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Re: [PATCH 2/2] run-command: Add interpreter permissions check

From
Junio C Hamano <gitster@pobox.com>
Date
Dec 6, 2011, 22:47 UTC
Message-ID
<7vk469e2rn.fsf@alter.siamese.dyndns.org>
In-Reply-To
<1323207503-26581-3-git-send-email-fransklaver@gmail.com>
Frans Klaver <fransklaver@gmail.com> writes:
Show 52 quoted lines
> If a script is started and the interpreter of that script given in the
> shebang cannot be started due to permissions, we can get a rather
> obscure situation. All permission checks pass for the script itself,
> but we still get EACCES from execvp.
>
> Try to find out if the above is the case and warn the user about it.
>
> Signed-off-by: Frans Klaver <fransklaver@gmail.com>
> ---
>  run-command.c          |   66 +++++++++++++++++++++++++++++++++++++++++++----
>  t/t0061-run-command.sh |   22 ++++++++++++++++
>  2 files changed, 82 insertions(+), 6 deletions(-)
>
> diff --git a/run-command.c b/run-command.c
> index 5e38c5a..b8cf8d4 100644
> --- a/run-command.c
> +++ b/run-command.c
> @@ -194,6 +194,63 @@ static int have_read_execute_permissions(const char *path)
>  	return 0;
>  }
>  
> +static void check_interpreter(const char *cmd)
> +{
> +	FILE *f;
> +	struct strbuf sb = STRBUF_INIT;
> +	/* bash reads an 80 character line when determining the interpreter.
> +	 * BSD apparently only allows 32 characters, as it is the size of
> +	 * your average binary executable header.
> +	 */
> +	char firstline[80];
> +	char *interpreter = NULL;
> +	size_t s, i;
> +
> +	f = fopen(cmd, "r");
> +	if (!f) {
> +		error("cannot open file '%s': %s\n", cmd, strerror(errno));
> +		return;
> +	}
> +
> +	s = fread(firstline, 1, sizeof(firstline), f);
> +	if (s < 2) {
> +		trace_printf("cannot determine file type");
> +		fclose(f);
> +		return;
> +	}
> +
> +	if (firstline[0] != '#' || firstline[1] != '!') {
> +		trace_printf("file '%s' is not a script or"
> +				" is a script without '#!'", cmd);
> +		fclose(f);
> +		return;
> +	}
Nice touches to silently pass scripts that do not begin with she-bang.
Show 8 quoted lines
> +
> +	/* see if the given path has the executable bit set */
> +	for (i = 2; i < s; i++) {
> +		if (!interpreter && firstline[i] != ' ' && firstline[i] != '\t')
> +			interpreter = firstline + i;
> +
> +		if (interpreter && (firstline[i] == ' ' ||
> +				firstline[i] == '\n')) {
Curious.
"#!<TAB>/bin/bash<TAB><LF>" would cause you to check "/bin/bash<TAB>"?
> +			strbuf_add(&sb, interpreter,
> +					(firstline + i) - interpreter);
> +			break;
> +		}
Wouldn't strcspn() work better instead of this loop?
Show 25 quoted lines
> +	}
> +	if (!sb.len) {
> +		error("could not determine interpreter");
> +		strbuf_release(&sb);
> +		return;
> +	}
> +
> +	if (!have_read_execute_permissions(sb.buf))
> +		error("bad interpreter: no read/execute permissions on '%s'\n",
> +				sb.buf);
> +
> +	strbuf_release(&sb);
> +}
> +
>  static void diagnose_execvp_eacces(const char *cmd, const char **argv)
>  {
>  	/* man 2 execve states that EACCES is returned for:
> @@ -209,8 +266,8 @@ static void diagnose_execvp_eacces(const char *cmd, const char **argv)
>  	char *next;
>  
>  	if (strchr(cmd, '/')) {
> -		if (!have_read_execute_permissions(cmd))
> -			error("no read/execute permissions on '%s'\n", cmd);
> +		if (have_read_execute_permissions(cmd))
> +			check_interpreter(cmd);
I would have expected the overall logic to be more like this:
	if we cannot read and execute it then
        	that in itself is an error (i.e. the error message from [1/2])
	else if we can read it then
		let's see if there is an error in the interpreter.

It is unnatural to see "if we can read and execute, then see if there is anything wrong with the interpreter" and _nothing else_ here. If you made the "have_read_execute_permissions()" to issue the error message you used to give in your [1/2] patch here, that is OK from the point of view of the overall code structure, but then the function is no longer "do we have permissions" boolean check and needs to be renamed. And if you didn't, then I have to wonder why we do not need the error message you added in your [1/2].

Show 50 quoted lines
> @@ -233,10 +290,7 @@ static void diagnose_execvp_eacces(const char *cmd, const char **argv)
>  				error("no read/execute permissions on '%s'\n",
>  						sb.buf);
>  			else
> -				warn("file '%s' exists and permissions "
> -				"seem OK.\nIf this is a script, see if you "
> -				"have sufficient privileges to run the "
> -				"interpreter", sb.buf);
> +				check_interpreter(sb.buf);
>  		}
>  
>  		strbuf_release(&sb);
> diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh
> index b39bd16..39bfaef 100755
> --- a/t/t0061-run-command.sh
> +++ b/t/t0061-run-command.sh
> @@ -13,6 +13,18 @@ cat >hello-script <<-EOF
>  EOF
>  >empty
>  
> +cat >someinterpreter <<-EOF
> +	#!$SHELL_PATH
> +	cat hello-script
> +EOF
> +>empty
> +
> +cat >incorrect-interpreter-script <<-EOF
> +	#!someinterpreter
> +	cat hello-script
> +EOF
> +>empty
> +
>  test_expect_success 'start_command reports ENOENT' '
>  	test-run-command start-command-ENOENT ./does-not-exist
>  '
> @@ -48,4 +60,14 @@ test_expect_success POSIXPERM 'run_command reports EACCES, search path permision
>  	grep "no read/execute permissions on" err
>  '
>  
> +test_expect_success POSIXPERM 'run_command reports EACCES, interpreter fails' '
> +	cat incorrect-interpreter-script >hello.sh &&
> +	chmod +x hello.sh &&
> +	chmod -x someinterpreter &&
> +	test_must_fail test-run-command run-command ./hello.sh 2>err &&
> +
> +	grep "fatal: cannot exec.*hello.sh" err &&
> +	grep "bad interpreter" err
> +'
> +
>  test_done
Previous: Frans KlaverNext: Frans Klaver
Message 18 of 25 in “run-command.c: Accept EACCES as command not found”
  1. run-command.c: Accept EACCES as command not foundFrans Klaver, Nov 21, 2011
  2. Junio C HamanoNov 21, 2011
  3. Frans KlaverNov 21, 2011
  4. Junio C HamanoNov 21, 2011
  5. Frans KlaverNov 22, 2011
  6. Frans KlaverNov 23, 2011
  7. Nguyen Thai Ngoc DuyNov 23, 2011
  8. Frans KlaverNov 23, 2011
  9. Frans KlaverNov 23, 2011
  10. 0/2 run-command: Add EACCES diagnosticsFrans Klaver, Dec 6, 2011
  11. 1/2 run-command: Add checks after execvp fails with EACCESFrans Klaver, Dec 6, 2011
  12. Junio C HamanoDec 6, 2011
  13. Frans KlaverDec 7, 2011
  14. Frans KlaverDec 8, 2011
  15. Junio C HamanoDec 9, 2011
  16. Frans KlaverDec 9, 2011
  17. 2/2 run-command: Add interpreter permissions checkFrans Klaver, Dec 6, 2011
  18. Junio C HamanoDec 6, 2011
  19. Frans KlaverDec 7, 2011
  20. 0/2 run-command: Add eacces diagnosticsFrans Klaver, Dec 13, 2011
  21. 1/2 run-command: Add checks after execvp fails with EACCESFrans Klaver, Dec 13, 2011
  22. Junio C HamanoDec 13, 2011
  23. Frans KlaverDec 14, 2011
  24. Frans KlaverDec 14, 2011
  25. 2/2 run-command: Add interpreter permissions checkFrans Klaver, Dec 13, 2011

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