Re: [bug report] ceph: decode interval_sets for delegated inos

[Alex Elder <elder@riscstar.com>]

On 12/3/24 2:19 AM, Dan Carpenter wrote:
> Hello Jeff Layton,
> 
> Commit d48464878708 ("ceph: decode interval_sets for delegated inos")
> from Nov 15, 2019 (linux-next), leads to the following Smatch static
> checker warning:
> 
> 	fs/ceph/mds_client.c:644 ceph_parse_deleg_inos()
> 	warn: potential user controlled sizeof overflow 'sets * 2 * 8' '0-u32max * 8'
> 
> fs/ceph/mds_client.c
>      637 static int ceph_parse_deleg_inos(void **p, void *end,
>      638                                  struct ceph_mds_session *s)
>      639 {
>      640         u32 sets;
>      641
>      642         ceph_decode_32_safe(p, end, sets, bad);
>                                              ^^^^
> set to user data here.
> 
>      643         if (sets)
> --> 644                 ceph_decode_skip_n(p, end, sets * 2 * sizeof(__le64), bad);
>                                                     ^^^^^^^^^^^^^^^^^^^^^^^^^
> This is safe on 64bit but on 32bit systems it can integer overflow/wrap.

So the point of this is that "sets" is u32, and because that is
multiplied by 16 when passed to ceph_decode_skip_n(), the result
could exceed 32 bits?  I.e., would this address it?

	if (sets) {
	    size_t scale = 2 * sizeof(__le64);

	    if (sets < SIZE_MAX / scale)
		ceph_decode_skip_n(p, end, sets * scale, bad);
	    else
		goto bad;
	}

					-Alex


>      645         return 0;
>      646 bad:
>      647         return -EIO;
>      648 }
>      649
>      650 u64 ceph_get_deleg_ino(struct ceph_mds_session *s)
>      651 {
>      652         return 0;
>      653 }
>      654
> 
> regards,
> dan carpenter
>