mm/gup: do not return 0 from pin_user_pages_fast() for bad args These routines are not intended to return zero, the callers cannot do anything sane with a 0 return. They should return an error which means future calls to GUP will not succeed, or they should return some non-zero number of pinned pages which means GUP should be called again. If start + nr_pages overflows it should return -EOVERFLOW to signal the arguments are invalid. Syzkaller keeps tripping on this when fuzzing GUP arguments. Link: https://lkml.kernel.org/r/[email protected] Signed-off-by: Jason Gunthorpe <[email protected]> Reported-by: [email protected] Closes: https://lore.kernel.org/all/[email protected] Reviewed-by: John Hubbard <[email protected]> Reviewed-by: Lorenzo Stoakes <[email protected]> Reviewed-by: David Hildenbrand <[email protected]> Signed-off-by: Andrew Morton <[email protected]>