[SOLVED] Cannot open ./setuid_06

stf92 · 06-01-2013, 10:48 PM

Hi:

Code:

root@local:/home/semoi/z80_2013/emulate_uart# ls -l setuid_06
-rwsr-sr-x 1 root root 9181 2013-06-01 22:51 setuid_06*
root@local:/home/semoi/z80_2013/emulate_uart# file ./setuid_06
./setuid_06: setuid setgid ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), not stripped
root@local:/home/semoi/z80_2013/emulate_uart# whoami
root
root@local:/home/semoi/z80_2013/emulate_uart# ./setuid_06
Cannot open ./setuid_06
root@local:/home/semoi/z80_2013/emulate_uart#

I cannot understand why the system refuses to run this program. It did until yesterday. No longer now and I am using a security copy of the program. Besides, who is saying 'Cannot open ./setuid_06'? What can the system possible find wrong with the program?

NOTE: why I had to set the "set user or group ID on execution" bit I do not remember.

elvis4526 · 06-01-2013, 11:47 PM

1) What is this program exactly?
2) Are you on Slackware 64 bits ?

stf92 · 06-01-2013, 11:58 PM

Quote:

Originally Posted by elvis4526

1) What is this program exactly?
2) Are you on Slackware 64 bits ?

It outputs data through the machine's parallel port. Yes, this is Slackware 14.0 x86_64.

elvis4526 · 06-02-2013, 12:45 AM

Okay.
Since it's a 32 bits binary, did you install all the multilib packages provided by AlienBob ?

stf92 · 06-02-2013, 01:00 AM

No, I didn't. But I forgot something. I have the program source file. Now I'm trying to compile it in this, which is a 64-bit machine. Unfortunately, I get:

Code:

semoi@server:~/z80_p4/juan$ gcc -O2 -o p1 p1.c
p1.c:26:42: fatal error: asm/io.h: No such file or directory
compilation terminated.

The source has this line:

Code:

   #include <asm/io.h>        // for outb

locate asm/io.h finds hundreds of instances. I do not understand. In what directory should asm/io.h should be?

elvis4526 · 06-02-2013, 01:29 AM

Well yeah, if you try to run a 32 bits binary on a 64 bits system without any kind of multilib packages installed, this won't work for sure.
I don't think compiling it by hand without any kind of makefile or even some instructions from the maintainer of this program is a good idea.

I would suggest to install the multilib packages provided by alienBOB and then try again to launch the compiled binary to see how it goes.

wildwizard · 06-02-2013, 01:56 AM

Quote:

Originally Posted by stf92

The source has this line:

Code:

   #include <asm/io.h>        // for outb

locate asm/io.h finds hundreds of instances. I do not understand. In what directory should asm/io.h should be?

man outb gives <sys/io.h>

The code is old and needs to be updated for current kernel header layouts.

stf92 · 06-02-2013, 02:07 AM

But it is I who wrote the program and I have run it without problems many times already. Forget about the compilation on the 64-bit machine (gcc will produce 64 bit code). I was wrong. Do as if I were running a 32-bit machine. The program must do I/O. So it must do a setuid. For that, the owner must be root, otherwise the system won't let the program to do the setuid. As I learned in the internet, I must set the "set user or group ID on execution" bit of the file. So the file is left with these permissions:

-rwsr-sr-x

I always did this and the things went well. Now, when trying to run it, I get the 'Cannot open <file name>' message. If I remove the "s" bit, however, I can run it. But then the system does not let the program do the setuid. I must have touched something in the system. I have to recollect. Or perhaps I'm obviating some step now. But the source is exactly the same as when everything went well.

stf92 · 06-02-2013, 02:13 AM

Quote:

Originally Posted by wildwizard

man outb gives <sys/io.h>

The code is old and needs to be updated for current kernel header layouts.

Thank you very much. I was making a mistake. The program must be compiled in the 32-bit machine where it is to be run. That is, ggc must compile for 32 bits. To make it easy, I compile in the 32-bit machine remotely from a 64-bit machine (more comfortable place to work in). So no problems with the compilation now.

What I can't do is make run. I explained these things in the post above this. Again thanks, wildwizard.

NOTE: simply stated: with this permissions mask,

-rwsr-sr-x 1 semoi semoi 9181 2006-03-13 05:58 setuid_06

running the program the system will say 'Cannot open setuid_06'. With this one, the system will run it:

-rwxr-xr-x 1 semoi semoi 9181 2006-03-13 05:58 setuid_06

but then the program won't be able to operate correctly. The precise implications of using the "s" bit I do not know them.

stf92 · 06-02-2013, 04:20 AM

The fault was the user's and not the program's. This is a part of the source:

Code:

int main(int argc, char** argv){
        int     i;
        
        if (permisos()) {
                printf("Error getting permissions.\n");
                return 0;
        }
        
        infile = fopen(argv[1], "rb");
        if(!infile){
                fprintf(stderr, "Cannot open %s\n", argv[0]);
                return 0;
        }
        
        // fileno gets the file descriptor out of stream infile
        fstat(fileno(infile), &buf);
        filesize= buf.st_size - 10;     // get the file size
        printf("File size is %d decimal.\n", filesize);

        image= msk_data | msk_clock;
        outb(image, port);
        printf("Press a key to begin transmition."); getchar();

After trying to open the file

Code:

        infile = fopen(argv[1], "rb");
        if(!infile){
                fprintf(stderr, "Cannot open %s\n", argv[0]);
                return 0;
        }

the program checks for errors. In case it finds one, it prints the infamous message "Cannot open <argv[0]>". Here, a second error, because it should be argv[1], the filename that the user must type after the program name. I systematically forgot to specify a filename in the command line. Because I mistakenly wrote argv[0], the resulting message was 'Cannot open ./setuid_06', the name of the program. However the program should warn there is no argument. I had quite forgotten how to use it. That was my great question. Generally system and utilities messages are preceded by the name of the one who talks. This was preceded by nothing! For the record, I made this circumstance explicit in the thread.