linux-kernel - Re: [Linux-kernel-mentees] [PATCH] hfs, hfsplus: Fix NULL pointer dereference in hfs_find

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Date:   Wed, 12 Aug 2020 03:13:06 -0400
From:   Peilin Ye <yepeilin.cs@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-fsdevel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzkaller-bugs@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [Linux-kernel-mentees] [PATCH] hfs, hfsplus: Fix NULL pointer
 dereference in hfs_find_init()

On Wed, Aug 12, 2020 at 09:08:27AM +0200, Greg Kroah-Hartman wrote:
> On Wed, Aug 12, 2020 at 02:55:56AM -0400, Peilin Ye wrote:
> > Prevent hfs_find_init() from dereferencing `tree` as NULL.
> > 
> > Reported-and-tested-by: syzbot+7ca256d0da4af073b2e2@...kaller.appspotmail.com
> > Signed-off-by: Peilin Ye <yepeilin.cs@...il.com>
> > ---
> >  fs/hfs/bfind.c     | 3 +++
> >  fs/hfsplus/bfind.c | 3 +++
> >  2 files changed, 6 insertions(+)
> > 
> > diff --git a/fs/hfs/bfind.c b/fs/hfs/bfind.c
> > index 4af318fbda77..880b7ea2c0fc 100644
> > --- a/fs/hfs/bfind.c
> > +++ b/fs/hfs/bfind.c
> > @@ -16,6 +16,9 @@ int hfs_find_init(struct hfs_btree *tree, struct hfs_find_data *fd)
> >  {
> >  	void *ptr;
> >  
> > +	if (!tree)
> > +		return -EINVAL;
> > +
> >  	fd->tree = tree;
> >  	fd->bnode = NULL;
> >  	ptr = kmalloc(tree->max_key_len * 2 + 4, GFP_KERNEL);
> > diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c
> > index ca2ba8c9f82e..85bef3e44d7a 100644
> > --- a/fs/hfsplus/bfind.c
> > +++ b/fs/hfsplus/bfind.c
> > @@ -16,6 +16,9 @@ int hfs_find_init(struct hfs_btree *tree, struct hfs_find_data *fd)
> >  {
> >  	void *ptr;
> >  
> > +	if (!tree)
> > +		return -EINVAL;
> > +
> 
> How can tree ever be NULL in these calls?  Shouldn't that be fixed as
> the root problem here?

I see, I will try to figure out what is going on with the reproducer.

Thank you,
Peilin Ye