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Subject[PATCH] Linux 2.6: shebang handling in fs/binfmt_script.c
Hi!

In a newsgroup about unix shells we had a discussion, why it is not
possible to pass more than one argument to an interpreter using the
shebang line of a script. We found, that this behaviour is rather
OS dependent. See Sven Mascheck's page for details:
http://www.in-ulm.de/~mascheck/various/shebang/

As I'm really missing this feature in Linux and changing this would not
break anything (unless someone uses rather unportable "#!cmd x y" to
pass _one_ argument "x y" containing spaces), I'd like to know if it's
possible to apply the patch below to the kernel.

It also allows to pass whitespace by using '\' as escape character:
"\t" => TAB
"\n" => LF
"\ " => SPC
"\\" => backslash
All other backslashes are discarded.

This allows something like
#!/usr/bin/awk -F \t -f

This part could break old scripts if the interpreter's path/filename or
the arguments contain backslashes. Although I don't consider this a real
problem, this feature can be deactivated by removing the
if (c=='\\') { ... }
part from the patch.
Another change: -ENOEXEC is returned, if the shebang line is too long.
So, excessive characters are not dropped silently any more.

The patch is tested for 2.6.1, but also applies cleanly to 2.6.2. I can
also send a tested patch for 2.4.24.

[ CC me on replies, please, as I'm not subscribed. ]

Kind regards
Hansjoerg Lipp

--- linux-2.6.1/fs/binfmt_script.c.orig 2004-02-06 22:21:30.000000000 +0100
+++ linux-2.6.1/fs/binfmt_script.c 2004-02-06 22:21:30.000000000 +0100
@@ -18,10 +18,16 @@

static int load_script(struct linux_binprm *bprm,struct pt_regs *regs)
{
- char *cp, *i_name, *i_arg;
+ char *cp;
struct file *file;
char interp[BINPRM_BUF_SIZE];
int retval;
+ char *argv[(BINPRM_BUF_SIZE-1)/2];
+ char **cur_arg;
+ unsigned argc;
+ int in_arg;
+ char *end, *dest;
+ char c;

if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') || (bprm->sh_bang))
return -ENOEXEC;
@@ -35,51 +41,47 @@
fput(bprm->file);
bprm->file = NULL;

- bprm->buf[BINPRM_BUF_SIZE - 1] = '\0';
- if ((cp = strchr(bprm->buf, '\n')) == NULL)
- cp = bprm->buf+BINPRM_BUF_SIZE-1;
- *cp = '\0';
- while (cp > bprm->buf) {
- cp--;
- if ((*cp == ' ') || (*cp == '\t'))
- *cp = '\0';
- else
- break;
+ in_arg=0;
+ cur_arg=argv;
+ argc=0;
+ dest=bprm->buf+2;
+ end=bprm->buf+BINPRM_BUF_SIZE;
+ for (cp=bprm->buf+2;cp<end;++cp) {
+ c=*cp;
+ if (c==' '|| c=='\t' || c=='\n' || !c) {
+ if (in_arg) {
+ in_arg=0;
+ *dest++=0;
+ }
+ if (c=='\n' || !c) break;
+ } else {
+ if (c=='\\') {
+ if (++cp>=end) return -ENOEXEC;
+ c=*cp;
+ if (c=='\n' || !c) return -ENOEXEC;
+ if (c=='t')
+ c='\t';
+ else if (c=='n')
+ c='\n';
+ }
+ if (!in_arg) {
+ in_arg=1;
+ argc++;
+ *cur_arg++=dest;
+ }
+ *dest++=c;
+ }
}
- for (cp = bprm->buf+2; (*cp == ' ') || (*cp == '\t'); cp++);
- if (*cp == '\0')
- return -ENOEXEC; /* No interpreter name found */
- i_name = cp;
- i_arg = 0;
- for ( ; *cp && (*cp != ' ') && (*cp != '\t'); cp++)
- /* nothing */ ;
- while ((*cp == ' ') || (*cp == '\t'))
- *cp++ = '\0';
- if (*cp)
- i_arg = cp;
- strcpy (interp, i_name);
- /*
- * OK, we've parsed out the interpreter name and
- * (optional) argument.
- * Splice in (1) the interpreter's name for argv[0]
- * (2) (optional) argument to interpreter
- * (3) filename of shell script (replace argv[0])
- *
- * This is done in reverse order, because of how the
- * user environment and arguments are stored.
- */
+ if (cp>=end||!argc) return -ENOEXEC;
+
+ strcpy (interp, argv[0]);
remove_arg_zero(bprm);
retval = copy_strings_kernel(1, &bprm->interp, bprm);
- if (retval < 0) return retval;
- bprm->argc++;
- if (i_arg) {
- retval = copy_strings_kernel(1, &i_arg, bprm);
- if (retval < 0) return retval;
- bprm->argc++;
- }
- retval = copy_strings_kernel(1, &i_name, bprm);
- if (retval) return retval;
+ if (retval < 0) return retval;
bprm->argc++;
+ retval = copy_strings_kernel(argc, argv, bprm);
+ if (retval < 0) return retval;
+ bprm->argc += argc;
bprm->interp = interp;

/*
-
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