[PATCH] mm: mremap - Fix extent calculation

[Kalesh Singh]

When `next < old_addr`, `next - old_addr` arithmetic underflows
causing `extent` to be incorrect.

Make `extent` the smaller of `next - old_addr` or `old_end - old_addr`.

Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Signed-off-by: Kalesh Singh <kaleshsingh@xxxxxxxxxx>
---
 mm/mremap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/mremap.c b/mm/mremap.c
index c5590afe7165..f554320281cc 100644
--- a/mm/mremap.c
+++ b/mm/mremap.c
@@ -358,7 +358,9 @@ static unsigned long get_extent(enum pgt_entry entry, unsigned long old_addr,
 
 	next = (old_addr + size) & mask;
 	/* even if next overflowed, extent below will be ok */
-	extent = (next > old_end) ? old_end - old_addr : next - old_addr;
+	extent = next - old_addr;
+	if (extent > old_end - old_addr)
+		extent = old_end - old_addr;
 	next = (new_addr + size) & mask;
 	if (extent > next - new_addr)
 		extent = next - new_addr;
-- 
2.29.2.729.g45daf8777d-goog