threads / patch / 44350

patch: run-command.c

Subject: [BUG] [PATCH]: run-command.c

## tl;dr

4 messages between Oct 21, 2016 and Oct 21, 2016. Diffs are folded; open one to read it.

replies: 3people: 3as markdown or json

Duncan Roe· Oct 21, 2016, 05:50 UTC · lore

prepare_shell_cmd() executes /bin/sh with superfluous arguments on all but single-word shell commands.

For example, if .git/config has this alias (the sleep is to leave time to examine output from ps, &c.):

[alias]
	tryme = "!echo $PWD;sleep 600"
running "git tryme" in one console and checking what it does in another
--- 1st xterm

16:42:12$ git tryme /usr/src/git/.git echo $PWD;sleep 600: line 1: 2602 Terminated sleep 600 16:43:15$

--- 2nd xterm
16:42:06$ ps axf|grep -A2 trym[e]
 2599 pts/4    S+     0:00      \_ git tryme
 2601 pts/4    S+     0:00          \_ /bin/sh -c echo $PWD;sleep 600 echo $PWD;sleep 600
 2602 pts/4    S+     0:00              \_ sleep 600
16:42:45$ cat /proc/2601/cmdline | xargs -0 -n1 echo
/bin/sh
-c
echo $PWD;sleep 600
echo $PWD;sleep 600
16:43:04$ kill 2602
16:43:15$
---

There is an extra "-c" argument. This is caused by a missing "else", fixed by the appended patch,

Cheers ... Duncan.
----------8<-------------------
Show changes to run-command.c +2 −2
--- a/run-command.c
+++ b/run-command.c
@@ -182,8 +182,8 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
 		else
 			argv_array_pushf(out, "%s \"$@\"", argv[0]);
 	}
-
-	argv_array_pushv(out, argv);
+	else
+		argv_array_pushv(out, argv);
 	return out->argv;
 }
Jeff King· Oct 21, 2016, 09:00 UTC · re: Duncan Roe · lore

Re: [BUG] [PATCH]: run-command.c

On Fri, Oct 21, 2016 at 04:50:13PM +1100, Duncan Roe wrote:
Show 16 quoted lines
> For example, if .git/config has this alias (the sleep is to leave time to
> examine output from ps, &c.):
> 
> [alias]
> 	tryme = "!echo $PWD;sleep 600"
>
> [...]
> 16:42:06$ ps axf|grep -A2 trym[e]
>  2599 pts/4    S+     0:00      \_ git tryme
>  2601 pts/4    S+     0:00          \_ /bin/sh -c echo $PWD;sleep 600 echo $PWD;sleep 600
>  2602 pts/4    S+     0:00              \_ sleep 600
> 16:42:45$ cat /proc/2601/cmdline | xargs -0 -n1 echo
> /bin/sh
> -c
> echo $PWD;sleep 600
> echo $PWD;sleep 600

This duplicated argument is expected and normal. The arguments after "-c whatever" become positional parameters $0, $1, etc. The actual script arguments start at "$1", and "$0" is typically the "script name". So you have to stick some placeholder value in the "$0" slot, so that the sub-script can find the actual arguments. E.g., try:

  sh -c '
    for i in "$@"; do
      echo "got $i"
    done
  ' one two three
it will print only:
  got two
  got three
But if you stick a placeholder there, it works:
  sh -c '
    for i in "$@"; do
      echo "got $i"
    done
  ' placeholder one two three

The value of the placeholder does not matter to the shell. But it is accessible to the script inside via $0:

  sh -c '
    echo "\$0 = $0"
    echo "\$1 = $1"
    echo "\$2 = $2"
    echo "\$3 = $3"
  ' placeholder one two three

Since our script does not have a filename, we just stick the script contents there (which is really just a convention, and one I doubt anybody is really relying on, but there's no point in breaking it now).

Show 12 quoted lines
> --- a/run-command.c
> +++ b/run-command.c
> @@ -182,8 +182,8 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
>  		else
>  			argv_array_pushf(out, "%s \"$@\"", argv[0]);
>  	}
> -
> -	argv_array_pushv(out, argv);
> +	else
> +		argv_array_pushv(out, argv);
>  	return out->argv;
>  }

Try running "make test" with this. Lots of things break, because we are not sending the positional parameters to the shell script at all.

If we just cared about the positional parmeters, we _could_ do something like:

  if (argv[0]) {
	argv_array_push(out, "sh");
	argv_array_pushv(out, argv + 1);
  }

That would omit "$0" entirely when we have no positional parameters (and the shell generally fills in "sh" there itself), and provide a dummy "sh" value when we need to use it as a placeholder.

But again, there's no real value in breaking the existing convention.
-Peff
Duncan Roe· Oct 21, 2016, 11:07 UTC · re: Jeff King · lore

Re: [BUG] [PATCH]: run-command.c

On Fri, Oct 21, 2016 at 05:00:29AM -0400, Jeff King wrote:
Show 89 quoted lines
> On Fri, Oct 21, 2016 at 04:50:13PM +1100, Duncan Roe wrote:
>
> > For example, if .git/config has this alias (the sleep is to leave time to
> > examine output from ps, &c.):
> >
> > [alias]
> > 	tryme = "!echo $PWD;sleep 600"
> >
> > [...]
> > 16:42:06$ ps axf|grep -A2 trym[e]
> >  2599 pts/4    S+     0:00      \_ git tryme
> >  2601 pts/4    S+     0:00          \_ /bin/sh -c echo $PWD;sleep 600 echo $PWD;sleep 600
> >  2602 pts/4    S+     0:00              \_ sleep 600
> > 16:42:45$ cat /proc/2601/cmdline | xargs -0 -n1 echo
> > /bin/sh
> > -c
> > echo $PWD;sleep 600
> > echo $PWD;sleep 600
>
> This duplicated argument is expected and normal. The arguments after "-c
> whatever" become positional parameters $0, $1, etc. The actual script
> arguments start at "$1", and "$0" is typically the "script name".
> So you have to stick some placeholder value in the "$0" slot, so that
> the sub-script can find the actual arguments. E.g., try:
>
>   sh -c '
>     for i in "$@"; do
>       echo "got $i"
>     done
>   ' one two three
>
> it will print only:
>
>   got two
>   got three
>
> But if you stick a placeholder there, it works:
>
>   sh -c '
>     for i in "$@"; do
>       echo "got $i"
>     done
>   ' placeholder one two three
>
> The value of the placeholder does not matter to the shell. But it is
> accessible to the script inside via $0:
>
>   sh -c '
>     echo "\$0 = $0"
>     echo "\$1 = $1"
>     echo "\$2 = $2"
>     echo "\$3 = $3"
>   ' placeholder one two three
>
> Since our script does not have a filename, we just stick the script
> contents there (which is really just a convention, and one I doubt
> anybody is really relying on, but there's no point in breaking it now).
>
> > --- a/run-command.c
> > +++ b/run-command.c
> > @@ -182,8 +182,8 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv)
> >  		else
> >  			argv_array_pushf(out, "%s \"$@\"", argv[0]);
> >  	}
> > -
> > -	argv_array_pushv(out, argv);
> > +	else
> > +		argv_array_pushv(out, argv);
> >  	return out->argv;
> >  }
>
> Try running "make test" with this. Lots of things break, because we are
> not sending the positional parameters to the shell script at all.
>
> If we just cared about the positional parmeters, we _could_ do something
> like:
>
>   if (argv[0]) {
> 	argv_array_push(out, "sh");
> 	argv_array_pushv(out, argv + 1);
>   }
>
> That would omit "$0" entirely when we have no positional parameters (and
> the shell generally fills in "sh" there itself), and provide a dummy
> "sh" value when we need to use it as a placeholder.
>
> But again, there's no real value in breaking the existing convention.
>
> -Peff

Agreed - tests 110 and 111 in t1300-repo-config.sh fail. After that, "make test" gives up, losing about 14000 lines of output.

Sorry for the noise,
Cheers ... Duncan.
Junio C Hamano· Oct 21, 2016, 17:19 UTC · re: Jeff King · lore

Re: [BUG] [PATCH]: run-command.c

Jeff King <peff@peff.net> writes:
Show 7 quoted lines
>> 16:42:45$ cat /proc/2601/cmdline | xargs -0 -n1 echo
>> /bin/sh
>> -c
>> echo $PWD;sleep 600
>> echo $PWD;sleep 600
>
> This duplicated argument is expected and normal.
Well explained.  Thanks.

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