patchgitk: use mktemp -d to avoid predictable temporary directories

> gitk uses a predictable ".gitk-tmp.$PID" pattern when generating
> a temporary directory.
> 
> Use "mktemp -d .gitk-tmp.XXXXXX" to harden gitk against someone
> seeding /tmp with files matching the pid pattern.
> 
> Signed-off-by: David Aguilar <davvid@gmail.com>

>gitk uses a predictable ".gitk-tmp.$PID" pattern when generating
>a temporary directory.
>
>Use "mktemp -d .gitk-tmp.XXXXXX" to harden gitk against someone
>seeding /tmp with files matching the pid pattern.
>
>Signed-off-by: David Aguilar <davvid@gmail.com>
>---
>This issue was brought up during the first review of the previous patch
>back in 2009.
>
>http://thread.gmane.org/gmane.comp.version-control.git/132609/focus=132748
>
>This is really [PATCH 2/2] and should be applied on top of my previous
>gitk patch.
>
> gitk | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/gitk b/gitk
>index 82293dd..dd2ff63 100755
>--- a/gitk
>+++ b/gitk
>@@ -3502,7 +3502,8 @@ proc gitknewtmpdir {} {
> 	} else {
> 	    set tmpdir $gitdir
> 	}
>-	set gitktmpdir [file join $tmpdir [format ".gitk-tmp.%s" [pid]]]
>+	set gitktmpformat [file join $tmpdir ".gitk-tmp.XXXXXX"]
>+	set gitktmpdir [exec mktemp -d $gitktmpformat]
> 	if {[catch {file mkdir $gitktmpdir} err]} {
> 	    error_popup "[mc "Error creating temporary directory %s:" $gitktmpdir] $err"
> 	    unset gitktmpdir

> David Aguilar <davvid@gmail.com> writes:
> >--- a/gitk
> >+++ b/gitk
> >@@ -3502,7 +3502,8 @@ proc gitknewtmpdir {} {
> > 	} else {
> > 	    set tmpdir $gitdir
> > 	}
> >-	set gitktmpdir [file join $tmpdir [format ".gitk-tmp.%s" [pid]]]
> >+	set gitktmpformat [file join $tmpdir ".gitk-tmp.XXXXXX"]
> >+	set gitktmpdir [exec mktemp -d $gitktmpformat]
> > 	if {[catch {file mkdir $gitktmpdir} err]} {
> > 	    error_popup "[mc "Error creating temporary directory %s:" $gitktmpdir] $err"
> > 	    unset gitktmpdir
> 
> This is a problem on Windows where we will not have mktemp. In Tcl 8.6
> the file command acquired a "file tempfile" command to help with this
> kind of issue (https://www.tcl.tk/man/tcl8.6/TclCmd/file.htm#M39) but
> for older versions we should probably stick with the existing pattern at
> least on Windows.

> On Sun, Jun 15, 2014 at 08:51:23AM +0100, Pat Thoyts wrote:
> > David Aguilar <davvid@gmail.com> writes:
> > >--- a/gitk
> > >+++ b/gitk
> > >@@ -3502,7 +3502,8 @@ proc gitknewtmpdir {} {
> > > 	} else {
> > > 	    set tmpdir $gitdir
> > > 	}
> > >-	set gitktmpdir [file join $tmpdir [format ".gitk-tmp.%s" [pid]]]
> > >+	set gitktmpformat [file join $tmpdir ".gitk-tmp.XXXXXX"]
> > >+	set gitktmpdir [exec mktemp -d $gitktmpformat]
> > > 	if {[catch {file mkdir $gitktmpdir} err]} {
> > > 	    error_popup "[mc "Error creating temporary directory %s:" $gitktmpdir] $err"
> > > 	    unset gitktmpdir
> > 
> > This is a problem on Windows where we will not have mktemp. In Tcl 8.6
> > the file command acquired a "file tempfile" command to help with this
> > kind of issue (https://www.tcl.tk/man/tcl8.6/TclCmd/file.htm#M39) but
> > for older versions we should probably stick with the existing pattern at
> > least on Windows.
> 
> The existing pattern is a security bug on Unix systems. MITRE (CWE-377)
> tells me that it is a vulnerability on Windows as well, so you'd
> probably want to come up with a better solution than the existing
> pattern.
> 
> You also probably want to request a CVE for this, which the Red Hat and
> Debian security teams can do for you if you like.  Distributions will
> likely want to issue security advisories for this.

> Hmm.. I guess what I could do is keep the old behavior (having gitk
> ignore TMPDIR) on Windows and only use the new code path on
> non-Windows.
> 
> That seems like it'd be the simplest implementation (no need to check
> versions) and the least harmful to existing users (avoids a tcl
> upgrade or mkdtemp installation for Windows users).

> David Aguilar <davvid@gmail.com> writes:
> 
> > Hmm.. I guess what I could do is keep the old behavior (having gitk ignore TMPDIR)
> > on Windows and only use the new code path on non-Windows.
> 
> Or perhaps attempt to create, catch error and then retry the old way?
> 
> Hopefully Windows folks do not have to worry about forgetting to
> update the codepath when they update their tcl/wish if you did it
> that way, no?

> David Aguilar <davvid@gmail.com> writes:
> 
>> gitk uses a predictable ".gitk-tmp.$PID" pattern when generating
>> a temporary directory.
>>
>> Use "mktemp -d .gitk-tmp.XXXXXX" to harden gitk against someone
>> seeding /tmp with files matching the pid pattern.
>>
>> Signed-off-by: David Aguilar <davvid@gmail.com>
>> ---
>> This issue was brought up during the first review of the previous patch
>> back in 2009.
>>
>> http://thread.gmane.org/gmane.comp.version-control.git/132609/focus=132748
>>
>> This is really [PATCH 2/2] and should be applied on top of my previous
>> gitk patch.
>>
>> gitk | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/gitk b/gitk
>> index 82293dd..dd2ff63 100755
>> --- a/gitk
>> +++ b/gitk
>> @@ -3502,7 +3502,8 @@ proc gitknewtmpdir {} {
>> 	} else {
>> 	    set tmpdir $gitdir
>> 	}
>> -	set gitktmpdir [file join $tmpdir [format ".gitk-tmp.%s" [pid]]]
>> +	set gitktmpformat [file join $tmpdir ".gitk-tmp.XXXXXX"]
>> +	set gitktmpdir [exec mktemp -d $gitktmpformat]
>> 	if {[catch {file mkdir $gitktmpdir} err]} {
>> 	    error_popup "[mc "Error creating temporary directory %s:" $gitktmpdir] $err"
>> 	    unset gitktmpdir
> 
> This is a problem on Windows where we will not have mktemp. In Tcl 8.6
> the file command acquired a "file tempfile" command to help with this
> kind of issue (https://www.tcl.tk/man/tcl8.6/TclCmd/file.htm#M39) but
> for older versions we should probably stick with the existing pattern at
> least on Windows.