On 8/18/20 3:27 AM, Martin KaFai Lau wrote:
> On Mon, Aug 03, 2020 at 06:46:53PM +0200, KP Singh wrote:
>> From: KP Singh <kpsingh@xxxxxxxxxx>
>>
>> Similar to bpf_local_storage for sockets, add local storage for inodes.
>> The life-cycle of storage is managed with the life-cycle of the inode.
>> i.e. the storage is destroyed along with the owning inode.
>>
>> The BPF LSM allocates an __rcu pointer to the bpf_local_storage in the
>> security blob which are now stackable and can co-exist with other LSMs.
>>
>> Signed-off-by: KP Singh <kpsingh@xxxxxxxxxx>
>> ---
>> include/linux/bpf_local_storage.h | 10 +
>> include/linux/bpf_lsm.h | 21 ++
>> include/linux/bpf_types.h | 3 +
>> include/uapi/linux/bpf.h | 38 +++
>> kernel/bpf/Makefile | 1 +
[...]
ata *inode_storage_lookup(struct inode *inode,
>> + struct bpf_map *map,
>> + bool cacheit_lockit)
>> +{
>> + struct bpf_local_storage *inode_storage;
>> + struct bpf_local_storage_map *smap;
>> + struct bpf_storage_blob *bsb;
>> +
>> + bsb = bpf_inode(inode);
>> + if (!bsb)
>> + return ERR_PTR(-ENOENT);
> ERR_PTR is returned here...
>
>> +
>> + inode_storage = rcu_dereference(bsb->storage);
>> + if (!inode_storage)
>> + return NULL;
>> +
[...]
>> + kfree_rcu(local_storage, rcu);
>> +}
>> +
>> +
>> +static void *bpf_fd_inode_storage_lookup_elem(struct bpf_map *map, void *key)
>> +{
>> + struct bpf_local_storage_data *sdata;
>> + struct file *f;
>> + int fd;
>> +
>> + fd = *(int *)key;
>> + f = fcheck(fd);
>> + if (!f)
>> + return ERR_PTR(-EINVAL);
>> +
>> + get_file(f);
>> + sdata = inode_storage_lookup(f->f_inode, map, true);
>> + fput(f);
>> + return sdata ? sdata->data : NULL;
> sdata can be ERR_PTR here and a few other cases below.
>
> May be inode_storage_lookup() should just return NULL.
I think returning NULL is a better option. Thanks!
>
>> +}
>> +
>> +static int bpf_fd_inode_storage_update_elem(struct bpf_map *map, void *key,
>> + void *value, u64 map_flags)
>> +{
>> + struct bpf_local_storage_data *sdata;
>> + struct file *f;
>> + int fd;
>> +
>> + fd = *(int *)key;
>> + f = fcheck(fd);
>> + if (!f)
>> + return -EINVAL;
>> +
>> + get_file(f);> get_file() does atomic_long_inc() instead of atomic_long_inc_not_zero().
> I don't see how that helps here. Am I missing something?
You are right, this should not not be an fcheck followed by a get_file
rather fcheck followed by get_file_rcu:
#define get_file_rcu_many(x, cnt) \
atomic_long_add_unless(&(x)->f_count, (cnt), 0)
#define get_file_rcu(x) get_file_rcu_many((x), 1)
#define file_count(x) atomic_long_read(&(x)->f_count)
But there is an easier way than all of this and this is to use
fget_raw which also calls get_file_rcu_many
and ensures a non-zero count before getting a reference.
- KP
>
>> + sdata = bpf_local_storage_update(f->f_inode, map, value, map_flags);
>> + fput(f);
>> + return PTR_ERR_OR_ZERO(sdata);
>> +}
>> +
