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chroot.2: Minor fixes 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-06-16 13:20:47 +02:00
parent 3c4dfb62a5
commit ba9aa794c8
1 changed files with 9 additions and 7 deletions
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16
man2/chroot.2
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@ -73,27 +73,29 @@ capability) may call
.BR chroot (). .BR chroot ().
This call changes an ingredient in the pathname resolution process This call changes an ingredient in the pathname resolution process
and does nothing else. In particular, it is not intended to be used and does nothing else.
In particular, it is not intended to be used
for any kind of security purpose, neither to fully sandbox a process nor for any kind of security purpose, neither to fully sandbox a process nor
to restrict filesystem syscalls. In the past, to restrict filesystem system calls.
In the past,
.BR chroot () .BR chroot ()
has been used by daemons to restrict themselves prior to passing paths has been used by daemons to restrict themselves prior to passing paths
supplied by untrusted users into syscalls like supplied by untrusted users to system calls such as
.BR open (2). .BR open (2).
However, if a folder is moved out of the chroot directory, an attacker However, if a folder is moved out of the chroot directory, an attacker
can exploit that to get out of the chroot directory as well. The easiest can exploit that to get out of the chroot directory as well.
way to do that is to The easiest way to do that is to
.BR chdir (2) .BR chdir (2)
to the to-be-moved directory, wait for it to be moved out, then open a to the to-be-moved directory, wait for it to be moved out, then open a
path like ../../../etc/passwd. path like ../../../etc/passwd.
.\" This is how the "slightly trickier variation" works: .\" This is how the "slightly trickier variation" works:
.\" https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-014-2015.txt#L142 .\" https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-014-2015.txt#L142
A slightly A slightly
trickier variation also works under some circumstances if trickier variation also works under some circumstances if
.BR chdir (2) .BR chdir (2)
is not permitted. If a daemon allows a "chroot directory" to be specified, is not permitted.
If a daemon allows a "chroot directory" to be specified,
that usually means that if you want to prevent remote users from accessing that usually means that if you want to prevent remote users from accessing
files outside the chroot directory, you must ensure that folders are never files outside the chroot directory, you must ensure that folders are never
moved out of it. moved out of it.