linux-kernel - Re: [PATCH] udf: prevent memory leak in udf_new

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Message-ID: <20190926080031.GB12013@quack2.suse.cz>
Date:   Thu, 26 Sep 2019 10:00:31 +0200
From:   Jan Kara <jack@...e.cz>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Navid Emamdoost <navid.emamdoost@...il.com>,
        Jan Kara <jack@...e.com>, emamd001@....edu, kjlu@....edu,
        smccaman@....edu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] udf: prevent memory leak in udf_new_inode

On Wed 25-09-19 23:24:08, Al Viro wrote:
> On Wed, Sep 25, 2019 at 04:39:03PM -0500, Navid Emamdoost wrote:
> > In udf_new_inode if either udf_new_block or insert_inode_locked fials
> > the allocated memory for iinfo->i_ext.i_data should be released.
> 
> "... because of such-and-such reasons" part appears to be missing.
> Why should it be released there?
> 
> > Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
> > ---
> >  fs/udf/ialloc.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
> > index 0adb40718a5d..b8ab3acab6b6 100644
> > --- a/fs/udf/ialloc.c
> > +++ b/fs/udf/ialloc.c
> > @@ -86,6 +86,7 @@ struct inode *udf_new_inode(struct inode *dir, umode_t mode)
> >  			      dinfo->i_location.partitionReferenceNum,
> >  			      start, &err);
> >  	if (err) {
> > +		kfree(iinfo->i_ext.i_data);
> >  		iput(inode);
> >  		return ERR_PTR(err);
> >  	}
> 
> Have you tested that?  Because it has all earmarks of double-free;
> normal eviction pathway ought to free the damn thing.  <greps around
> a bit>
> 
> Mind explaining what's to stop ->evict_inode (== udf_evict_inode) from
> hitting
>         kfree(iinfo->i_ext.i_data);
> considering that this call of kfree() appears to be unconditional there?

Exactly. udf_evict_inode() is responsible for freeing iinfo->i_ext.i_data
so the patch would result in double free.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR