[PATCH] mm/nommu: Reject wrapping ranges in access_remote_vm()

[Anastasios Papagiannis <tasos.papagiannnis@gmail.com>]

The NOMMU implementation of access_process_vm() rejects address ranges
whose end wraps around, but access_remote_vm() bypasses this check even
though both functions delegate to __access_remote_vm().

Move the wraparound check into __access_remote_vm() so it applies to
both entry points.

This is originally reported in [1].

[1] https://lore.kernel.org/bpf/4ef240a5bea36ff84df9589671367832860795159386a4c8fba546a0fa8b786f@mail.kernel.org/

Fixes: f55f199b7d76 ("NOMMU: implement access_remote_vm")
Signed-off-by: Anastasios Papagiannis <tasos.papagiannnis@gmail.com>
---
 mm/nommu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/nommu.c b/mm/nommu.c
index 498e01ee40b0..ed44510e3770 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1674,6 +1674,9 @@ static int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
 	struct vm_area_struct *vma;
 	int write = gup_flags & FOLL_WRITE;
 
+	if (addr + len < addr)
+		return 0;
+
 	if (mmap_read_lock_killable(mm))
 		return 0;
 
@@ -1727,9 +1730,6 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
 {
 	struct mm_struct *mm;
 
-	if (addr + len < addr)
-		return 0;
-
 	mm = get_task_mm(tsk);
 	if (!mm)
 		return 0;

base-commit: 0d9ff90a5422cc7509258aaaba1e7481df4d332a
-- 
2.55.0