[PATCH] mm/gup: Do not return 0 from pin_user_pages_fast() for bad args

[Jason Gunthorpe <jgg@nvidia.com>]

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.

Reported-by: syzbot+353c7be4964c6253f24a@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000094fdd05faa4d3a4@google.com
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 mm/gup.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/gup.c b/mm/gup.c
index bbe4162365933e..36c587fec574fd 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2969,7 +2969,7 @@ static int internal_get_user_pages_fast(unsigned long start,
 	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)))

base-commit: b3eacbbcd0dab69ed4c44cbd2d2d72b016762b17
-- 
2.40.1