linux-kernel - Re: Uninline kcalloc

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Date:	Wed, 15 Feb 2012 22:10:59 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Pekka Enberg <penberg@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Jesper Juhl <jj@...osbits.net>, Jens Axboe <axboe@...nel.dk>,
	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>,
	David Rientjes <rientjes@...gle.com>
Subject: Re: Uninline kcalloc

On Feb 15, 2012, at 2:34 PM, Christoph Lameter wrote:
> Any allocation larger than MAX_ORDER << PAGE_SHIFT will fail since the
> page allocator cannot serve larger contigous pages.

Yes, any number larger than KMALLOC_MAX_SIZE would do the trick.
The question is whether people would like to adopt

kmalloc(ARRAY_BYTES(n, size), ...);

or

knalloc(n, size, ...);

Besides, I am worried that ARRAY_BYTES is error-prone because you
have to make sure that ARRAY_BYTES is used only in *alloc, not
elsewhere, not in forms like ARRAY_BYTES(n, size) + padding_size,
etc.  If ARRAY_BYTES is mostly used with kmalloc(), and the only
safe form is kmalloc(ARRAY_BYTES(n, size), ...), then adding a new
allocator knalloc(n, size, ...) seems like a simpler choice.

BTW, here goes a partial list of places where the new allocator
could be used to simplify existing checks.

fs/cifs/cifsacl.c:912

        if (num_aces > ULONG_MAX / sizeof(struct cifs_ace *))
                return;                 
        ppace = kmalloc(num_aces * sizeof(struct cifs_ace *),
                        GFP_KERNEL);

fs/cifs/asn1.c:428

        if (size < 2 || size > UINT_MAX/sizeof(unsigned long))
                return 0;

        *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);

fs/nfs/callback_xdr.c:308

        if (n > ULONG_MAX / sizeof(*args->devs)) {
                status = htonl(NFS4ERR_BADXDR);
                goto out;               
        }

        args->devs = kmalloc(n * sizeof(*args->devs), GFP_KERNEL);

net/ipv4/netfilter/nf_nat_snmp_basic.c:447

        if (size < 2 || size > ULONG_MAX/sizeof(unsigned long))
                return 0;               

        *oid = kmalloc(size * sizeof(unsigned long), GFP_ATOMIC);

drivers/staging/comedi/comedi_fops.c:673

        insns =
            kcalloc(insnlist.n_insns, sizeof(struct comedi_insn), GFP_KERNEL);

I believe there are more places without those checks, where the new
allocator can offer better security.

- xi

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