linux-kernel - RE: [PATCH 1/5] fs/ntfs3: Use kmalloc

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Date:   Thu, 2 Sep 2021 14:03:17 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Joe Perches' <joe@...ches.com>,
        Kari Argillander <kari.argillander@...il.com>,
        Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        "ntfs3@...ts.linux.dev" <ntfs3@...ts.linux.dev>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/5] fs/ntfs3: Use kmalloc_array over kmalloc with
 multiply

From: Joe Perches
> Sent: 01 September 2021 03:41
> 
> On Tue, 2021-08-31 at 21:15 +0300, Kari Argillander wrote:
> > If we do not use kmalloc_array we get checkpatch warning. It is also
> > little safer if something goes wrong with coding.
> []
> > diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c
> []
> > @@ -707,7 +707,7 @@ static struct NTFS_DE *hdr_find_e(const struct ntfs_index *indx,
> >  		u16 *ptr;
> >  		int new_slots = ALIGN(2 * nslots, 8);
> >
> >
> > -		ptr = kmalloc(sizeof(u16) * new_slots, GFP_NOFS);
> > +		ptr = kmalloc_array(new_slots, sizeof(u16), GFP_NOFS);
> >  		if (ptr)
> >  			memcpy(ptr, offs, sizeof(u16) * max_idx);
> 
> This multiplication could also overflow.

Not if kmalloc_array() has suceeded.
OTOH the ALIGN(2 * nslots, 8) can also go wrong.
(But probably not if the previous kmalloc() for 1/2 the size worked.)

But there really ought to be some kind of bound check earlier.

	David

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