[patch] module: static checker complains about negative values

[patch] module: static checker complains about negative values

[Dan Carpenter]

We cap "stat.size" at INT_MAX but we don't check for negative values so
my static checker complains.  At this point, you already have control of
the kernel and if you start passing negative values here then you
deserve what happens next.

On 64 bit systems the vmalloc() will definitely fail.  On 32 bit systems
we truncate the upper 32 bits away so that could succeed.  I haven't
followed it further than that.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/kernel/module.c b/kernel/module.c
index 626d164..26e0d15 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -2536,7 +2536,7 @@ static int copy_module_from_fd(int fd, struct load_info *info)
 	}
 
 	/* Don't hand 0 to vmalloc, it whines. */
-	if (stat.size == 0) {
+	if (stat.size <= 0) {
 		err = -EINVAL;
 		goto out;
 	}

Re: [patch] module: static checker complains about negative values

[Rusty Russell]

Dan Carpenter <dan.carpenter@oracle.com> writes:

> We cap "stat.size" at INT_MAX but we don't check for negative values so
> my static checker complains.  At this point, you already have control of
> the kernel and if you start passing negative values here then you
> deserve what happens next.
>
> On 64 bit systems the vmalloc() will definitely fail.  On 32 bit systems
> we truncate the upper 32 bits away so that could succeed.  I haven't
> followed it further than that.
>
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

If vfs_getattr() returns a negative stat.size, we have worse problems.

I'd rather see you sprinkle assertions like that into the code, so we
can make sure that can't happen for any fs's getattr().

Cheers,
Rusty.

Re: [patch] module: static checker complains about negative values

[Dan Carpenter]

On Tue, May 20, 2014 at 11:16:04AM +0930, Rusty Russell wrote:
> Dan Carpenter <dan.carpenter@oracle.com> writes:
> 
> > We cap "stat.size" at INT_MAX but we don't check for negative values so
> > my static checker complains.  At this point, you already have control of
> > the kernel and if you start passing negative values here then you
> > deserve what happens next.
> >
> > On 64 bit systems the vmalloc() will definitely fail.  On 32 bit systems
> > we truncate the upper 32 bits away so that could succeed.  I haven't
> > followed it further than that.
> >
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> 
> If vfs_getattr() returns a negative stat.size, we have worse problems.
> 
> I'd rather see you sprinkle assertions like that into the code, so we
> can make sure that can't happen for any fs's getattr().

Yeah.  I was lazy.  Sorry.  I can just hand edit my database to say that
i_size_read() returns a reasonable number...

regards,
dan carpenter