Re: fix must_not_trace_exec() test

Andy Lutomirski
2004-04-12T14:18:23Z

Olaf Dietsche wrote:

> Andrew Morton <akpm@osdl.org> writes:
>
>
> Although, I'd rather not lump together unrelated tests without
> renaming must_not_trace_exec(). Btw, can someone enlighten me what
> this atomic_read() test is all about.

Oops... your fix is obviously correct.

I assumed that the test was to check if the caller is a thread, but that sounds
odd -- wouldn't it stop being a thread after the exec anyway? Maybe that part
happens after compute_creds, so this prevents a race? Although I don't see how
it could be triggered if the thread never entered usermode before getting a new
fs/files/sighand.

Anyone?

>
> Regards, Olaf.
>
> diff -urN a/security/commoncap.c b/security/commoncap.c
> --- a/security/commoncap.c Mon Apr 12 10:38:17 2004
> +++ b/security/commoncap.c Mon Apr 12 11:10:38 2004
> @@ -118,9 +118,9 @@
> static inline int must_not_trace_exec (struct task_struct *p)
> {
> return ((p->ptrace & PT_PTRACED) && !(p->ptrace & PT_PTRACE_CAP))
> - || atomic_read(&current->fs->count) > 1
> - || atomic_read(&current->files->count) > 1
> - || atomic_read(&current->sighand->count) > 1;
> + || atomic_read(&p->fs->count) > 1
> + || atomic_read(&p->files->count) > 1
> + || atomic_read(&p->sighand->count) > 1;
> }
> [...]

--Andy