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

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Message-ID: <CACT4Y+aVS5nn0Pv31tAOujcAPvCAOuK_iPZ1CCNbgAOL=JDvvg@mail.gmail.com>
Date:   Fri, 19 Jul 2019 15:37:37 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Yin Fengwei <nh26223.lmm@...il.com>
Cc:     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 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 ?

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