linux-ext4 - Re: [patch]check NULL pointer

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Message-ID: <1308011473.15392.114.camel@sli10-conroe>
Date:	Tue, 14 Jun 2011 08:31:13 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	Ted Ts'o <tytso@....edu>
Subject: Re: [patch]check NULL pointer

On Mon, 2011-06-13 at 17:20 +0800, Lukas Czerner wrote:
> On Mon, 13 Jun 2011, Shaohua Li wrote:
> 
> > On Fri, 2011-06-10 at 16:32 +0800, Lukas Czerner wrote:
> > > On Fri, 10 Jun 2011, Shaohua Li wrote:
> > > 
> > > > On Thu, 2011-06-09 at 22:51 +0800, Eric Sandeen wrote:
> > > > > On 6/9/11 4:24 AM, Lukas Czerner wrote:
> > > > > > On Thu, 9 Jun 2011, Shaohua Li wrote:
> > > > > > 
> > > > > >> orig_data could be NULL.
> > > > > > 
> > > > > > Now, that is the commit description :). Could you please be more
> > > > > > descriptive in the "descritpion" ? Also the subject is not right either,
> > > > > > please see Documentation/SubmittingPatches
> > > > > 
> > > > > Yes; if possible please use the commit message to describe how/why orig_data
> > > > > can be NULL; a testcase if one exists; the resulting flaw (null pointer deref?)
> > > > > etc.
> > > > > 
> > > > > something like:
> > > > > 
> > > > > Subject: [PATCH] ext4: check for NULL orig_data pointer in mount paths
> > > > > 
> > > > > The orig_data pointer in ext4_fill_super()  and ext4_remount()
> > > > > can be null if < ??? >, which can lead to < ??? > in the mount
> > > > > and remount paths.  This can be demonstrated by < ??? >.  
> > > > > To avoid this, we can simply test for the null pointer
> > > > > and return an error in ext4_fill_super() and ext4_remount().
> > > > I thought the reason is pretty straightforward, anyway here is the
> > > > updated patch.
> > > > 
> > > > Subject: [patch]ext4: check NULL pointer for mount and remount
> > > > 
> > > > orig_data could be NULL, because the memory allocation of kstrdup() could fail.
> > > > Add the NULL check.
> > > 
> > > I am sorry, but as I pointed out in previous mail this is not true.
> > > *orig_data can be also NULL in the case that *data is NULL and hence
> > > there is no reason for exiting with error. Also please use the subject
> > > Eric suggested.
> > Hmm, maybe we just don't use the pointer if it's NULl. it's just print
> > info anyway.
> > 
> > Subject: [patch]ext4: check NULL orig_data pointer for mount and remount
> > 
> > orig_data could be NULL, because the memory allocation of kstrdup()
> > could fail or data is NULL. Add the NULL check.
> > 
> > Signed-off-by: Shaohua Li <shaohua.li@...el.com>
> > 
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index cc5c157..68eba3b 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -3706,7 +3706,7 @@ no_journal:
> >  
> >  	ext4_msg(sb, KERN_INFO, "mounted filesystem with%s. "
> >  		 "Opts: %s%s%s", descr, sbi->s_es->s_mount_opts,
> > -		 *sbi->s_es->s_mount_opts ? "; " : "", orig_data);
> > +		 *sbi->s_es->s_mount_opts ? "; " : "", orig_data ? : ";");
> 
> Hi,
> 
> so you are trying resolve the problem when the allocation fails right ?
> But what you do is not solving anything, but rather hiding it and it is
> not different than we had before.
> 
> So what about this:
> 
> if (data && !orig_data)
> 	return ret;
how could this work? if data is NULL, orig_data will be NULL, the
ext4_msg will still use a NULL pointer.

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