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Diffstat (limited to 'man2/setfsuid.2')
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1 files changed, 0 insertions, 127 deletions
diff --git a/man2/setfsuid.2 b/man2/setfsuid.2 deleted file mode 100644 index c6e75dafa..000000000 --- a/man2/setfsuid.2 +++ /dev/null @@ -1,127 +0,0 @@ -.\" Copyright (C) 1995, Thomas K. Dyas <tdyas@eden.rutgers.edu> -.\" and Copyright (C) 2013, 2019, Michael Kerrisk <mtk.manpages@gmail.com> -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.\" 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@gmail.com> -.\" Added notes on capability requirements -.\" -.TH setfsuid 2 (date) "Linux man-pages (unreleased)" -.SH NAME -setfsuid \- set user identity used for filesystem checks -.SH LIBRARY -Standard C library -.RI ( libc ", " \-lc ) -.SH SYNOPSIS -.nf -.B #include <sys/fsuid.h> -.P -.BI "[[deprecated]] int setfsuid(uid_t " fsuid ); -.fi -.SH DESCRIPTION -On Linux, a process has both a filesystem user ID and an effective user ID. -The (Linux-specific) filesystem user ID is used -for permissions checking when accessing filesystem objects, -while the effective user ID is used for various other kinds -of permissions checks (see -.BR credentials (7)). -.P -Normally, the value of the process's filesystem user ID -is the same as the value of its effective user ID. -This is so, because whenever a process's effective user ID is changed, -the kernel also changes the filesystem user ID to be the same as -the new value of the effective user ID. -A process can cause the value of its filesystem user ID to diverge -from its effective user ID by using -.BR setfsuid () -to change its filesystem user ID to the value given in -.IR fsuid . -.P -Explicit calls to -.BR setfsuid () -and -.BR setfsgid (2) -are (were) usually used only 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 (was) a security hole that can expose it to unwanted signals. -(However, this issue is historical; see below.) -.P -.BR setfsuid () -will succeed only if the caller is the superuser or if -.I fsuid -matches either the caller's real user ID, effective user ID, -saved set-user-ID, or current filesystem user ID. -.SH RETURN VALUE -On both success and failure, -this call returns the previous filesystem user ID of the caller. -.SH STANDARDS -Linux. -.SH HISTORY -Linux 1.2. -.\" Linux 1.1.44 -.\" and in libc since libc 4.7.6. -.P -At the time when this system call was introduced, one process -could send a signal to another process with the same effective user ID. -This meant that if a privileged process changed its effective user ID -for the purpose of file permission checking, -then it could become vulnerable to receiving signals -sent by another (unprivileged) process with the same user ID. -The filesystem user ID attribute was thus added to allow a process to -change its user ID for the purposes of file permission checking without -at the same time becoming vulnerable to receiving unwanted signals. -Since Linux 2.0, signal permission handling is different (see -.BR kill (2)), -with the result that a process can change its effective user ID -without being vulnerable to receiving signals from unwanted processes. -Thus, -.BR setfsuid () -is nowadays unneeded and should be avoided in new applications -(likewise for -.BR setfsgid (2)). -.P -The original Linux -.BR setfsuid () -system call supported only 16-bit user IDs. -Subsequently, Linux 2.4 added -.BR setfsuid32 () -supporting 32-bit IDs. -The glibc -.BR setfsuid () -wrapper function transparently deals with the variation across kernel versions. -.SS C library/kernel differences -In glibc 2.15 and earlier, -when the wrapper for this system call determines that the argument can't be -passed to the kernel without integer truncation (because the kernel -is old and does not support 32-bit user IDs), -it will return \-1 and set \fIerrno\fP to -.B EINVAL -without attempting -the system call. -.SH BUGS -No error indications of any kind are returned to the caller, -and the fact that both successful and unsuccessful calls return -the same value makes it impossible to directly determine -whether the call succeeded or failed. -Instead, the caller must resort to looking at the return value -from a further call such as -.I setfsuid(\-1) -(which will always fail), in order to determine if a preceding call to -.BR setfsuid () -changed the filesystem user ID. -At the very -least, -.B EPERM -should be returned when the call fails (because the caller lacks the -.B CAP_SETUID -capability). -.SH SEE ALSO -.BR kill (2), -.BR setfsgid (2), -.BR capabilities (7), -.BR credentials (7) |