Re: KASAN: use-after-free Read in corrupted

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Dmitry Vyukov wrote:
> This looks very similar to "KASAN: use-after-free Read in fuse_kill_sb_blk":
> https://groups.google.com/d/msg/syzkaller-bugs/4C4oiBX8vZ0/0NTQRcUYBgAJ
> 
> which you fixed with "fuse: don't keep dead fuse_conn at fuse_fill_super().":
> https://groups.google.com/d/msg/syzkaller-bugs/4C4oiBX8vZ0/W6pi8NdbBgAJ
> 
> However, here we have use-after-free in fuse_kill_sb_anon instead of
> use_kill_sb_blk. Do you think your patch will fix this as well?

Yes, for fuse_kill_sb_anon() and fuse_kill_sb_blk() are symmetrical.
I'm waiting for Miklos Szeredi to apply that patch.

static inline struct fuse_conn *get_fuse_conn_super(struct super_block *sb)
{
	return sb->s_fs_info;
}

static struct file_system_type fuse_fs_type = {
	.owner          = THIS_MODULE,
	.name           = "fuse",
	.fs_flags       = FS_HAS_SUBTYPE,
	.mount          = fuse_mount,
	.kill_sb        = fuse_kill_sb_anon,
};

static struct file_system_type fuseblk_fs_type = {
	.owner          = THIS_MODULE,
	.name           = "fuseblk",
	.mount          = fuse_mount_blk,
	.kill_sb        = fuse_kill_sb_blk,
	.fs_flags       = FS_REQUIRES_DEV | FS_HAS_SUBTYPE,
};

static void fuse_kill_sb_anon(struct super_block *sb)
{
	struct fuse_conn *fc = get_fuse_conn_super(sb);

	if (fc) {
		down_write(&fc->killsb);
		fc->sb = NULL;
		up_write(&fc->killsb);
	}

	kill_anon_super(sb);
}

static void fuse_kill_sb_blk(struct super_block *sb)
{
	struct fuse_conn *fc = get_fuse_conn_super(sb);

	if (fc) {
		down_write(&fc->killsb);
		fc->sb = NULL;
		up_write(&fc->killsb);
	}

	kill_block_super(sb);
}