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setfsuid.2: Clarify historical details and note that setfsuid() is obsolete 

Reported-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2013-08-09 09:15:03 +02:00
parent 9e3859ed2b
commit 18cc659761
1 changed files with 18 additions and 3 deletions
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21
man2/setfsuid.2
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@ -84,9 +84,24 @@ it will return \-1 and set \fIerrno\fP to
without attempting
the system call.
.LP
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.
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 privilged 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 change 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)).
The original Linux
.BR setfsuid ()