c->btree_roots_known[i].b can be NULL. In this case, a NULL pointer dereference
occurs, so you need to add code to check the variable.

Reported-by: syzbot+b468b9fef56949c3b528@syzkaller.appspotmail.com
Fixes: ("bcachefs: metadata version bucket_stripe_sectors")
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 fs/bcachefs/sb-downgrade.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/bcachefs/sb-downgrade.c b/fs/bcachefs/sb-downgrade.c
index ae715ff658e8..8767c33c2b51 100644
--- a/fs/bcachefs/sb-downgrade.c
+++ b/fs/bcachefs/sb-downgrade.c
@@ -143,6 +143,9 @@ UPGRADE_TABLE()
 
 static int have_stripes(struct bch_fs *c)
 {
+	if (IS_ERR_OR_NULL(c->btree_roots_known[BTREE_ID_stripes].b))
+		return 0;
+
 	return !btree_node_fake(c->btree_roots_known[BTREE_ID_stripes].b);
 }
 
--

On Thu, Oct 24, 2024 at 01:13:45AM +0900, Jeongjun Park wrote:
> c->btree_roots_known[i].b can be NULL. In this case, a NULL pointer dereference
> occurs, so you need to add code to check the variable.
> 
> Reported-by: syzbot+b468b9fef56949c3b528@syzkaller.appspotmail.com
> Fixes: ("bcachefs: metadata version bucket_stripe_sectors")
> Signed-off-by: Jeongjun Park <aha310510@gmail.com>

Thanks, applied