[PATCH 22/46] mm/gup: check for overflow when converting nr_pages to bytes in GUP-fast

[David Hildenbrand (Arm)]

The overflow check in gup_fast_fallback() only covers the addition to
start. The preceding nr_pages << PAGE_SHIFT can already have truncated
the length on 32bit.

Users such as RapidIO's rio_dma_transfer() can derive such page counts
from a 64-bit userspace length.

Let's just check_shl_overflow() to reject any such overflow with
-EOVERFLOW early.

Fixes: c28b1fc70390 ("mm/gup: reorganize internal_get_user_pages_fast()")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
 mm/gup.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 9906965893431..48e1bfe5ab9a9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -3214,8 +3214,8 @@ static int gup_fast_fallback(unsigned long start, unsigned long nr_pages,
 		might_lock_read(&current->mm->mmap_lock);
 
 	start = untagged_addr(start) & PAGE_MASK;
-	len = nr_pages << PAGE_SHIFT;
-	if (check_add_overflow(start, len, &end))
+	if (check_shl_overflow(nr_pages, PAGE_SHIFT, &len) ||
+	    check_add_overflow(start, len, &end))
 		return -EOVERFLOW;
 	if (end > TASK_SIZE_MAX)
 		return -EFAULT;

-- 
2.43.0