Re: [patch] cifs: integer overflow in parse_dacl()

[Dan Carpenter <dan.carpenter@oracle.com>]

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On Wed, Jan 11, 2012 at 07:20:29AM -0500, Jeff Layton wrote:
> On Wed, 11 Jan 2012 10:46:27 +0300
> Dan Carpenter <dan.carpenter@oracle.com> wrote:
> 
> > On 32 bit systems num_aces * sizeof(struct cifs_ace *) could overflow
> > leading to a smaller ppace buffer than we expected.
> > 
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > 
> > diff --git a/fs/cifs/cifsacl.c b/fs/cifs/cifsacl.c
> > index 72ddf23..c1b2544 100644
> > --- a/fs/cifs/cifsacl.c
> > +++ b/fs/cifs/cifsacl.c
> > @@ -909,6 +909,8 @@ static void parse_dacl(struct cifs_acl *pdacl, char *end_of_acl,
> >  		umode_t group_mask = S_IRWXG;
> >  		umode_t other_mask = S_IRWXU | S_IRWXG | S_IRWXO;
> >  
> > +		if (num_aces > ULONG_MAX / sizeof(struct cifs_ace *))
> > +			return;
> >  		ppace = kmalloc(num_aces * sizeof(struct cifs_ace *),
> >  				GFP_KERNEL);
> >  		if (!ppace) {
> 
> 
> Looks plausible. This function could use some work. I'm not sure why
> num_aces is signed here too...
> 
> The first arg to kmalloc is a size_t. Does that boil down to an unsigned
> long on all arches?

People have been submitting a lot of patches recently based on that
assumption.  It matches the check in kcalloc() as well.  According
to include/asm-generic/posix_types.h:

/*
 * Most 32 bit architectures use "unsigned int" size_t,
 * and all 64 bit architectures use "unsigned long" size_t.
 */

It would be better to user a lower limit, but I don't know the code
well enough to say if which one is good that won't break things...
A high number can trigger a kmalloc() failure and that puts annoying
spam in the dmesg.

regards,
dan carpenter

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