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

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Message-ID: <20190927030237.GE22969@cs-dulles.cs.umn.edu>
Date:   Thu, 26 Sep 2019 22:02:37 -0500
From:   Navid Emamdoost <navid.emamdoost@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Al Viro <viro@...iv.linux.org.uk>, 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 Thu, Sep 26, 2019 at 10:00:31AM +0200, Jan Kara wrote:
> 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
Thanks for clarification.
> -- 
> Jan Kara <jack@...e.com>
> SUSE Labs, CR