From: Jason Gunthorpe <jgg@xxxxxxxxxx> commit 9883c7f84053cec2826ca3c56254601b5ce9cdbe upstream. 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/0-v1-3d5ed1f20d50+104-gup_overflow_jgg@xxxxxxxxxx Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Reported-by: syzbot+353c7be4964c6253f24a@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lore.kernel.org/all/000000000000094fdd05faa4d3a4@xxxxxxxxxx Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx> Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/gup.c +++ b/mm/gup.c @@ -2977,7 +2977,7 @@ static int internal_get_user_pages_fast( start = untagged_addr(start) & PAGE_MASK; len = nr_pages << PAGE_SHIFT; if (check_add_overflow(start, len, &end)) - return 0; + return -EOVERFLOW; if (end > TASK_SIZE_MAX) return -EFAULT; if (unlikely(!access_ok((void __user *)start, len)))
