Re: Patch: use SCM_CREDS authentication over PF_LOCAL sockets - Mailing list pgsql-patches

From Bruce Momjian
Subject Re: Patch: use SCM_CREDS authentication over PF_LOCAL sockets
Date
Msg-id 200108170335.f7H3Zev10533@candle.pha.pa.us
Whole thread Raw
In response to Patch: use SCM_CREDS authentication over PF_LOCAL sockets  (wollman@LCS.MIT.EDU)
List pgsql-patches
> <<On Thu, 16 Aug 2001 00:34:14 -0400 (EDT), Bruce Momjian <pgman@candle.pha.pa.us> said:
>
> > OK, here is a cleaned up version of the patch that will apply to current
> > CVS.  I worked it into the SO_PEERCRED code.  I made some changes so it
> > compiles on BSD/OS.  I am getting "Invalid Argument" from libpq's
> > sending of the credentials on BSD/OS.
>
> There are some funky alignment macros that you probably need to use on
> BSD/OS.  Also, as written this will break on NetBSD and OpenBSD for
> reasons I have already noted (the structure is named something
> different there), and those systems will also require the alignment
> macros.  (Basically, putting the two structures in another larger
> structure is a shortcut in my implementation which only works because
> the compiler puts the right amount of padding in; on those other
> systems, more padding is required.)

OK, attached is my current version of the patch.  Would you download the
snapshot or CVS and let me know if this works on FreeBSD.  Even if you
can't run it, can you tell me if it compiles.

Also, attached is the BSD/OS manual page that shows the use of the
macros for retrieving SCM.  Can you add that and send me an updated
patch?  Also, can you check to see if FreeBSD requires you to send the
full struct with empty cred, or if you can just send the header without
the struct.  You will see in my patch for the libpq client part that
BSD/OS doesn't want the extra struct.

Looks like 7.2 is going to have overhauled authentication, and I would
really like to get this SCM stuff nailed down on as many platforms as
possible before going beta, which may happen as early as September 1.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026
Index: src/backend/libpq/auth.c
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/backend/libpq/auth.c,v
retrieving revision 1.58
diff -c -r1.58 auth.c
*** src/backend/libpq/auth.c    2001/08/16 04:27:18    1.58
--- src/backend/libpq/auth.c    2001/08/16 14:56:42
***************
*** 15,24 ****

  #include "postgres.h"

! #include <sys/types.h>            /* needed by in.h on Ultrix */
  #include <netinet/in.h>
  #include <arpa/inet.h>
-
  #include "libpq/auth.h"
  #include "libpq/crypt.h"
  #include "libpq/hba.h"
--- 15,29 ----

  #include "postgres.h"

! #include <sys/types.h>
! #include <sys/socket.h>            /* for SCM_CREDS */
! #ifdef SCM_CREDS
! #include <sys/uio.h>            /* for struct iovec */
! #include <sys/ucred.h>
! #include <errno.h>
! #endif
  #include <netinet/in.h>
  #include <arpa/inet.h>
  #include "libpq/auth.h"
  #include "libpq/crypt.h"
  #include "libpq/hba.h"
***************
*** 28,39 ****
  #include "miscadmin.h"

  static void sendAuthRequest(Port *port, AuthRequest areq);
-
  static int    checkPassword(Port *port, char *user, char *password);
  static int    old_be_recvauth(Port *port);
  static int    map_old_to_new(Port *port, UserAuth old, int status);
  static void auth_failed(Port *port);
-
  static int    recv_and_check_password_packet(Port *port);
  static int    recv_and_check_passwordv0(Port *port);

--- 33,42 ----
***************
*** 493,498 ****
--- 496,507 ----
              break;

          case uaIdent:
+ #ifdef SCM_CREDS
+             /* If we are doing ident on unix-domain sockets,
+                we are going to use SCM_CREDS, if defined. */
+             if (port->raddr.sa.sa_family ==    AF_UNIX)
+                 sendAuthRequest(port, AUTH_REQ_SCM_CREDS);
+ #endif
              status = authident(port);
              break;

Index: src/backend/libpq/hba.c
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/backend/libpq/hba.c,v
retrieving revision 1.63
diff -c -r1.63 hba.c
*** src/backend/libpq/hba.c    2001/08/16 04:27:18    1.63
--- src/backend/libpq/hba.c    2001/08/16 14:56:42
***************
*** 19,24 ****
--- 19,30 ----
  #include <errno.h>
  #include <pwd.h>
  #include <sys/types.h>
+ #include <sys/socket.h>            /* for SCM_CREDS */
+ #ifdef SCM_CREDS
+ #include <sys/uio.h>            /* for struct iovec */
+ #include <sys/ucred.h>
+ #include <errno.h>
+ #endif
  #include <fcntl.h>
  #include <sys/socket.h>
  #include <netinet/in.h>
***************
*** 863,869 ****
  static bool
  ident_unix(int sock, char *ident_user)
  {
! #ifdef SO_PEERCRED
      /* Linux style: use getsockopt(SO_PEERCRED) */
      struct ucred    peercred;
      ACCEPT_TYPE_ARG3 so_len = sizeof(peercred);
--- 869,959 ----
  static bool
  ident_unix(int sock, char *ident_user)
  {
! #ifdef SCM_CREDS
!     struct msghdr msg;
!     struct {
!         struct cmsghdr hdr;
! #ifndef fc_uid
!         struct cmsgcred cred;
! #define cruid cmcred_uid
! #else
!         struct fcred cred;
! #define cruid fc_uid
! #endif
!     } cmsg;
!     struct iovec iov;
!     char buf;
!     char namebuf[SM_USER + 1];
!     struct passwd *pw;
!
!     msg.msg_name = NULL;
!     msg.msg_namelen = 0;
!     msg.msg_iov = &iov;
!     msg.msg_iovlen = 1;
!     msg.msg_control = (char *)&cmsg;
!     msg.msg_controllen = sizeof cmsg;
!     msg.msg_flags = 0;
!
!     /*
!      * The one character which is received here is not meaningful;
!      * its purposes is only to make sure that recvmsg() blocks
!      * long enough for the other side to send its credentials.
!      */
!     iov.iov_base = &buf;
!     iov.iov_len = 1;
!
!     if (recvmsg(sock, &msg, 0) < 0) {
!         snprintf(PQerrormsg, PQERRORMSG_LENGTH,
!              "ident_unix: error receiving credentials: %s\n",
!              strerror(errno));
! errout:
!         fputs(PQerrormsg, stderr);
!         pqdebug("%s", PQerrormsg);
!
!         return false;
!     }
!
!     /*
!      * Make sure we got the right kind of message.
!      */
!     if (cmsg.hdr.cmsg_len != sizeof cmsg
!         || cmsg.hdr.cmsg_level != SOL_SOCKET
!         || cmsg.hdr.cmsg_type != SCM_CREDS) {
!         snprintf(PQerrormsg, PQERRORMSG_LENGTH,
!              "ident_unix: protocol error receiving credentials\n");
!         goto errout;
!     }
!
!     snprintf(PQerrormsg, PQERRORMSG_LENGTH,
!          "ident_unix: pid %lu, uid %lu\n",
! #ifndef fc_uid
!          (unsigned long)cmsg.cred.cmcred_pid,
! #else
!          (unsigned long)0, /* unavailable */
! #endif
!          (unsigned long)cmsg.cred.cruid);
!     pqdebug("%s", PQerrormsg);
!
!     strncpy(namebuf, ident_user, SM_USER);
!     namebuf[SM_USER] = '\0';
!
!     pw = getpwnam(namebuf);
!     if (pw == NULL) {
!         snprintf(PQerrormsg, PQERRORMSG_LENGTH,
!              "ident_unix: unknown local user %s\n",
!              namebuf);
!         goto errout;
!     }
!
!     if (pw->pw_uid != cmsg.cred.cruid) {
!         snprintf(PQerrormsg, PQERRORMSG_LENGTH,
!              "ident_unix: %s's uid %lu != real uid %lu\n",
!              namebuf, (unsigned long)pw->pw_uid,
!              (unsigned long)cmsg.cred.cruid);
!         goto errout;
!     }
!     return true;
! #elif SO_PEERCRED
      /* Linux style: use getsockopt(SO_PEERCRED) */
      struct ucred    peercred;
      ACCEPT_TYPE_ARG3 so_len = sizeof(peercred);
***************
*** 899,905 ****

      return true;

! #else /* not SO_PEERCRED */

      snprintf(PQerrormsg, PQERRORMSG_LENGTH,
               "IDENT auth is not supported on local connections on this platform\n");
--- 989,995 ----

      return true;

! #else

      snprintf(PQerrormsg, PQERRORMSG_LENGTH,
               "IDENT auth is not supported on local connections on this platform\n");
***************
*** 907,913 ****
      pqdebug("%s", PQerrormsg);
      return false;

! #endif /* SO_PEERCRED */
  }

  /*
--- 997,1003 ----
      pqdebug("%s", PQerrormsg);
      return false;

! #endif
  }

  /*
Index: src/backend/libpq/pg_hba.conf.sample
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/backend/libpq/pg_hba.conf.sample,v
retrieving revision 1.24
diff -c -r1.24 pg_hba.conf.sample
*** src/backend/libpq/pg_hba.conf.sample    2001/08/15 18:42:15    1.24
--- src/backend/libpq/pg_hba.conf.sample    2001/08/16 14:56:47
***************
*** 125,136 ****
  #   ident:    For TCP/IP connections, authentication is done by contacting
  #        the ident server on the client host.  (CAUTION: this is only
  #        as secure as the client machine!)  On machines that support
! #        SO_PEERCRED socket requests, this method also works for
! #        local Unix-domain connections.  AUTH_ARGUMENT is required:
! #        it determines how to map remote user names to Postgres user
! #        names.  The AUTH_ARGUMENT is a map name found in the
! #        $PGDATA/pg_ident.conf file. The connection is accepted if
! #        that file contains an entry for this map name with the
  #        ident-supplied username and the requested Postgres username.
  #        The special map name "sameuser" indicates an implied map
  #        (not in pg_ident.conf) that maps each ident username to the
--- 125,136 ----
  #   ident:    For TCP/IP connections, authentication is done by contacting
  #        the ident server on the client host.  (CAUTION: this is only
  #        as secure as the client machine!)  On machines that support
! #        SO_PEERCRED or SCM_CREDS socket requests, this method also
! #        works for local Unix-domain connections.  AUTH_ARGUMENT is
! #        required: it determines how to map remote user names to
! #        Postgres user names.  The AUTH_ARGUMENT is a map name found
! #        in the $PGDATA/pg_ident.conf file. The connection is accepted
! #        if that file contains an entry for this map name with the
  #        ident-supplied username and the requested Postgres username.
  #        The special map name "sameuser" indicates an implied map
  #        (not in pg_ident.conf) that maps each ident username to the
Index: src/include/libpq/pqcomm.h
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/include/libpq/pqcomm.h,v
retrieving revision 1.57
diff -c -r1.57 pqcomm.h
*** src/include/libpq/pqcomm.h    2001/08/16 04:27:18    1.57
--- src/include/libpq/pqcomm.h    2001/08/16 14:56:48
***************
*** 133,138 ****
--- 133,139 ----
  #define AUTH_REQ_PASSWORD    3    /* Password */
  #define AUTH_REQ_CRYPT        4    /* crypt password */
  #define AUTH_REQ_MD5        5    /* md5 password */
+ #define AUTH_REQ_SCM_CREDS    6    /* transfer SCM credentials */

  typedef uint32 AuthRequest;

Index: src/interfaces/libpq/fe-auth.c
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/interfaces/libpq/fe-auth.c,v
retrieving revision 1.50
diff -c -r1.50 fe-auth.c
*** src/interfaces/libpq/fe-auth.c    2001/08/15 21:08:21    1.50
--- src/interfaces/libpq/fe-auth.c    2001/08/16 14:56:49
***************
*** 40,50 ****
--- 40,57 ----
  #else
  #include <unistd.h>
  #include <fcntl.h>
+ #ifdef SCM_CREDS
+ #include <sys/uio.h>            /* for struct iovec */
+ #include <sys/ucred.h>
+ #include <errno.h>
+ #endif
  #include <sys/param.h>            /* for MAXHOSTNAMELEN on most */
  #ifndef  MAXHOSTNAMELEN
  #include <netdb.h>                /* for MAXHOSTNAMELEN on some */
  #endif
  #include <pwd.h>
+ #include <sys/types.h>
+ #include <sys/socket.h>            /* for SCM_CREDS */
  #endif

  #ifdef HAVE_CRYPT_H
***************
*** 432,437 ****
--- 439,490 ----

  #endif     /* KRB5 */

+ #ifdef SCM_CREDS
+ static int
+ pg_local_sendauth(char *PQerrormsg, PGconn *conn)
+ {
+     char buf;
+     struct iovec iov;
+     struct {
+         struct cmsghdr hdr;
+         /* We don't pass the credentials structure.   Kernel fills it in. */
+     } cmsg;
+     struct msghdr msg;
+
+     /*
+      * The backend doesn't care what we send here, but it wants
+      * exactly one character to force recvmsg() to block and wait
+      * for us.
+      */
+     buf = '\0';
+     iov.iov_base = &buf;
+     iov.iov_len = 1;
+
+     cmsg.hdr.cmsg_len = sizeof cmsg;
+     cmsg.hdr.cmsg_level = SOL_SOCKET;
+     cmsg.hdr.cmsg_type = SCM_CREDS;
+     /*
+      * cmsg.cred will get filled in with the correct information
+      * by the kernel when this message is sent.
+      */
+
+     msg.msg_name = NULL;
+     msg.msg_namelen = 0;
+     msg.msg_iov = &iov;
+     msg.msg_iovlen = 1;
+     msg.msg_control = &cmsg;
+     msg.msg_controllen = sizeof cmsg;
+     msg.msg_flags = 0;
+
+     if (sendmsg(conn->sock, &msg, 0) == -1) {
+         snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+              "pg_local_sendauth: sendmsg: %s\n", strerror(errno));
+         return STATUS_ERROR;
+     }
+     return STATUS_OK;
+ }
+ #endif
+
  static int
  pg_password_sendauth(PGconn *conn, const char *password, AuthRequest areq)
  {
***************
*** 442,447 ****
--- 495,504 ----

      switch (areq)
      {
+         case AUTH_REQ_PASSWORD:
+             /* discard const so we can assign it */
+             crypt_pwd = (char *)password;
+             break;
          case AUTH_REQ_CRYPT:
              crypt_pwd = crypt(password, conn->salt);
              break;
***************
*** 472,482 ****
                  break;
              }
          default:
!             /* discard const so we can assign it */
!             crypt_pwd = (char *)password;
!             break;
      }
-
      ret = pqPacketSend(conn, crypt_pwd, strlen(crypt_pwd) + 1);
      if (areq == AUTH_REQ_MD5)
          free(crypt_pwd);
--- 529,536 ----
                  break;
              }
          default:
!             return STATUS_ERROR;
      }
      ret = pqPacketSend(conn, crypt_pwd, strlen(crypt_pwd) + 1);
      if (areq == AUTH_REQ_MD5)
          free(crypt_pwd);
***************
*** 549,554 ****
--- 603,620 ----
                  return STATUS_ERROR;
              }
              break;
+
+         case AUTH_REQ_SCM_CREDS:
+ #ifdef SCM_CREDS
+             if (pg_local_sendauth(PQerrormsg, conn) != STATUS_OK)
+                 return STATUS_ERROR;
+ #else
+             snprintf(PQerrormsg, PQERRORMSG_LENGTH,
+                      libpq_gettext("SCM_CRED authentication method not supported\n"));
+             return STATUS_ERROR;
+ #endif
+             break;
+
          default:
              snprintf(PQerrormsg, PQERRORMSG_LENGTH,
                       libpq_gettext("authentication method %u not supported\n"), areq);
Index: src/interfaces/odbc/connection.c
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/interfaces/odbc/connection.c,v
retrieving revision 1.33
diff -c -r1.33 connection.c
*** src/interfaces/odbc/connection.c    2001/08/15 18:42:16    1.33
--- src/interfaces/odbc/connection.c    2001/08/16 14:56:50
***************
*** 722,727 ****
--- 722,732 ----
                              self->errornumber = CONN_AUTH_TYPE_UNSUPPORTED;
                              return 0;

+                         case AUTH_REQ_SCM_CREDS:
+                             self->errormsg = "Unix socket credential authentication not supported";
+                             self->errornumber = CONN_AUTH_TYPE_UNSUPPORTED;
+                             return 0;
+
                          default:
                              self->errormsg = "Unknown authentication type";
                              self->errornumber = CONN_AUTH_TYPE_UNSUPPORTED;
Index: src/interfaces/odbc/connection.h
===================================================================
RCS file: /home/projects/pgsql/cvsroot/pgsql/src/interfaces/odbc/connection.h,v
retrieving revision 1.25
diff -c -r1.25 connection.h
*** src/interfaces/odbc/connection.h    2001/08/15 18:42:16    1.25
--- src/interfaces/odbc/connection.h    2001/08/16 14:56:52
***************
*** 94,99 ****
--- 94,100 ----
  #define AUTH_REQ_PASSWORD                            3
  #define AUTH_REQ_CRYPT                                4
  #define AUTH_REQ_MD5                                5
+ #define AUTH_REQ_SCM_CREDS                            6

  /*    Startup Packet sizes */
  #define SM_DATABASE                                    64
RECV(2)            BSD Programmer's Manual            RECV(2)

NAME
     recv, recvfrom, recvmsg - receive a message from a socket

SYNOPSIS
     #include <sys/types.h>
     #include <sys/socket.h>

     ssize_t
     recv(int s, void *buf, size_t len, int flags);

     ssize_t
     recvfrom(int s, void *buf, size_t len, int flags, struct sockaddr *from,
         socklen_t *fromlen);

     ssize_t
     recvmsg(int s, struct msghdr *msg, int flags);

DESCRIPTION
     The recvfrom() and recvmsg() calls are used to receive messages from a
     socket, and may be used to receive data on a socket whether or not it is
     connection-oriented.

     If from is non-null, and the socket is not connection-oriented, the
     source address of the message is filled in.  The fromlen pointer refers
     to a value-result parameter; it should initially contain the amount of
     space pointed to by from; on return that location will contain the actual
     length (in bytes) of the address returned.    If the buffer provided is too
     small, the name is truncated and the full size is returned in the loca-
     tion to which fromlen points.  If from is null, the value pointed to by
     fromlen is not modified.  Otherwise, if the socket is connection-orient-
     ed, the address buffer will not be modified, and the value pointed to by
     fromlen will be set to zero.

     The recv() call is normally used only on a connected socket (see
     connect(2))  and is identical to recvfrom() with a nil from parameter.
     As it is redundant, it may not be supported in future releases.

     All three routines return the length of the message on successful comple-
     tion.  If a message is too long to fit in the supplied buffer, excess
     bytes may be discarded depending on the type of socket the message is re-
     ceived from (see socket(2)).

     If no messages are available at the socket, the receive call waits for a
     message to arrive, unless the socket is nonblocking (see fcntl(2))    in
     which case the value -1 is returned and the external variable errno set
     to EAGAIN. The receive calls normally return any data available, up to
     the requested amount, rather than waiting for receipt of the full amount
     requested; this behavior is affected by the socket-level options
     SO_RCVLOWAT and SO_RCVTIMEO described in getsockopt(2).

     The select(2) call may be used to determine when more data arrive.

     The flags argument to a recv call is formed by or'ing one or more of the
     values:

       MSG_OOB    process out-of-band data
       MSG_PEEK    peek at incoming message
       MSG_WAITALL    wait for full request or error

     The MSG_OOB flag requests receipt of out-of-band data that would not be
     received in the normal data stream.  Some protocols place expedited data
     at the head of the normal data queue, and thus this flag cannot be used
     with such protocols.  The MSG_PEEK flag causes the receive operation to
     return data from the beginning of the receive queue without removing that
     data from the queue.  Thus, a subsequent receive call will return the
     same data.    The MSG_WAITALL flag requests that the operation block until
     the full request is satisfied.  However, the call may still return less
     data than requested if a signal is caught, an error or disconnect occurs,
     or the next data to be received is of a different type than that re-
     turned.

     The recvmsg() call uses a msghdr structure to minimize the number of di-
     rectly supplied parameters.  This structure has the following form, as
     defined in <sys/socket.h>:

     struct msghdr {
         caddr_t msg_name;    /* optional address */
         u_int   msg_namelen;    /* size of address */
         struct  iovec *msg_iov; /* scatter/gather array */
         u_int   msg_iovlen;     /* # elements in msg_iov */
         caddr_t msg_control;    /* ancillary data, see below */
         u_int   msg_controllen; /* ancillary data buffer len */
         int     msg_flags;    /* flags on received message */
     };

     If msg_name is non-null, and the socket is not connection-oriented, the
     source address of the message is filled in.  The amount of space avail-
     able for the address is provided by msg_namelen, which is modified on re-
     turn to reflect the length of the stored address.    If the buffer is too
     small, the address is truncated; this is indicated when msg_namelen is
     less than the length embedded in the address (sa_len). If msg_name is
     null, msg_namelen is not modified.    Otherwise, if the socket is connec-
     tion-oriented, the address buffer will not be modified, and msg_namelen
     will be set to zero.

     Msg_iov and msg_iovlen describe scatter gather locations, as discussed in
     read(2).  Msg_control, which has length msg_controllen, points to a
     buffer for other protocol control related messages or other miscellaneous
     ancillary data.  The messages are of the form:

     struct cmsghdr {
         u_int   cmsg_len;    /* data byte count, including hdr */
         int     cmsg_level;     /* originating protocol */
         int     cmsg_type;    /* protocol-specific type */
     /* followed by
         u_char  cmsg_data[]; */
     };

     As an example, one could use this to learn of changes in the data-stream
     in XNS/SPP, or in ISO, to obtain user-connection-request data by request-
     ing a recvmsg with no data buffer provided immediately after an accept()
     call.

     Open file descriptors are now passed as ancillary data for AF_LOCAL do-
     main sockets, with cmsg_level set to SOL_SOCKET and cmsg_type set to
     SCM_RIGHTS.

     The msg_flags field is set on return according to the message received.
     MSG_EOR indicates end-of-record; the data returned completed a record
     (generally used with sockets of type SOCK_SEQPACKET). MSG_TRUNC indicates
     that the trailing portion of a datagram was discarded because the data-
     gram was larger than the buffer supplied.    MSG_CTRUNC indicates that some
     control data were discarded due to lack of space in the buffer for ancil-
     lary data.    MSG_OOB is returned to indicate that expedited or out-of-band
     data were received.

RETURN VALUES
     These calls return the number of bytes received, or -1 if an error oc-
     curred.

EXAMPLES
     The following code is an example of parsing the control information re-
     turned in the msg_control field.  This example shows how to parse the
     control messages for a localdomain(4) socket to obtain passed file de-
     scriptors and the sender's credentials.

     #include <sys/param.h>
     #include <sys/socket.h>
     #include <sys/ucred.h>

     struct msghdr msghdr;
     struct cmsghdr *cm;
     struct fcred *fc;    /* Pointer to the credentials */
     int fdcnt;        /* The number of file descriptors passed */
     int *fds;        /* The passed array of file descriptors */

     #define ENOUGH_CMSG(p, size)    ((p)->cmsg_len >= ((size) + sizeof(*(p))))

     fc = NULL;
     fdcnt = 0;
     fds = NULL;

     if (msghdr.msg_controllen >= sizeof (struct cmsghdr) &&
     (msghdr.msg_flags & MSG_CTRUNC) == 0) {

         for (cm = CMSG_FIRSTHDR(&msghdr);
         cm != NULL && cm->cmsg_len >= sizeof(*cm);
         cm = CMSG_NXTHDR(&msghdr, cm)) {

             if (cm->cmsg_level != SOL_SOCKET)
                 continue;

             switch (cm->cmsg_type) {
             case SCM_RIGHTS:
                 fdcnt = (cm->cmsg_len - sizeof(*cm)) / sizeof(int);
                 fds = (int *)CMSG_DATA(cm);
                 break;

             case SCM_CREDS:
                 if (ENOUGH_CMSG(cm, sizeof(*fc)))
                     fc = (struct fcred *)CMSG_DATA(cm);
                 break;
             }
         }
     }

ERRORS
     The calls fail if:

     [EBADF]    The argument s is an invalid descriptor.

     [ENOTCONN]    The socket is associated with a connection-oriented protocol
         and has not been connected (see connect(2) and accept(2)).

     [ENOTSOCK]    The argument s does not refer to a socket.

     [EAGAIN]    The socket is marked non-blocking, and the receive operation
         would block, or a receive timeout had been set, and the time-
         out expired before data were received.

     [EINTR]    The receive was interrupted by delivery of a signal before
         any data were available.

     [EFAULT]    The receive buffer pointer(s) point outside the process's ad-
         dress space.

SEE ALSO
     fcntl(2),    read(2),  select(2),  getsockopt(2),  socket(2),  ip(4),  lo-
     cal(4)

HISTORY
     The recv function call appeared in 4.2BSD.

4.3-Reno Berkeley Distribution February 21, 1994                 4

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