linux-kernel - Re: [PATCH] fs: fs_parser: avoid NULL param->string to kstrtouint

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Date:   Sat, 20 Jul 2019 07:28:19 +0800
From:   YinFengwei <nh26223.lmm@...il.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Yin Fengwei <nh26223.lmm@...il.com>,
        David Howells <dhowells@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kate Stewart <kstewart@...uxfoundation.org>
Subject: Re: [PATCH] fs: fs_parser: avoid NULL param->string to kstrtouint

On Fri, Jul 19, 2019 at 03:37:37PM +0200, Dmitry Vyukov wrote:
> On Fri, Jul 19, 2019 at 2:44 PM Yin Fengwei <nh26223.lmm@...il.com> wrote:
> >
> > syzbot reported general protection fault in kstrtouint:
> > https://lkml.org/lkml/2019/7/18/328
> >
> > From the log, if the mount option is something like:
> >    fd,XXXXXXXXXXXXXXXXXXXX
> >
> > The default parameter (which has NULL param->string) will be
> > passed to vfs_parse_fs_param. Finally, this NULL param->string
> > is passed to kstrtouint and trigger NULL pointer access.
> >
> > Reported-by: syzbot+398343b7c1b1b989228d@...kaller.appspotmail.com
> > Fixes: 71cbb7570a9a ("vfs: Move the subtype parameter into fuse")
> >
> > Signed-off-by: Yin Fengwei <nh26223.lmm@...il.com>
> > ---
> >  fs/fs_parser.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/fs/fs_parser.c b/fs/fs_parser.c
> > index d13fe7d797c2..578e6880ac67 100644
> > --- a/fs/fs_parser.c
> > +++ b/fs/fs_parser.c
> > @@ -210,6 +210,10 @@ int fs_parse(struct fs_context *fc,
> >         case fs_param_is_fd: {
> >                 switch (param->type) {
> >                 case fs_value_is_string:
> > +                       if (result->has_value) {
> 
> !result->has_value ?
Yes. Should have ! in condition for NULL param->string. Will fix in v2.

Regards
Yin, Fengwei

> 
> > +                               goto bad_value;
> > +                       }
> > +
> >                         ret = kstrtouint(param->string, 0, &result->uint_32);
> >                         break;
> >                 case fs_value_is_file:
> > --
> > 2.17.1
> >
> > --
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