Name
setfsuid — set user identity used for file system
checks
Synopsis
int
setfsuid( |
uid_t |
fsuid); |
DESCRIPTION
The system call setfsuid()
sets the user ID that the Linux kernel uses to check for all
accesses to the file system. Normally, the value of
fsuid will shadow the
value of the effective user ID. In fact, whenever the
effective user ID is changed, fsuid will also be changed to
the new value of the effective user ID.
Explicit calls to setfsuid()
and setfsgid(2) are usually
only used by programs such as the Linux NFS server that need
to change what user and group ID is used for file access
without a corresponding change in the real and effective user
and group IDs. A change in the normal user IDs for a program
such as the NFS server is a security hole that can expose it
to unwanted signals. (But see below.)
setfsuid() will only succeed
if the caller is the superuser or if fsuid matches either the real
user ID, effective user ID, saved set-user-ID, or the current
value of fsuid.
RETURN VALUE
On success, the previous value of fsuid is returned. On error,
the current value of fsuid is returned.
CONFORMING TO
setfsuid() is Linux specific
and should not be used in programs intended to be portable.
It is present since Linux 1.1.44 and in libc since libc
4.7.6.
NOTES
When glibc determines that the argument is not a valid
user ID, it will return −1 and set errno to EINVAL without attempting the
system call.
Note that at the time this system call was introduced, a
process could send a signal to a process with the same
effective user ID. Today signal permission handling is
slightly different.
BUGS
No error messages of any kind are returned to the caller.
At the very least, EPERM
should be returned when the call fails (because the caller
lacks the CAP_SETUID
capability).
SEE ALSO
kill(2), setfsgid(2), capabilities(7), credentials(7)
Copyright (C) 1995, Thomas K. Dyas <tdyas@eden.rutgers.edu>
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manual page may be incorrect or out-of-date.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.
Created 1995-08-06 Thomas K. Dyas <tdyas@eden.rutgers.edu>
Modified 2000-07-01 aeb
Modified 2002-07-23 aeb
Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
Added notes on capability requirements
|
