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@xxxxxxxxxx> 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@xxxxxxxxxx>
> >
> > 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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