Re: [syzbot] [mm?] general protection fault in shmem_get_next_id

[Hillf Danton <hdanton@sina.com>]

On Mon, 01 Apr 2024 23:58:20 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    fe46a7dd189e Merge tag 'sound-6.9-rc1' of git://git.kernel..
> git tree:       upstream
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=150d3cee180000

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git  fe46a7dd189e

--- x/mm/shmem_quota.c
+++ y/mm/shmem_quota.c
@@ -116,7 +116,7 @@ static int shmem_free_file_info(struct s
 static int shmem_get_next_id(struct super_block *sb, struct kqid *qid)
 {
 	struct mem_dqinfo *info = sb_dqinfo(sb, qid->type);
-	struct rb_node *node = ((struct rb_root *)info->dqi_priv)->rb_node;
+	struct rb_node *node;
 	qid_t id = from_kqid(&init_user_ns, *qid);
 	struct quota_info *dqopt = sb_dqopt(sb);
 	struct quota_id *entry = NULL;
@@ -126,6 +126,11 @@ static int shmem_get_next_id(struct supe
 		return -ESRCH;
 
 	down_read(&dqopt->dqio_sem);
+	if (!info->dqi_priv) {
+		ret = -ENOENT;
+		goto out_unlock;
+	}
+	node = ((struct rb_root *)info->dqi_priv)->rb_node;
 	while (node) {
 		entry = rb_entry(node, struct quota_id, node);
 
--