Re: Linux Kernel sctp_setsockopt() Integer Overflow

["Evgeny Demidov" <demidov () gleg net>]

Hello,

> On Sat, 15 May 2004 23:07:00 +0200 (CEST)
> Jirka Kosina <jikos () jikos cz> wrote:
> On Sat, 15 May 2004, Michael Tokarev wrote:
>
> > But kmalloc(0) will return NULL, and the whole 
> > setsockopt
> > will finish with errno set to ENOMEM.
> >
> > From 2.4 mm/slab.c:
> > void * kmalloc (size_t size, int flags)
> > {
> >         cache_sizes_t *csizep = cache_sizes;
> >
> >         for (; csizep->cs_size; csizep++) {
> >                 if (size > csizep->cs_size)
> >                         continue;
> >                 return __kmem_cache_alloc(flags & 
> > GFP_DMA ?
> >                          csizep->cs_dmacachep : 
> > csizep->cs_cachep, flags);
> >         }
> >         return NULL;
> > }
>
> How did you come from the above snippet of the code to 
> the idea that
> kmalloc(0) returns NULL?
>
> It allocates the number of bytes equal to the closest 
> larger value of
> cache_sizes->cs_size entries ... so on typical system 
> this would be 
> something like 32 or 64 bytes, depending on the page size 
> (see 
> include/linux/kmalloc_sizes.h) ... and of course returns 
> pointer to this 
> data, which is definitely not NULL.

Nice advisory, there are couple of bugs like this one ;-), 
but I always thought that negative 'optlen' values are 
filtered out in sys_setsockopt (net/socket.c):

<snip>
asmlinkage long sys_setsockopt(int fd, int level, int 
optname, char *optval, int optlen)
{
        int err;
        struct socket *sock;

[!]     if (optlen < 0)
                return -EINVAL;

        if ((sock = sockfd_lookup(fd, &err))!=NULL)
        {
                if (level == SOL_SOCKET)
                        err=sock_setsockopt(sock,level,optname,optval,optlen);
                else
                        err=sock->ops->setsockopt(sock, 
level, optname, optval, optlen);
                sockfd_put(sock);
        }
        return err;
}

</snip>

Best regards
-Evgeny Demidov

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