system clears the option on the socket. This option and the above explicit struct cmsgcred both use the same value SCM_CREDS but incompatible control messages. If this option is enabled and the sender attached a SCM_CREDS control message with a struct cmsgcred, it will be discarded and a struct sockcred will be included. Many setuid programs will write(2) data at least partially controlled by the invoker, such as error messages. Therefore, a message accompanied by a particular sc_euid value should not be trusted as being from that user. |
| LOCAL_CONNWAIT | |
| Used with SOCK_STREAM sockets, this option causes the connect(2) function to block until accept(2) has been called on the listening socket. | |
| LOCAL_PEERCRED | |
Requested via
getsockopt(2)
on a
SOCK_STREAM
or
SOCK_SEQPACKET
socket returns credentials of the remote side.
These will arrive in the form of a filled in
xucred
structure, defined in
<sys/ucred.h>
as follows:
struct xucred {
u_int cr_version; /* structure layout version */
uid_t cr_uid; /* effective user id */
short cr_ngroups; /* number of groups */
gid_t cr_groups[XU_NGROUPS]; /* groups */
pid_t cr_pid; /* process id of the sending process */
};
The
cr_version
fields should be checked against
XUCRED_VERSION
define.
The credentials presented to the server (the listen(2) caller) are those of the client when it called connect(2); the credentials presented to the client (the connect(2) caller) are those of the server when it called listen(2). This mechanism is reliable; there is no way for either party to influence the credentials presented to its peer except by calling the appropriate system call (e.g., connect(2) or listen(2)) under different effective credentials. To reliably obtain peer credentials on a SOCK_DGRAM socket refer to the LOCAL_CREDS socket option. | |
PS1, 7, An Introductory 4.3 BSD Interprocess Communication Tutorial,
PS1, 8, An Advanced 4.3 BSD Interprocess Communication Tutorial,
| UNIX (4) | August 7, 2021 |
| Main index | Section 4 | 日本語 | Options |
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