On Sat, Jun 06, 2009 at 08:22:44AM +0100, Al Viro wrote:
> On Thu, Jun 04, 2009 at 03:04:22AM +0400, Alexey Dobriyan wrote:
> > diff --git a/fs/binfmt_som.c b/fs/binfmt_som.c
> > index eff74b9..6c56262 100644
> > --- a/fs/binfmt_som.c
> > +++ b/fs/binfmt_som.c
> > @@ -174,6 +174,7 @@ static int map_som_binary(struct file *file,
> > up_write(¤t->mm->mmap_sem);
> > if (retval > 0 || retval < -1024)
> > retval = 0;
> > + set_task_exec_path(current, &bprm->file->f_path);
>
> Oh? Even on failure exits?
OK.
> > + if (!path->mnt || !path->dentry)
> > + return -ENOENT;
>
> Umm... I really don't like that. Note that path with NULL vfsmount
> and non-NULL dentry should never happen. If anything, we ought
> to add path_empty(path) (!(path)->mnt) and convert such places to it.
Why mntget/mntput handle NULL vfsmount?
> > +static inline void set_task_exec_path(struct task_struct *tsk, struct path *path)
> > +{
> > + struct path old_path;
> > +
> > + path_get(path);
> > + task_lock(tsk);
> > + old_path = tsk->exec_path;
> > + tsk->exec_path = *path;
> > + task_unlock(tsk);
> > + path_put(&old_path);
> > +}
>
> Do we ever have a right to do that to anything other than current? Note
> that fork() is a special case anyway...
Locking wise? Yes, why not.
> > + set_task_exec_path(tsk, &(struct path){ .mnt = NULL, .dentry = NULL });
>
> Ew...
:^)
> > + get_task_exec_path(current, &p->exec_path);
> > +
>
> We already have that value sitting there, so why not get_path(&p->exec_path)?
>
> The real problem I have with that we *really* can't umount the filesystem
> that used to host the binary anymore. At all.
OTOH, you can always answer the question what is executing unless task is
sufficiently dead.
Now, I dont' think anyone unmaps old executable except malicious stuff.
> Frankly, I'm almost tempted to add explicit way to switch the damn thing
> via /proc/self/something - e.g. allow a binary to write a pathname to
> /proc/self/set_exec and have that switch the sucker. The interesting
> part, of course, is figuring out the security implications of that...
I think nobody will use it.
I think /proc/*/exe should stay informational without task being able
to mangle it at will.
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