[bug report] block: integer overflow in __bvec_gap_to_prev()

[Roman Smirnov]

Hello.

There is a case of integer overflow in __bvec_gap_to_prev():

	((bprv->bv_offset + bprv->bv_len) & lim->virt_boundary_mask);

bio_vec can cross multiple pages:

https://lore.kernel.org/lkml/20190215111324.30129-1-ming.lei@xxxxxxxxxx/t/

So, in case bio has one bio_vec bv_len can have a maximum value of UINT_MAX.
The check happens in bio_full(). In the case when bv_len is equal to
UINT_MAX and bv_offset is greater than zero, an overflow may occur.

Found by Linux Verification Center (linuxtesting.org) with Svace.