linux-kernel - Re: [PATCH v2] fs: fs_parser: avoid NULL param->string to kstrtouint

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Message-ID: <20190816024654.GA12185@sol.localdomain>
Date:   Thu, 15 Aug 2019 19:46:54 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     viro@...iv.linux.org.uk
Cc:     dhowells@...hat.com, gregkh@...uxfoundation.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, miklos@...redi.hu,
        tglx@...utronix.de, Yin Fengwei <nh26223.lmm@...il.com>,
        kstewart@...uxfoundation.org
Subject: Re: [PATCH v2] fs: fs_parser: avoid NULL param->string to kstrtouint

On Sat, Jul 20, 2019 at 07:29:49AM +0800, Yin Fengwei 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>
> ---
> ChangeLog:
>  v1 -> v2:
>    - Fix typo in v1
>    - Remove braces {} from single statement blocks
> 
>  fs/fs_parser.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/fs_parser.c b/fs/fs_parser.c
> index 83b66c9e9a24..7498a44f18c0 100644
> --- a/fs/fs_parser.c
> +++ b/fs/fs_parser.c
> @@ -206,6 +206,9 @@ int fs_parse(struct fs_context *fc,
>  	case fs_param_is_fd: {
>  		switch (param->type) {
>  		case fs_value_is_string:
> +			if (!result->has_value)
> +				goto bad_value;
> +
>  			ret = kstrtouint(param->string, 0, &result->uint_32);
>  			break;
>  		case fs_value_is_file:
> -- 
> 2.17.1

Reviewed-by: Eric Biggers <ebiggers@...nel.org>

Al, can you please apply this patch?

- Eric