Index: head/lib/libc/sys/recv.2 =================================================================== --- head/lib/libc/sys/recv.2 (revision 313173) +++ head/lib/libc/sys/recv.2 (revision 313174) @@ -1,423 +1,376 @@ .\" Copyright (c) 1983, 1990, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)recv.2 8.3 (Berkeley) 2/21/94 .\" $FreeBSD$ .\" -.Dd August 18, 2016 +.Dd February 3, 2017 .Dt RECV 2 .Os .Sh NAME .Nm recv , .Nm recvfrom , .Nm recvmsg , .Nm recvmmsg .Nd receive message(s) from a socket .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/socket.h .Ft ssize_t .Fn recv "int s" "void *buf" "size_t len" "int flags" .Ft ssize_t .Fn recvfrom "int s" "void *buf" "size_t len" "int flags" "struct sockaddr * restrict from" "socklen_t * restrict fromlen" .Ft ssize_t .Fn recvmsg "int s" "struct msghdr *msg" "int flags" .Ft ssize_t .Fn recvmmsg "int s" "struct mmsghdr * restrict msgvec" "size_t vlen" "int flags" "const struct timespec * restrict timeout" .Sh DESCRIPTION The .Fn recvfrom , .Fn recvmsg , and .Fn recvmmsg system 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. .Pp If .Fa from is not a null pointer and the socket is not connection-oriented, the source address of the message is filled in. The .Fa fromlen argument is a value-result argument, initialized to the size of the buffer associated with .Fa from , and modified on return to indicate the actual size of the address stored there. .Pp The .Fn recv function is normally used only on a .Em connected socket (see .Xr connect 2 ) and is identical to .Fn recvfrom with a null pointer passed as its .Fa from argument. .Pp The .Fn recvmmsg function is used to receive multiple messages at a call. Their number is supplied by .Fa vlen . The messages are placed in the buffers described by .Fa msgvec vector, after reception. The size of each received message is placed in the .Fa msg_len field of each element of the vector. If .Fa timeout is NULL the call blocks until the data is available for each supplied message buffer. Otherwise it waits for data for the specified amount of time. If the timeout expired and there is no data received, a value 0 is returned. The .Xr ppoll 2 system call is used to implement the timeout mechanism, before first receive is performed. .Pp The .Fn recv , .Fn recvfrom and .Fn recvmsg return the length of the message on successful completion, whereas .Fn recvmmsg returns the number of received messages. 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 received from (see .Xr socket 2 ) . .Pp If no messages are available at the socket, the receive call waits for a message to arrive, unless the socket is non-blocking (see .Xr fcntl 2 ) in which case the value \-1 is returned and the global variable .Va errno is set to .Er EAGAIN . The receive calls except .Fn recvmmsg 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 .Dv SO_RCVLOWAT and .Dv SO_RCVTIMEO described in .Xr getsockopt 2 . The .Fn recvmmsg function implements this behaviour for each message in the vector. .Pp The .Xr select 2 system call may be used to determine when more data arrives. .Pp The .Fa flags argument to a .Fn recv function is formed by .Em or Ap ing one or more of the values: .Bl -column ".Dv MSG_CMSG_CLOEXEC" -offset indent .It Dv MSG_OOB Ta process out-of-band data .It Dv MSG_PEEK Ta peek at incoming message .It Dv MSG_WAITALL Ta wait for full request or error .It Dv MSG_DONTWAIT Ta do not block .It Dv MSG_CMSG_CLOEXEC Ta set received fds close-on-exec .It Dv MSG_WAITFORONE Ta do not block after receiving the first message (only for .Fn recvmmsg ) .El .Pp The .Dv 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 .Dv 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 .Dv 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 returned. The .Dv MSG_DONTWAIT flag requests the call to return when it would block otherwise. If no data is available, .Va errno is set to .Er EAGAIN . This flag is not available in strict .Tn ANSI or C99 compilation mode. The .Dv MSG_WAITFORONE flag sets MSG_DONTWAIT after the first message has been received. This flag is only relevant for .Fn recvmmsg . .Pp The .Fn recvmsg system call uses a .Fa msghdr structure to minimize the number of directly supplied arguments. This structure has the following form, as defined in .In sys/socket.h : .Bd -literal struct msghdr { void *msg_name; /* optional address */ socklen_t msg_namelen; /* size of address */ struct iovec *msg_iov; /* scatter/gather array */ int msg_iovlen; /* # elements in msg_iov */ void *msg_control; /* ancillary data, see below */ socklen_t msg_controllen;/* ancillary data buffer len */ int msg_flags; /* flags on received message */ }; .Ed .Pp Here .Fa msg_name and .Fa msg_namelen specify the destination address if the socket is unconnected; .Fa msg_name may be given as a null pointer if no names are desired or required. The .Fa msg_iov and .Fa msg_iovlen arguments describe scatter gather locations, as discussed in .Xr read 2 . The .Fa msg_control argument, which has length .Fa msg_controllen , points to a buffer for other protocol control related messages or other miscellaneous ancillary data. The messages are of the form: .Bd -literal struct cmsghdr { socklen_t cmsg_len; /* data byte count, including hdr */ int cmsg_level; /* originating protocol */ int cmsg_type; /* protocol-specific type */ /* followed by u_char cmsg_data[]; */ }; .Ed .Pp 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 requesting a .Fn recvmsg with no data buffer provided immediately after an .Fn accept system call. .Pp -Open file descriptors are now passed as ancillary data for +With .Dv AF_UNIX -domain sockets, with -.Fa cmsg_level -set to -.Dv SOL_SOCKET -and -.Fa cmsg_type -set to -.Dv SCM_RIGHTS . -The close-on-exec flag on received descriptors is set according to the -.Dv MSG_CMSG_CLOEXEC -flag passed to -.Fn recvmsg . -.Pp -Process credentials can also be passed as ancillary data for -.Dv AF_UNIX -domain sockets using a -.Fa cmsg_type -of -.Dv SCM_CREDS . -In this case, -.Fa cmsg_data -should be a structure of type -.Fa cmsgcred , -which is defined in -.In sys/socket.h -as follows: -.Bd -literal -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 or groups */ - gid_t cmcred_groups[CMGROUP_MAX]; /* groups */ -}; -.Ed -.Pp -If a sender supplies ancillary data with enough space for the above struct -tagged as -.Dv SCM_CREDS -control message type to the -.Fn sendmsg -system call, then kernel will fill in the credential information of the -sending process and deliver it to the receiver. -Since receiver usually has no control over a sender, this method of retrieving -credential information isn't reliable. -For reliable retrieval of remote side credentials it is advised to use the -.Dv LOCAL_CREDS -socket option on the receiving socket. +domain sockets, ancillary data can be used to pass file descriptors and +process credentials. See .Xr unix 4 for details. .Pp The .Fa msg_flags field is set on return according to the message received. .Dv MSG_EOR indicates end-of-record; the data returned completed a record (generally used with sockets of type .Dv SOCK_SEQPACKET ) . .Dv MSG_TRUNC indicates that the trailing portion of a datagram was discarded because the datagram was larger than the buffer supplied. .Dv MSG_CTRUNC indicates that some control data were discarded due to lack of space in the buffer for ancillary data. .Dv MSG_OOB is returned to indicate that expedited or out-of-band data were received. .Pp The .Fn recvmmsg system call uses the .Fa mmsghdr structure, defined as follows in the .In sys/socket.h header : .Bd -literal struct mmsghdr { struct msghdr msg_hdr; /* message header */ ssize_t msg_len; /* message length */ }; .Ed .Pp On data reception the .Fa msg_len field is updated to the length of the received message. .Sh RETURN VALUES These calls except .Fn recvmmsg return the number of bytes received. .Fn recvmmsg returns the number of messages received. A value of -1 is returned if an error occurred. .Sh ERRORS The calls fail if: .Bl -tag -width Er .It Bq Er EBADF The argument .Fa s is an invalid descriptor. .It Bq Er ECONNRESET The remote socket end is forcibly closed. .It Bq Er ENOTCONN The socket is associated with a connection-oriented protocol and has not been connected (see .Xr connect 2 and .Xr accept 2 ) . .It Bq Er ENOTSOCK The argument .Fa s does not refer to a socket. .It Bq Er EMSGSIZE The .Fn recvmsg system call was used to receive rights (file descriptors) that were in flight on the connection. However, the receiving program did not have enough free file descriptor slots to accept them. In this case the descriptors are closed, any pending data can be returned by another call to .Fn recvmsg . .It Bq Er EAGAIN The socket is marked non-blocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data were received. .It Bq Er EINTR The receive was interrupted by delivery of a signal before any data were available. .It Bq Er EFAULT The receive buffer pointer(s) point outside the process's address space. .El .Sh SEE ALSO .Xr fcntl 2 , .Xr getsockopt 2 , .Xr read 2 , .Xr select 2 , .Xr socket 2 , .Xr unix 4 .Sh HISTORY The .Fn recv function appeared in .Bx 4.2 . The .Fn recvmmsg function appeared in .Fx 11.0 . Index: head/share/man/man4/unix.4 =================================================================== --- head/share/man/man4/unix.4 (revision 313173) +++ head/share/man/man4/unix.4 (revision 313174) @@ -1,300 +1,363 @@ .\" Copyright (c) 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)unix.4 8.1 (Berkeley) 6/9/93 .\" $FreeBSD$ .\" -.Dd March 19, 2013 +.Dd February 3, 2017 .Dt UNIX 4 .Os .Sh NAME .Nm unix .Nd UNIX-domain protocol family .Sh SYNOPSIS .In sys/types.h .In sys/un.h .Sh DESCRIPTION The .Ux Ns -domain protocol family is a collection of protocols that provides local (on-machine) interprocess communication through the normal .Xr socket 2 mechanisms. The .Ux Ns -domain family supports the .Dv SOCK_STREAM , .Dv SOCK_SEQPACKET , and .Dv SOCK_DGRAM socket types and uses file system pathnames for addressing. .Sh ADDRESSING .Ux Ns -domain addresses are variable-length file system pathnames of at most 104 characters. The include file .In sys/un.h defines this address: .Bd -literal -offset indent struct sockaddr_un { u_char sun_len; u_char sun_family; char sun_path[104]; }; .Ed .Pp Binding a name to a .Ux Ns -domain socket with .Xr bind 2 causes a socket file to be created in the file system. This file is .Em not removed when the socket is closed \(em .Xr unlink 2 must be used to remove the file. .Pp The length of .Ux Ns -domain address, required by .Xr bind 2 and .Xr connect 2 , can be calculated by the macro .Fn SUN_LEN defined in .In sys/un.h . The .Va sun_path field must be terminated by a .Dv NUL character to be used with .Fn SUN_LEN , but the terminating .Dv NUL is .Em not part of the address. .Pp The .Ux Ns -domain protocol family does not support broadcast addressing or any form of .Dq wildcard matching on incoming messages. All addresses are absolute- or relative-pathnames of other .Ux Ns -domain sockets. Normal file system access-control mechanisms are also applied when referencing pathnames; e.g., the destination of a .Xr connect 2 or .Xr sendto 2 must be writable. -.Sh PASSING FILE DESCRIPTORS +.Sh CONTROL MESSAGES The .Ux Ns -domain sockets support the communication of .Ux -file descriptors through the use of the +file descriptors and process credentials through the use of the .Va msg_control field in the .Fa msg argument to .Xr sendmsg 2 and .Xr recvmsg 2 . -.Pp -Any valid descriptor may be sent in a message. -The file descriptor(s) to be passed are described using a +The items to be passed are described using a .Vt "struct cmsghdr" that is defined in the include file .In sys/socket.h . -The type of the message is +.Pp +To send file descriptors, the type of the message is .Dv 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. .Pp The received descriptor is a .Em duplicate of the sender's descriptor, as if it were created via .Li dup(fd) or .Li fcntl(fd, F_DUPFD_CLOEXEC, 0) depending on whether .Dv MSG_CMSG_CLOEXEC is passed in the .Xr 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. +.Pp +Credentials of the sending process can be transmitted explicitly using a +control message of type +.Dv SCM_CREDS +with a data portion of type +.Vt "struct cmsgcred" , +defined in +.In sys/socket.h +as follows: +.Bd -literal +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 */ +}; +.Ed +.Pp +The sender should pass a zeroed buffer which will be filled in by the system. +.Pp +The group list is truncated to at most +.Dv CMGROUP_MAX +GIDs. +.Pp +The process ID +.Fa cmcred_pid +should not be looked up (such as via the +.Dv 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. .Sh SOCKET OPTIONS .Tn UNIX domain sockets support a number of socket options which can be set with .Xr setsockopt 2 and tested with .Xr getsockopt 2 : .Bl -tag -width ".Dv LOCAL_CONNWAIT" .It Dv LOCAL_CREDS This option may be enabled on .Dv SOCK_DGRAM , .Dv SOCK_SEQPACKET , or a .Dv SOCK_STREAM socket. This option provides a mechanism for the receiver to -receive the credentials of the process as a +receive the credentials of the process calling +.Xr write 2 , +.Xr send 2 , +.Xr sendto 2 +or +.Xr sendmsg 2 +as a .Xr recvmsg 2 control message. The .Va msg_control field in the .Vt msghdr structure points to a buffer that contains a .Vt cmsghdr structure followed by a variable length .Vt sockcred structure, defined in .In sys/socket.h as follows: .Bd -literal 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 */ }; .Ed .Pp +The current implementation truncates the group list to at most +.Dv CMGROUP_MAX +groups. +.Pp The .Fn SOCKCREDSIZE macro computes the size of the .Vt sockcred structure for a specified number of groups. The .Vt cmsghdr fields have the following values: .Bd -literal cmsg_len = CMSG_LEN(SOCKCREDSIZE(ngroups)) cmsg_level = SOL_SOCKET cmsg_type = SCM_CREDS .Ed .Pp On .Dv SOCK_STREAM and .Dv SOCK_SEQPACKET sockets credentials are passed only on the first read from a socket, -then system clears the option on socket. +then the system clears the option on the socket. +.Pp +This option and the above explicit +.Vt "struct cmsgcred" +both use the same value +.Dv SCM_CREDS +but incompatible control messages. +If this option is enabled and the sender attached a +.Dv SCM_CREDS +control message with a +.Vt "struct cmsgcred" , +it will be discarded and a +.Vt "struct sockcred" +will be included. +.Pp +Many setuid programs will +.Xr write 2 +data at least partially controlled by the invoker, +such as error messages. +Therefore, a message accompanied by a particular +.Fa sc_euid +value should not be trusted as being from that user. .It Dv LOCAL_CONNWAIT Used with .Dv SOCK_STREAM sockets, this option causes the .Xr connect 2 function to block until .Xr accept 2 has been called on the listening socket. .It Dv LOCAL_PEERCRED Requested via .Xr getsockopt 2 on a .Dv SOCK_STREAM socket returns credentials of the remote side. These will arrive in the form of a filled in .Vt xucred structure, defined in .In sys/ucred.h as follows: .Bd -literal 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 */ }; .Ed The .Vt cr_version fields should be checked against .Dv XUCRED_VERSION define. .Pp The credentials presented to the server (the .Xr listen 2 caller) are those of the client when it called .Xr connect 2 ; the credentials presented to the client (the .Xr connect 2 caller) are those of the server when it called .Xr 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., .Xr connect 2 or .Xr listen 2 ) under different effective credentials. .Pp To reliably obtain peer credentials on a .Dv SOCK_DGRAM socket refer to the .Dv LOCAL_CREDS socket option. .El .Sh SEE ALSO .Xr connect 2 , .Xr dup 2 , .Xr fcntl 2 , .Xr getsockopt 2 , .Xr listen 2 , .Xr recvmsg 2 , .Xr sendto 2 , .Xr setsockopt 2 , .Xr socket 2 , .Xr intro 4 .Rs .%T "An Introductory 4.3 BSD Interprocess Communication Tutorial" .%B PS1 .%N 7 .Re .Rs .%T "An Advanced 4.3 BSD Interprocess Communication Tutorial" .%B PS1 .%N 8 .Re