* Overriding "builtin"
@ 2022-08-12 1:18 Zach Riggle
2022-08-12 2:24 ` Đoàn Trần Công Danh
0 siblings, 1 reply; 14+ messages in thread
From: Zach Riggle @ 2022-08-12 1:18 UTC (permalink / raw)
To: Zsh Users
[-- Attachment #1: Type: text/plain, Size: 317 bytes --]
I recently learned that 'builtin' can be overridden with a function. Neat
for some silly tricks!
However, is there a way to save / restore 'builtin' such that it can be
restored?
All that I can think of is 'unfunction builtin', but 'unfunction' itself
can be overridden with a function.
Any ideas?
*Zach Riggle*
[-- Attachment #2: Type: text/html, Size: 629 bytes --]
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 1:18 Overriding "builtin" Zach Riggle
@ 2022-08-12 2:24 ` Đoàn Trần Công Danh
2022-08-12 7:12 ` Daniel Shahaf
0 siblings, 1 reply; 14+ messages in thread
From: Đoàn Trần Công Danh @ 2022-08-12 2:24 UTC (permalink / raw)
To: Zach Riggle; +Cc: Zsh Users
On 2022-08-11 20:18:49-0500, Zach Riggle <zachriggle@gmail.com> wrote:
> I recently learned that 'builtin' can be overridden with a function. Neat
> for some silly tricks!
>
> However, is there a way to save / restore 'builtin' such that it can be
> restored?
>
> All that I can think of is 'unfunction builtin', but 'unfunction' itself
> can be overridden with a function.
You can run original builtin with "builtin".
e.g.:
echo() { printf '++%s\n' "$@"; }
echo this will run function
builtin echo this will run builtin
--
Danh
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 2:24 ` Đoàn Trần Công Danh
@ 2022-08-12 7:12 ` Daniel Shahaf
2022-08-12 7:57 ` Stephane Chazelas
2022-08-12 13:54 ` Thomas Lauer
0 siblings, 2 replies; 14+ messages in thread
From: Daniel Shahaf @ 2022-08-12 7:12 UTC (permalink / raw)
To: Đoàn Trần Công Danh, Zach Riggle; +Cc: Zsh Users
Đoàn Trần Công Danh wrote on Fri, 12 Aug 2022 02:24 +00:00:
> On 2022-08-11 20:18:49-0500, Zach Riggle <zachriggle@gmail.com> wrote:
>> I recently learned that 'builtin' can be overridden with a function. Neat
>> for some silly tricks!
>>
>> However, is there a way to save / restore 'builtin' such that it can be
>> restored?
>>
>> All that I can think of is 'unfunction builtin', but 'unfunction' itself
>> can be overridden with a function.
>
«unset 'functions[unfunction]'», provided (zsh/parameter is available
and) someone hasn't created an unset() function as well.
> You can run original builtin with "builtin".
>
> e.g.:
>
> echo() { printf '++%s\n' "$@"; }
> echo this will run function
> builtin echo this will run builtin
No, he can't, because in his case that'd be a bottomless recursive call
(= an infinite loop).
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 7:12 ` Daniel Shahaf
@ 2022-08-12 7:57 ` Stephane Chazelas
2022-08-12 18:42 ` Lawrence Velázquez
2022-08-12 13:54 ` Thomas Lauer
1 sibling, 1 reply; 14+ messages in thread
From: Stephane Chazelas @ 2022-08-12 7:57 UTC (permalink / raw)
To: Daniel Shahaf
Cc: Đoàn Trần Công Danh, Zach Riggle, Zsh Users
On 2022-08-12 08:12, Daniel Shahaf wrote:
[...]
> «unset 'functions[unfunction]'», provided (zsh/parameter is available
> and) someone hasn't created an unset() function as well.
[...]
Or the standard "unset -f builtin"
Or functions=()
(or exec zsh -f)
Or
builtin() {
echo my builtin wrapper
set -o localoptions -o posixbuiltins
command builtin "$@"
}
(though that affects the behaviour of the builtin called by builtin.
--
Stephane
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 7:12 ` Daniel Shahaf
2022-08-12 7:57 ` Stephane Chazelas
@ 2022-08-12 13:54 ` Thomas Lauer
2022-08-12 15:41 ` Bart Schaefer
1 sibling, 1 reply; 14+ messages in thread
From: Thomas Lauer @ 2022-08-12 13:54 UTC (permalink / raw)
To: Daniel Shahaf; +Cc: ?oàn Tr?n Công Danh, Zach Riggle, Zsh Users
From: "Daniel Shahaf" <d.s@daniel.shahaf.name>
Date: Fri, 12 Aug 2022 07:12:56 +0000
> ?oàn Tr?n Công Danh wrote on Fri, 12 Aug 2022 02:24 +00:00:
> > On 2022-08-11 20:18:49-0500, Zach Riggle <zachriggle@gmail.com> wrote:
> >> I recently learned that 'builtin' can be overridden with a function. Neat
> >> for some silly tricks!
> >>
> >> However, is there a way to save / restore 'builtin' such that it can be
> >> restored?
> >>
> >> All that I can think of is 'unfunction builtin', but 'unfunction' itself
> >> can be overridden with a function.
> >
>
> «unset 'functions[unfunction]'», provided (zsh/parameter is available
> and) someone hasn't created an unset() function as well.
>
> > You can run original builtin with "builtin".
> >
> > e.g.:
> >
> > echo() { printf '++%s\n' "$@"; }
> > echo this will run function
> > builtin echo this will run builtin
>
> No, he can't, because in his case that'd be a bottomless recursive call
> (= an infinite loop).
Hm... this works here as I'd expect, but since you said "in his case"
there may be something that turns that into a non-terminating recursion
just for Zach's case. But what? (Always eager to learn something :-/ )
Tom
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 13:54 ` Thomas Lauer
@ 2022-08-12 15:41 ` Bart Schaefer
2022-08-12 16:07 ` Thomas Lauer
0 siblings, 1 reply; 14+ messages in thread
From: Bart Schaefer @ 2022-08-12 15:41 UTC (permalink / raw)
To: Thomas Lauer; +Cc: Zsh Users
On Fri, Aug 12, 2022 at 6:54 AM Thomas Lauer <thomas.lauer@virgin.net> wrote:
>
> Hm... this works here as I'd expect, but since you said "in his case"
> there may be something that turns that into a non-terminating recursion
> just for Zach's case. But what? (Always eager to learn something :-/ )
Zach's case is that "builtin" is itself a function.
builtin() { echo HA HA no builtins here; "$@" }
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 15:41 ` Bart Schaefer
@ 2022-08-12 16:07 ` Thomas Lauer
0 siblings, 0 replies; 14+ messages in thread
From: Thomas Lauer @ 2022-08-12 16:07 UTC (permalink / raw)
To: Bart Schaefer; +Cc: Zsh Users
----original message----
From: Bart Schaefer <schaefer@brasslantern.com>
Date: Fri, 12 Aug 2022 08:41:25 -0700
> On Fri, Aug 12, 2022 at 6:54 AM Thomas Lauer <thomas.lauer@virgin.net> wrote:
> >
> > Hm... this works here as I'd expect, but since you said "in his case"
> > there may be something that turns that into a non-terminating recursion
> > just for Zach's case. But what? (Always eager to learn something :-/ )
>
> Zach's case is that "builtin" is itself a function.
>
> builtin() { echo HA HA no builtins here; "$@" }
Got it. THX Tom
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 7:57 ` Stephane Chazelas
@ 2022-08-12 18:42 ` Lawrence Velázquez
2022-08-12 19:33 ` Zach Riggle
0 siblings, 1 reply; 14+ messages in thread
From: Lawrence Velázquez @ 2022-08-12 18:42 UTC (permalink / raw)
To: Zach Riggle
Cc: Stephane Chazelas, Daniel Shahaf,
Đoàn Trần Công Danh, zsh-users
On Fri, Aug 12, 2022, at 3:57 AM, Stephane Chazelas wrote:
> On 2022-08-12 08:12, Daniel Shahaf wrote:
> [...]
>> «unset 'functions[unfunction]'», provided (zsh/parameter is available
>> and) someone hasn't created an unset() function as well.
> [...]
>
> Or the standard "unset -f builtin"
>
> Or functions=()
>
> (or exec zsh -f)
>
> Or
>
> builtin() {
> echo my builtin wrapper
> set -o localoptions -o posixbuiltins
> command builtin "$@"
> }
Or ''unhash -f builtin''.
I (perhaps overzealously) interpreted the original question as
asking for a method that is impervious to interference from *any*
function (and maybe alias?) definition. But if you've broken your
shell so hard that *none* of these suggestions works, then, as they
say in the IRC channel, you get to keep the pieces.
--
vq
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 18:42 ` Lawrence Velázquez
@ 2022-08-12 19:33 ` Zach Riggle
2022-08-12 20:35 ` Lawrence Velázquez
2022-08-12 20:54 ` Bart Schaefer
0 siblings, 2 replies; 14+ messages in thread
From: Zach Riggle @ 2022-08-12 19:33 UTC (permalink / raw)
To: Lawrence Velázquez
Cc: Stephane Chazelas, Daniel Shahaf,
Đoàn Trần Công Danh, zsh-users
[-- Attachment #1: Type: text/plain, Size: 1180 bytes --]
Wouldn't the above also break for this?
function unhash() { ... }
It would be nice if we could add a feature such that the "builtin"
identifier cannot be overloaded.
*Zach Riggle*
On Fri, Aug 12, 2022 at 1:43 PM Lawrence Velázquez <larryv@zsh.org> wrote:
> On Fri, Aug 12, 2022, at 3:57 AM, Stephane Chazelas wrote:
> > On 2022-08-12 08:12, Daniel Shahaf wrote:
> > [...]
> >> «unset 'functions[unfunction]'», provided (zsh/parameter is available
> >> and) someone hasn't created an unset() function as well.
> > [...]
> >
> > Or the standard "unset -f builtin"
> >
> > Or functions=()
> >
> > (or exec zsh -f)
> >
> > Or
> >
> > builtin() {
> > echo my builtin wrapper
> > set -o localoptions -o posixbuiltins
> > command builtin "$@"
> > }
>
> Or ''unhash -f builtin''.
>
> I (perhaps overzealously) interpreted the original question as
> asking for a method that is impervious to interference from *any*
> function (and maybe alias?) definition. But if you've broken your
> shell so hard that *none* of these suggestions works, then, as they
> say in the IRC channel, you get to keep the pieces.
>
> --
> vq
>
[-- Attachment #2: Type: text/html, Size: 1886 bytes --]
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 19:33 ` Zach Riggle
@ 2022-08-12 20:35 ` Lawrence Velázquez
2022-08-12 20:54 ` Bart Schaefer
1 sibling, 0 replies; 14+ messages in thread
From: Lawrence Velázquez @ 2022-08-12 20:35 UTC (permalink / raw)
To: Zach Riggle
Cc: Stephane Chazelas, Daniel Shahaf,
Đoàn Trần Công Danh, zsh-users
On Fri, Aug 12, 2022, at 3:33 PM, Zach Riggle wrote:
> Wouldn't the above also break for this?
>
> function unhash() { ... }
Yes. I did not mean to imply that my suggestion was bulletproof,
only to opine that seeking such a method is a fool's errand. You
can take reasonable precautions, but at some point you are tilting
at windmills.
> It would be nice if we could add a feature such that the "builtin"
> identifier cannot be overloaded.
I think this is a solution in search of a problem.
--
vq
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 19:33 ` Zach Riggle
2022-08-12 20:35 ` Lawrence Velázquez
@ 2022-08-12 20:54 ` Bart Schaefer
2022-08-29 20:42 ` Zach Riggle
1 sibling, 1 reply; 14+ messages in thread
From: Bart Schaefer @ 2022-08-12 20:54 UTC (permalink / raw)
To: Zach Riggle; +Cc: zsh-users
On Fri, Aug 12, 2022 at 12:33 PM Zach Riggle <zachriggle@gmail.com> wrote:
>
> It would be nice if we could add a feature such that the "builtin" identifier cannot be overloaded.
This isn't really feasible, given that we have e.g. "disable builtin"
and "alias builtin=...".
That does point out that another approach to bypassing the function is
disable -f builtin
which is pretty nice in that it leaves the function defined but
inaccessible. Of course one can still "disable disable" as well.
I can't imagine why anyone would do this, but of course
disable -rm \*
disable -m \*
leaves the shell able to only to execute pipelines built from external
commands. Preceded with a few "alias -g" of separators, you end up
limited to simple external commands.
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-12 20:54 ` Bart Schaefer
@ 2022-08-29 20:42 ` Zach Riggle
2022-08-30 1:31 ` Bart Schaefer
2022-08-30 1:41 ` Bart Schaefer
0 siblings, 2 replies; 14+ messages in thread
From: Zach Riggle @ 2022-08-29 20:42 UTC (permalink / raw)
To: Bart Schaefer; +Cc: zsh-users
[-- Attachment #1: Type: text/plain, Size: 1766 bytes --]
Following up on this a bit, it seems that if your Zsh code is executing in
a malicious environment (e.g. has done "function /usr/bin/sudo() { echo lol
}") is to use a non-qualified path with the "=" prefix.
$ function /usr/bin/sudo { echo lol }
$ /usr/bin/sudo whoami
lol
$ =/usr/bin/sudo whoami
lol
$ =sudo whoami
root
Why does "=sudo" do the correct thing (assuming a sane $PATH, and executes
/usr/bin/sudo), but "=/usr/bin/sudo" does the wrong thing (i.e., execute
the function)?
Assume "builtin", "command", "exec", etc. have all been overwritten with
functions.
Since the environment is malicious, $PATH also cannot be trusted -- I
thought "=" might be a way to guarantee that an executable at a specific
absolute path does get executed instead of something else (alias, function,
autoloadable, etc) but it doesn't work when specifying the full path.
*Zach Riggle*
On Fri, Aug 12, 2022 at 3:54 PM Bart Schaefer <schaefer@brasslantern.com>
wrote:
> On Fri, Aug 12, 2022 at 12:33 PM Zach Riggle <zachriggle@gmail.com> wrote:
> >
> > It would be nice if we could add a feature such that the "builtin"
> identifier cannot be overloaded.
>
> This isn't really feasible, given that we have e.g. "disable builtin"
> and "alias builtin=...".
>
> That does point out that another approach to bypassing the function is
> disable -f builtin
> which is pretty nice in that it leaves the function defined but
> inaccessible. Of course one can still "disable disable" as well.
>
> I can't imagine why anyone would do this, but of course
>
> disable -rm \*
> disable -m \*
>
> leaves the shell able to only to execute pipelines built from external
> commands. Preceded with a few "alias -g" of separators, you end up
> limited to simple external commands.
>
[-- Attachment #2: Type: text/html, Size: 2992 bytes --]
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-29 20:42 ` Zach Riggle
@ 2022-08-30 1:31 ` Bart Schaefer
2022-08-30 1:41 ` Bart Schaefer
1 sibling, 0 replies; 14+ messages in thread
From: Bart Schaefer @ 2022-08-30 1:31 UTC (permalink / raw)
To: Zach Riggle; +Cc: zsh-users
On Mon, Aug 29, 2022 at 1:42 PM Zach Riggle <zachriggle@gmail.com> wrote:
>
> Why does "=sudo" do the correct thing (assuming a sane $PATH, and executes /usr/bin/sudo), but "=/usr/bin/sudo" does the wrong thing (i.e., execute the function)?
On my Ubuntu at least, =sudo is /bin/sudo not /usr/bin/sudo ... I
suspect if /usr/bin preceded /bin in $PATH, you would not see the
above behavior. I certainly can't reproduce similar behavior when
using a function named /bin/echo to attempt it.
^ permalink raw reply [flat|nested] 14+ messages in thread
* Re: Overriding "builtin"
2022-08-29 20:42 ` Zach Riggle
2022-08-30 1:31 ` Bart Schaefer
@ 2022-08-30 1:41 ` Bart Schaefer
1 sibling, 0 replies; 14+ messages in thread
From: Bart Schaefer @ 2022-08-30 1:41 UTC (permalink / raw)
To: Zach Riggle; +Cc: zsh-users
On Mon, Aug 29, 2022 at 1:42 PM Zach Riggle <zachriggle@gmail.com> wrote:
>
> Since the environment is malicious, $PATH also cannot be trusted -- I thought "=" might be a way to guarantee that an executable at a specific absolute path does get executed instead of something else (alias, function, autoloadable, etc) but it doesn't work when specifying the full path.
You can always use relative paths. E.g.
/../././../usr/bin/sudo
/usr/./bin/./sudo
etc.
it would be ... impractical ... to replace all possible combinations
of this with functions.
^ permalink raw reply [flat|nested] 14+ messages in thread
end of thread, other threads:[~2022-08-30 1:42 UTC | newest]
Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-08-12 1:18 Overriding "builtin" Zach Riggle
2022-08-12 2:24 ` Đoàn Trần Công Danh
2022-08-12 7:12 ` Daniel Shahaf
2022-08-12 7:57 ` Stephane Chazelas
2022-08-12 18:42 ` Lawrence Velázquez
2022-08-12 19:33 ` Zach Riggle
2022-08-12 20:35 ` Lawrence Velázquez
2022-08-12 20:54 ` Bart Schaefer
2022-08-29 20:42 ` Zach Riggle
2022-08-30 1:31 ` Bart Schaefer
2022-08-30 1:41 ` Bart Schaefer
2022-08-12 13:54 ` Thomas Lauer
2022-08-12 15:41 ` Bart Schaefer
2022-08-12 16:07 ` Thomas Lauer
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/zsh/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).