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

[Tetsuo Handa]

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);
}