lkml.org 
[lkml]   [2018]   [Apr]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: INFO: rcu detected stall in bitmap_parselist
From
Date
Yury Norov wrote:
> Hi Tetsuo,
>
> Thanks for the patch.
>
> On Wed, Apr 04, 2018 at 09:21:43PM +0900, Tetsuo Handa wrote:
> > Yury, are you OK with this patch?
> >
> >
> > >From 7f21827cdfe9780b4949b22bcd19efa721b463d2 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > Date: Wed, 4 Apr 2018 21:12:10 +0900
> > Subject: [PATCH] lib/bitmap: Rewrite __bitmap_parselist().
> >
> > syzbot is catching stalls at __bitmap_parselist() [1]. The trigger is
> >
> > unsigned long v = 0;
> > bitmap_parselist("7:,", &v, BITS_PER_LONG);
>
> Could you add this case to the test_bitmap_parselist()?
>
> > which results in hitting infinite loop at
> >
> > while (a <= b) {
> > off = min(b - a + 1, used_size);
> > bitmap_set(maskp, a, off);
> > a += group_size;
> > }
> >
> > due to used_size == group_size == 0.
> >
> > Current code is difficult to read due to too many flag variables.
> > Let's rewrite it.
>
> I also don't like current implementation of bitmap_parselist(), but
> discussion on new code may take some time. Can you submit minimal
> fix in separated patch to let people discuss your new implementation
> without rush?

OK. Then you can write the patch. You know current code better than I.

> > @@ -485,6 +485,58 @@ int bitmap_print_to_pagebuf(bool list, char *buf, const unsigned long *maskp,
> > }
> > EXPORT_SYMBOL(bitmap_print_to_pagebuf);
> >
> > +static bool get_uint(const char **buf, unsigned int *res)
> > +{
> > + const char *p = *buf;
> > +
> > + if (!isdigit(*p))
> > + return false;
> > + *res = simple_strtoul(p, (char **) buf, 10);
>
> In comment to simple_strtoul(): "This function is obsolete. Please
> use kstrtoul instead."

I intentionally choose simple_strtoul() because next delimiter (e.g. '-')
starts at returned address. kstrtoul() fails if next letter starts.

>
> > + return p < *buf;

I think I should limit to "0 <= *res <= INT_MAX" range in order to avoid
overflow at start += group_size.

> > +}
> > +
> > +static int __bitmap_parse_one_chunk(const char *buf, unsigned long *maskp,
> > + const unsigned int nmaskbits)
> > +{
> > + unsigned int start;
> > + unsigned int end;
> > + unsigned int group_size;
> > + unsigned int used_size;
> > +
> > + while (*buf && isspace(*buf))
> > + buf++;
> > + if (!get_uint(&buf, &start))
> > + return -EINVAL;
> > + if (*buf == '-') {
> > + buf++;
> > + if (!get_uint(&buf, &end) || start > end)
> > + return -EINVAL;
> > + if (*buf == ':') {
> > + buf++;
> > + if (!get_uint(&buf, &used_size) || *buf++ != '/' ||
> > + !get_uint(&buf, &group_size) ||
> > + used_size > group_size)
> > + return -EINVAL;
>
> So this is still not safe against "1-10:0/0", or I miss something?
> (This is another testcase we should add to test_bitmap.c)

Indeed. We need to make more testcases.

> > + while (buflen && !err) {
> > + char *cp;
> > + char tmpbuf[256];
> > + unsigned int size = min(buflen,
> > + (unsigned int) sizeof(tmpbuf) - 1);
> > +
> > + if (!is_user)
> > + memcpy(tmpbuf, buf, size);
> > + else if (copy_from_user(tmpbuf, (const char __user __force *)
> > + buf, size))
> > + return -EFAULT;
>
> This is not safe against this:
> "[250 whitespaces] 567-890:123/456"

Do we need to accept such insane entry?

>
> And it will be Schlemiel the painter's-styled algorithm for input like:
> "1,2,3,4, ... ,98,99,100".
>
> I think we need something like __bitmap_parse_get_chunk() to copy
> coma-separated substrings.

\
 
 \ /
  Last update: 2018-04-04 17:59    [W:0.042 / U:2.768 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site