o Remove meaningless PROTOCOLS section.
o Describe passing file descriptors as separate section. - Descriptors can be passed through any protocol of the UNIX family, not SOCK_STREAM and SOCK_SEQPACKET only. [1] o Describe socket options as separate section. - Move LOCAL_PEERCRED option to this section. - Describe struct xucred. - In LOCAL_CREDS section mention that credentials are passed only on the first read on non-datagram sockets. o Xref all mentioned system calls. Noticed by: Igor Sysoev [1]
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svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=243151
@ -32,7 +32,7 @@
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.\" @(#)unix.4 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd October 5, 2009
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.Dd November 16, 2012
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.Dt UNIX 4
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.Os
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.Sh NAME
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@ -123,20 +123,10 @@ of a
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or
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.Xr sendto 2
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must be writable.
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.Sh PROTOCOLS
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.Sh PASSING FILE DESCRIPTORS
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The
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.Ux Ns -domain
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protocol family is comprised of simple
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transport protocols that support the
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.Dv SOCK_STREAM ,
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.Dv SOCK_SEQPACKET ,
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and
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.Dv SOCK_DGRAM
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abstractions.
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.Dv SOCK_STREAM
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and
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.Dv SOCK_SEQPACKET
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sockets also support the communication of
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sockets support the communication of
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.Ux
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file descriptors through the use of the
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.Va msg_control
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@ -173,36 +163,7 @@ passed to a receiver.
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Descriptors that are awaiting delivery, or that are
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purposely not received, are automatically closed by the system
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when the destination socket is closed.
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.Pp
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The effective credentials (i.e., the user ID and group list) of a
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peer on a
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.Dv SOCK_STREAM
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socket may be obtained using the
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.Dv LOCAL_PEERCRED
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socket option.
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This may be used by a server to obtain and verify the credentials of
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its client, and vice versa by the client to verify the credentials
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of the server.
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These will arrive in the form of a filled in
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.Vt "struct xucred"
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(defined in
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.In sys/ucred.h ) .
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The credentials presented to the server (the
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.Xr listen 2
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caller) are those of the client when it called
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.Xr connect 2 ;
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the credentials presented to the client (the
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.Xr connect 2
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caller) are those of the server when it called
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.Xr listen 2 .
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This mechanism is reliable; there is no way for either party to influence
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the credentials presented to its peer except by calling the appropriate
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system call (e.g.,
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.Xr connect 2
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or
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.Xr listen 2 )
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under different effective credentials.
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.Pp
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.Sh SOCKET OPTIONS
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.Tn UNIX
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domain sockets support a number of socket options which can be set with
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.Xr setsockopt 2
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@ -256,6 +217,13 @@ cmsg_len = CMSG_LEN(SOCKCREDSIZE(ngroups))
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cmsg_level = SOL_SOCKET
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cmsg_type = SCM_CREDS
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.Ed
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.Pp
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On
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.Dv SOCK_STREAM
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and
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.Dv SOCK_SEQPACKET
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sockets credentials are passed only on the first read from a socket,
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then system clears the option on socket.
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.It Dv LOCAL_CONNWAIT
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Used with
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.Dv SOCK_STREAM
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@ -264,8 +232,62 @@ sockets, this option causes the
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function to block until
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.Xr accept 2
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has been called on the listening socket.
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.It Dv LOCAL_PEERCRED
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Requested via
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.Xr getsockopt 2
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on a
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.Dv SOCK_STREAM
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socket returns credentials of the remote side.
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These will arrive in the form of a filled in
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.Vt xucred
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structure, defined in
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.In sys/ucred.h
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as follows:
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.Bd -literal
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struct xucred {
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u_int cr_version; /* structure layout version */
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uid_t cr_uid; /* effective user id */
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short cr_ngroups; /* number of groups */
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gid_t cr_groups[XU_NGROUPS]; /* groups */
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};
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.Ed
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The
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.Vt cr_version
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fields should be checked against
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.Dv XUCRED_VERSION
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define.
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.Pp
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The credentials presented to the server (the
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.Xr listen 2
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caller) are those of the client when it called
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.Xr connect 2 ;
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the credentials presented to the client (the
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.Xr connect 2
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caller) are those of the server when it called
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.Xr listen 2 .
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This mechanism is reliable; there is no way for either party to influence
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the credentials presented to its peer except by calling the appropriate
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system call (e.g.,
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.Xr connect 2
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or
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.Xr listen 2 )
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under different effective credentials.
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.Pp
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To reliably obtain peer credentials on a
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.Dv SOCK_DGRAM
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socket refer to the
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.Dv LOCAL_CREDS
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socket option.
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.El
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.Sh SEE ALSO
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.Xr connect 2 ,
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.Xr dup 2 ,
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.Xr fcntl 2 ,
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.Xr getsockopt 2 ,
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.Xr listen 2 ,
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.Xr recvmsg 2 ,
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.Xr sendto 2 ,
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.Xr setsockopt 2 ,
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.Xr socket 2 ,
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.Xr intro 4
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.Rs
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