getpeereid(3) [osx man page]
GETPEEREID(3) BSD Library Functions Manual GETPEEREID(3) NAME
getpeereid -- get the effective credentials of a UNIX-domain peer LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <sys/types.h> #include <unistd.h> int getpeereid(int s, uid_t *euid, gid_t *egid); DESCRIPTION
The getpeereid() function returns the effective user and group IDs of the peer connected to a UNIX-domain socket. The argument s must be a UNIX-domain socket (unix(4)) of type SOCK_STREAM on which either connect(2) or listen(2) have been called. The effective used ID is placed in euid, and the effective group ID in egid. The credentials returned to the listen(2) caller are those of its peer at the time it called connect(2); the credentials returned to the connect(2) caller are those of its peer at the time it called listen(2). This mechanism is reliable; there is no way for either side to influence the credentials returned to its peer except by calling the appropriate system call (i.e., either connect(2) or listen(2)) under different effective credentials. One common use of this routine is for a UNIX-domain server to verify the credentials of its client. Likewise, the client can verify the cre- dentials of the server. IMPLEMENTATION NOTES
On FreeBSD, getpeereid() is implemented in terms of the LOCAL_PEERCRED unix(4) socket option. RETURN VALUES
The getpeereid() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indi- cate the error. ERRORS
The getpeereid() function fails if: [EBADF] The argument s is not a valid descriptor. [ENOTSOCK] The argument s is a file, not a socket. [ENOTCONN] The argument s does not refer to a socket on which connect(2) or listen(2) have been called. [EINVAL] The argument s does not refer to a socket of type SOCK_STREAM, or the kernel returned invalid data. SEE ALSO
connect(2), getpeername(2), getsockname(2), getsockopt(2), listen(2), unix(4) HISTORY
The getpeereid() function appeared in FreeBSD 4.6. BSD
July 15, 2001 BSD
Check Out this Related Man Page
UNIX(4) BSD Kernel Interfaces Manual UNIX(4) NAME
unix -- UNIX-domain protocol family SYNOPSIS
#include <sys/types.h> #include <sys/un.h> DESCRIPTION
The UNIX-domain protocol family is a collection of protocols that provides local (on-machine) interprocess communication through the normal socket(2) mechanisms. The UNIX-domain family supports the SOCK_STREAM and SOCK_DGRAM socket types and uses file system pathnames for addressing. ADDRESSING
UNIX-domain addresses are variable-length file system pathnames of at most 104 characters. The include file <sys/un.h> defines this address: struct sockaddr_un { u_char sun_len; u_char sun_family; char sun_path[104]; }; Binding a name to a UNIX-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-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-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-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. PROTOCOLS
The UNIX-domain protocol family is comprised of simple transport protocols that support the SOCK_STREAM and SOCK_DGRAM abstractions. SOCK_STREAM sockets also support the communication of UNIX file descriptors through the use of the msg_control field in the msg argument to sendmsg(2) and recvmsg(2). Any valid descriptor may be sent in a message. The file descriptor(s) to be passed are described using a struct cmsghdr that is defined in the include file <sys/socket.h>. The type of the message is SCM_RIGHTS, and the data portion of the messages is an array of integers repre- senting 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 with a call to dup(2). Per-process descriptor flags, set with fcntl(2), are not passed to a receiver. Descriptors that are awaiting delivery, or that are purposely not received, are automatically closed by the system when the destination socket is closed. The effective credentials (i.e., the user ID and group list) of a peer on a SOCK_STREAM socket may be obtained using the LOCAL_PEERCRED socket option. This may be used by a server to obtain and verify the credentials of its client, and vice versa by the client to verify the credentials of the server. These will arrive in the form of a filled in struct xucred (defined in <sys/ucred.h>). 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 influ- ence the credentials presented to its peer except by calling the appropriate system call (e.g., connect(2) or listen(2)) under different effective credentials. UNIX domain sockets support a number of socket options which can be set with setsockopt(2) and tested with getsockopt(2): LOCAL_CREDS This option may be enabled on a SOCK_DGRAM or a SOCK_STREAM socket. This option provides a mechanism for the receiver to receive the credentials of the process 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 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 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. SEE ALSO
socket(2), intro(4) "An Introductory 4.3 BSD Interprocess Communication Tutorial", PS1, 7. "An Advanced 4.3 BSD Interprocess Communication Tutorial", PS1, 8. BSD July 15, 2001 BSD