execl() fails with EACCES after setuid() call

Hello there,

my name is Matteo and I'm writing from Italy.

Maybe this is a very trivial issue but I'm going crazy on it.

I have a simple application, say test, owned by myuid.mygid, of course different from root, where myuid=31 mygid=31.

Inside it I just do:

...

res = setgid(31);
if (res != 0)
printf("setgid() failed\n");

res = setuid(31);
if (res != 0)
printf("setuid() failed\n");

res = execl("/usr/sbin/myapp", (char*) NULL);
printf("execl() returned %d\n", res);
if (res != 0)
printf("execl() error: %s (%d)\n", strerror(errno), errno);

...

Please note that myapp is owned by 0.mygid and is readable/executable by mygid and the same for /usr and /usr/sbin.

But execl() fails with EACCES.

It seems that setuid() is the real cause, because if I comment only it the result is OK.

Can anyone please tell me what's wrong?

Many many thanks,

Matteo.

This is strange. It should work.

I know you've already covered this, but as a sanity check, could you please copy and paste into a response on this site what you get as output to the following commands?

ls -lnad /usr/sbin
ls -ln   /usr/sbin/myapp

Hi,

first please excuse me for the duplicate post, of course it was not my intention but I couldn't remove the second one.

Then, doing a ls -lnad /usr/sbin I get

drwxr-x--- 2 0 31 4096 May 17 2007 /usr/sbin

and that should be OK, while ls -ln /usr/sbin/myapp gives

-rwxr-x--- 1 0 31 231477 May 17 2007 /usr/sbin/myapp

and that should be OK, too.

I can't really understand.

Thanks in advance,

Matteo.

I'm thinking of various ways to explore this. But while I'm thinking, there's another piece of the puzzle that I need, please.

What user are you logged in as when you run test? User 31? User 0 (root)? Someone else? And what is the primary group number for that user?

By the way, "test" would be a bad name for this, because that word is used elsewhere in the shell and as a standard runnable program.

(Sorry for the slow response. I'm kinda overwhelmed with things to do at this end.)