[PATCH] fuse: add a null-ptr check

[Nihar Chaithanya]

The bug KASAN: null-ptr-deref is triggered due to *val being
dereferenced when it is null in fuse_copy_do() when performing
memcpy().
Add a check in fuse_copy_one() to prevent this.

Reported-by: syzbot+87b8e6ed25dbc41759f7@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=87b8e6ed25dbc41759f7
Fixes: 3b97c3652d91 ("fuse: convert direct io to use folios")
Tested-by: syzbot+87b8e6ed25dbc41759f7@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Nihar Chaithanya <niharchaithanya@xxxxxxxxx>
---
 fs/fuse/dev.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 563a0bfa0e95..9c93759ac14b 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1070,6 +1070,9 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes,
 /* Copy a single argument in the request to/from userspace buffer */
 static int fuse_copy_one(struct fuse_copy_state *cs, void *val, unsigned size)
 {
+	if (!val)
+		return -EINVAL;
+
 	while (size) {
 		if (!cs->len) {
 			int err = fuse_copy_fill(cs);
-- 
2.34.1