On Tue, Apr 21, 2020 at 08:16:15PM +0100, Al Viro wrote:
> On Tue, Apr 21, 2020 at 07:15:39PM +0200, Christoph Hellwig wrote:
> > Instead of having all the sysctl handlers deal with user pointers, which
> > is rather hairy in terms of the BPF interaction, copy the input to and
> > from userspace in common code. This also means that the strings are
> > always NUL-terminated by the common code, making the API a little bit
> > safer.
> >
> > As most handler just pass through the data to one of the common handlers
> > a lot of the changes are mechnical.
>
> > @@ -564,27 +564,38 @@ static ssize_t proc_sys_call_handler(struct file *filp, void __user *buf,
> > if (!table->proc_handler)
> > goto out;
> >
> > - error = BPF_CGROUP_RUN_PROG_SYSCTL(head, table, write, buf, &count,
> > - ppos, &new_buf);
> > + if (write) {
> > + kbuf = memdup_user_nul(ubuf, count);
> > + if (IS_ERR(kbuf)) {
> > + error = PTR_ERR(kbuf);
> > + goto out;
> > + }
> > + } else {
> > + error = -ENOMEM;
> > + kbuf = kzalloc(count, GFP_KERNEL);
>
> Better allocate count + 1 bytes here, that way a lot of insanity in the
> instances can be simply converted to snprintf(). Yes, I know it'll bring
> the Church Of Avoiding The Abomination Of Sprintf out of the woodwork,
> but...
FWIW, consider e.g. net/sunrpc/sysctl.c:
Nevermind that the read side should be simply
int err = proc_douintvec(table, write, buffer, lenp, ppos);
/* Display the RPC tasks on writing to rpc_debug */
if (!err && strcmp(table->procname, "rpc_debug") == 0)
rpc_show_tasks(&init_net);
return err;
the write side would become
len = snprintf(buffer, *lenp + 1, "0x%04x\n",
*(unsigned int *)table->data);
if (len > *lenp)
len = *lenp;
*lenp -= len;
*ppos += len;
return 0;
and I really wonder if lifting the trailing boilerplate into the caller would've
been better. Note that e.g. gems like
if (!first)
err = proc_put_char(&buffer, &left, '\t');
if (err)
break;
err = proc_put_long(&buffer, &left, lval, neg);
if (err)
break;
are due to lack of snprintf-to-user; now, lose the "to user" part and we suddenly
can be rid of that stuff...
