From: Olga Kornievskaia <kolga@netapp.com>
To: <linux-fsdevel@vger.kernel.org>, <linux-nfs@vger.kernel.org>,
        <linux-api@vger.kernel.org>
Subject: [RFC 1/1] destroy_creds.2: new page documenting destroy_creds()
Date: Mon, 7 Aug 2017 17:23:53 -0400
Message-ID: <20170807212355.29127-3-kolga@netapp.com>
In-Reply-To: <20170807212355.29127-1-kolga@netapp.com>
References: <20170807212355.29127-1-kolga@netapp.com>
MIME-Version: 1.0
Content-Type: text/plain
Sender: linux-nfs-owner@vger.kernel.org

destroy_creds() is a new system call for destroying file system
credentials. This is usefulf for file systems that manage its
own security contexts that were bootstrapped via some user land
credentials (such as Kerberos).

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
---
 man2/destroy_creds.2 | 130 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 man2/destroy_creds.2

diff --git a/man2/destroy_creds.2 b/man2/destroy_creds.2
new file mode 100644
index 0000000..7b41c9d
--- /dev/null
+++ b/man2/destroy_creds.2
@@ -0,0 +1,130 @@
+.\"This manpage is Copyright (C) 2015 Olga Kornievskaia <kolga@Netapp.com>
+.\"
+.\" %%%LICENSE_START(VERBATIM)
+.\" Permission is granted to make and distribute verbatim copies of this
+.\" manual provided the copyright notice and this permission notice are
+.\" preserved on all copies.
+.\"
+.\" Permission is granted to copy and distribute modified versions of
+.\" this manual under the conditions for verbatim copying, provided that
+.\" the entire resulting derived work is distributed under the terms of
+.\" a permission notice identical to this one.
+.\"
+.\" Since the Linux kernel and libraries are constantly changing, this
+.\" manual page may be incorrect or out-of-date.  The author(s) assume
+.\" no responsibility for errors or omissions, or for damages resulting
+.\" from the use of the information contained herein.  The author(s) may
+.\" not have taken the same level of care in the production of this
+.\" manual, which is licensed free of charge, as they might when working
+.\" professionally.
+.\"
+.\" Formatted or processed versions of this manual, if unaccompanied by
+.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
+.\"
+.TH COPY 2 2017-08-07 "Linux" "Linux Programmer's Manual"
+.SH NAME
+destroy_creds \- destroy current user's file system credentials for a mount point
+.SH SYNOPSIS
+.nf
+.B #include <sys/syscall.h>
+.B #include <unistd.h>
+
+.BI "int destroy_creds(int " fd ");
+.fi
+.SH DESCRIPTION
+The
+.BR destroy ()
+system call performs destruction of file system credentials for the current
+user. It identifies the file system by the supplied file descriptor in
+.I fd
+that represents a mount point.
+
+.SH RETURN VALUE
+Upon successful completion,
+.BR destroy_creds ()
+will return 0.
+
+On error,
+.BR destroy_creds ()
+returns \-1 and
+.I errno
+is set to indicate the error.
+.SH ERRORS
+.TP
+.B EBADF
+.I fd
+file descriptor is not valid
+.TP
+.B EINVAL
+if the input file descriptor is not a directory
+.TP
+.B ENOENT
+no credentials found
+.TP
+.B EACCES
+unable to access credentials
+.TP
+.B ENOSYS
+file system does not implement destroy_creds() functionality
+.SH VERSIONS
+The
+.BR destroy_creds ()
+system call first appeared in Linux 4.1?.
+.SH CONFORMING TO
+The
+.BR destroy_creds ()
+system call is a nonstandard Linux extension.
+.SH NOTES
+
+.BR destroy_creds ()
+gives filesystems an opportunity to destroy credentials. For instance,
+NFS uses Kerberos credentials stored in Kerberos credential cache to
+create its security contexts that then are stored and managed by the
+kernel. Once the user logs out and destroys Kerberos credentials via
+kdestroy, NFS security contexts associate with that user are valid 
+until they expire. fslogout application such provided by the example
+allows the user driven credential destruction in the file system.
+
+.SH EXAMPLE
+.nf
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+
+static int
+destroy_creds(int fd)
+{
+    return syscall(__NR_destroy_creds, fd);
+}
+
+int
+main(int argc, char **argv)
+{
+    int fd, ret;
+
+    if (argc != 2) {
+        fprintf(stderr, "Usage: %s <mount point>\\n", argv[0]);
+        exit(EXIT_FAILURE);
+    }
+
+    fd = open(argv[1], O_DIRECTORY|O_RDONLY);
+    if (fd == \-1) {
+        perror("open (argv[1])");
+        exit(EXIT_FAILURE);
+    }
+
+    ret = destroy_creds(fd);
+    if (ret == \-1) {
+        perror("destroy_creds");
+        exit(EXIT_FAILURE);
+    }
+
+    close(fd);
+    exit(EXIT_SUCCESS);
+}
+.fi
-- 
1.8.3.1