On Fri, Mar 27, 2020 at 09:51:34AM +0900, Tetsuo Handa wrote:
> diff --git a/fs/exec.c b/fs/exec.c
> index db17be51b112..ded3fa368dc7 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1761,11 +1761,17 @@ static int __do_execve_file(int fd, struct filename *filename,
> check_unsafe_exec(bprm);
> current->in_execve = 1;
>
> - if (!file)
> + if (!file) {
> file = do_open_execat(fd, filename, flags);
> - retval = PTR_ERR(file);
> - if (IS_ERR(file))
> - goto out_unmark;
> + retval = PTR_ERR(file);
> + if (IS_ERR(file))
> + goto out_unmark;
> + } else {
> + retval = deny_write_access(file);
> + if (retval)
> + goto out_unmark;
> + get_file(file);
> + }
I still don't like it. The bug is real, but... *yeccchhhh*
First of all, this assignment to "file" is misguiding -
assignment to bprm->file would've been a lot easier to
follow. Furthermore, the damn thing already has much
too confusing cleanup logics.
Why is
out:
if (bprm->mm) {
acct_arg_size(bprm, 0);
mmput(bprm->mm);
}
done on failure exit in this function and not in free_bprm(),
while dropping bprm->file is in free_bprm()?
Note that flush_old_exec() will zero bprm->mm (after it transfers
the damn thing into current->mm), so we are fine here. And getting
rid of that thing in __do_execve_file() simplifies the logics
in there, especially if you take everything from this
if (!file)
up to
retval = exec_binprm(bprm);
into a new function. All those goto out_unmark/goto out turn
into plain returns. And in __do_execve_file() we are left with
....
current->in_execve = 1;
retval = this_new_helper(whatever it needs passed to it);
current->fs->in_exec = 0;
current->in_execve = 0;
if (!retval) {
/* execve succeeded */
rseq_execve(current);
acct_update_integrals(current);
task_numa_free(current, false);
}
out_free:
free_bprm(bprm);
kfree(pathbuf);
out_files:
if (displaced)
put_files_struct(displaced);
out_ret:
if (filename)
putname(filename);
return retval;
which is a lot easier to follow. Especially if we lift the logics
for freeing pathbuf into free_bprm() as well (will need a flag there,
for "does ->filename need to be freed?"). And I really wonder if
sched_exec() is called in the right place - what's special about the
point after opening the binary to be and setting bprm->file to what
we got?
