linux-stable.git/kernel/bpf/sockmap.c, branch v4.18.8

bpf, sockmap: fix leakage of smap_psock_map_entry

2018-09-15T07:46:48+00:00

[ Upstream commit d40b0116c94bd8fc2b63aae35ce8e66bb53bba42 ]

While working on sockmap I noticed that we do not always kfree the
struct smap_psock_map_entry list elements which track psocks attached
to maps. In the case of sock_hash_ctx_update_elem(), these map entries
are allocated outside of __sock_map_ctx_update_elem() with their
linkage to the socket hash table filled. In the case of sock array,
the map entries are allocated inside of __sock_map_ctx_update_elem()
and added with their linkage to the psock->maps. Both additions are
under psock->maps_lock each.

Now, we drop these elements from their psock->maps list in a few
occasions: i) in sock array via smap_list_map_remove() when an entry
is either deleted from the map from user space, or updated via
user space or BPF program where we drop the old socket at that map
slot, or the sock array is freed via sock_map_free() and drops all
its elements; ii) for sock hash via smap_list_hash_remove() in exactly
the same occasions as just described for sock array; iii) in the
bpf_tcp_close() where we remove the elements from the list via
psock_map_pop() and iterate over them dropping themselves from either
sock array or sock hash; and last but not least iv) once again in
smap_gc_work() which is a callback for deferring the work once the
psock refcount hit zero and thus the socket is being destroyed.

Problem is that the only case where we kfree() the list entry is
in case iv), which at that point should have an empty list in
normal cases. So in cases from i) to iii) we unlink the elements
without freeing where they go out of reach from us. Hence fix is
to properly kfree() them as well to stop the leakage. Given these
are all handled under psock->maps_lock there is no need for deferred
RCU freeing.

I later also ran with kmemleak detector and it confirmed the finding
as well where in the state before the fix the object goes unreferenced
while after the patch no kmemleak report related to BPF showed up.

  [...]
  unreferenced object 0xffff880378eadae0 (size 64):
    comm "test_sockmap", pid 2225, jiffies 4294720701 (age 43.504s)
    hex dump (first 32 bytes):
      00 01 00 00 00 00 ad de 00 02 00 00 00 00 ad de  ................
      50 4d 75 5d 03 88 ff ff 00 00 00 00 00 00 00 00  PMu]............
    backtrace:
      [<000000005225ac3c>] sock_map_ctx_update_elem.isra.21+0xd8/0x210
      [<0000000045dd6d3c>] bpf_sock_map_update+0x29/0x60
      [<00000000877723aa>] ___bpf_prog_run+0x1e1f/0x4960
      [<000000002ef89e83>] 0xffffffffffffffff
  unreferenced object 0xffff880378ead240 (size 64):
    comm "test_sockmap", pid 2225, jiffies 4294720701 (age 43.504s)
    hex dump (first 32 bytes):
      00 01 00 00 00 00 ad de 00 02 00 00 00 00 ad de  ................
      00 44 75 5d 03 88 ff ff 00 00 00 00 00 00 00 00  .Du]............
    backtrace:
      [<000000005225ac3c>] sock_map_ctx_update_elem.isra.21+0xd8/0x210
      [<0000000030e37a3a>] sock_map_update_elem+0x125/0x240
      [<000000002e5ce36e>] map_update_elem+0x4eb/0x7b0
      [<00000000db453cc9>] __x64_sys_bpf+0x1f9/0x360
      [<0000000000763660>] do_syscall_64+0x9a/0x300
      [<00000000422a2bb2>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
      [<000000002ef89e83>] 0xffffffffffffffff
  [...]

Fixes: e9db4ef6bf4c ("bpf: sockhash fix omitted bucket lock in sock_close")
Fixes: 54fedb42c653 ("bpf: sockmap, fix smap_list_map_remove when psock is in many maps")
Fixes: 2f857d04601a ("bpf: sockmap, remove STRPARSER map_flags and add multi-map support")
Signed-off-by: Daniel Borkmann 
Acked-by: John Fastabend 
Acked-by: Song Liu 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

bpf, sockmap: fix sock_map_ctx_update_elem race with exist/noexist

2018-09-15T07:46:48+00:00

[ Upstream commit 585f5a6252ee43ec8feeee07387e3fcc7e8bb292 ]

The current code in sock_map_ctx_update_elem() allows for BPF_EXIST
and BPF_NOEXIST map update flags. While on array-like maps this approach
is rather uncommon, e.g. bpf_fd_array_map_update_elem() and others
enforce map update flags to be BPF_ANY such that xchg() can be used
directly, the current implementation in sock map does not guarantee
that such operation with BPF_EXIST / BPF_NOEXIST is atomic.

The initial test does a READ_ONCE(stab->sock_map[i]) to fetch the
socket from the slot which is then tested for NULL / non-NULL. However
later after __sock_map_ctx_update_elem(), the actual update is done
through osock = xchg(&stab->sock_map[i], sock). Problem is that in
the meantime a different CPU could have updated / deleted a socket
on that specific slot and thus flag contraints won't hold anymore.

I've been thinking whether best would be to just break UAPI and do
an enforcement of BPF_ANY to check if someone actually complains,
however trouble is that already in BPF kselftest we use BPF_NOEXIST
for the map update, and therefore it might have been copied into
applications already. The fix to keep the current behavior intact
would be to add a map lock similar to the sock hash bucket lock only
for covering the whole map.

Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
Signed-off-by: Daniel Borkmann 
Acked-by: John Fastabend 
Acked-by: Song Liu 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

bpf, sockmap: fix map elem deletion race with smap_stop_sock

2018-09-15T07:46:48+00:00

[ Upstream commit 166ab6f0a0702fdd4d865ad5090bf3094ed83428 ]

The smap_start_sock() and smap_stop_sock() are each protected under
the sock->sk_callback_lock from their call-sites except in the case
of sock_map_delete_elem() where we drop the old socket from the map
slot. This is racy because the same sock could be part of multiple
sock maps, so we run smap_stop_sock() in parallel, and given at that
point psock->strp_enabled might be true on both CPUs, we might for
example wrongly restore the sk->sk_data_ready / sk->sk_write_space.
Therefore, hold the sock->sk_callback_lock as well on delete. Looks
like 2f857d04601a ("bpf: sockmap, remove STRPARSER map_flags and add
multi-map support") had this right, but later on e9db4ef6bf4c ("bpf:
sockhash fix omitted bucket lock in sock_close") removed it again
from delete leaving this smap_stop_sock() instance unprotected.

Fixes: e9db4ef6bf4c ("bpf: sockhash fix omitted bucket lock in sock_close")
Signed-off-by: Daniel Borkmann 
Acked-by: John Fastabend 
Acked-by: Song Liu 
Signed-off-by: Alexei Starovoitov 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

bpf, sockmap: fix leak in bpf_tcp_sendmsg wait for mem path

2018-08-08T19:06:17+00:00

In bpf_tcp_sendmsg() the sk_alloc_sg() may fail. In the case of
ENOMEM, it may also mean that we've partially filled the scatterlist
entries with pages. Later jumping to sk_stream_wait_memory()
we could further fail with an error for several reasons, however
we miss to call free_start_sg() if the local sk_msg_buff was used.

Fixes: 4f738adba30a ("bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data")
Signed-off-by: Daniel Borkmann 
Acked-by: John Fastabend 
Signed-off-by: Alexei Starovoitov

bpf, sockmap: fix bpf_tcp_sendmsg sock error handling

2018-08-08T19:06:17+00:00

While working on bpf_tcp_sendmsg() code, I noticed that when a
sk->sk_err is set we error out with err = sk->sk_err. However
this is problematic since sk->sk_err is a positive error value
and therefore we will neither go into sk_stream_error() nor will
we report an error back to user space. I had this case with EPIPE
and user space was thinking sendmsg() succeeded since EPIPE is
a positive value, thinking we submitted 32 bytes. Fix it by
negating the sk->sk_err value.

Fixes: 4f738adba30a ("bpf: create tcp_bpf_ulp allowing BPF to monitor socket TX/RX data")
Signed-off-by: Daniel Borkmann 
Acked-by: John Fastabend 
Signed-off-by: Alexei Starovoitov

bpf: sockmap, convert bpf_compute_data_pointers to bpf_*_sk_skb

2018-07-07T22:19:30+00:00

In commit

  'bpf: bpf_compute_data uses incorrect cb structure' (8108a7751512)

we added the routine bpf_compute_data_end_sk_skb() to compute the
correct data_end values, but this has since been lost. In kernel
v4.14 this was correct and the above patch was applied in it
entirety. Then when v4.14 was merged into v4.15-rc1 net-next tree
we lost the piece that renamed bpf_compute_data_pointers to the
new function bpf_compute_data_end_sk_skb. This was done here,

e1ea2f9856b7 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net")

When it conflicted with the following rename patch,

6aaae2b6c433 ("bpf: rename bpf_compute_data_end into bpf_compute_data_pointers")

Finally, after a refactor I thought even the function
bpf_compute_data_end_sk_skb() was no longer needed and it was
erroneously removed.

However, we never reverted the sk_skb_convert_ctx_access() usage of
tcp_skb_cb which had been committed and survived the merge conflict.
Here we fix this by adding back the helper and *_data_end_sk_skb()
usage. Using the bpf_skc_data_end mapping is not correct because it
expects a qdisc_skb_cb object but at the sock layer this is not the
case. Even though it happens to work here because we don't overwrite
any data in-use at the socket layer and the cb structure is cleared
later this has potential to create some subtle issues. But, even
more concretely the filter.c access check uses tcp_skb_cb.

And by some act of chance though,

struct bpf_skb_data_end {
        struct qdisc_skb_cb        qdisc_cb;             /*     0    28 */

        /* XXX 4 bytes hole, try to pack */

        void *                     data_meta;            /*    32     8 */
        void *                     data_end;             /*    40     8 */

        /* size: 48, cachelines: 1, members: 3 */
        /* sum members: 44, holes: 1, sum holes: 4 */
        /* last cacheline: 48 bytes */
};

and then tcp_skb_cb,

struct tcp_skb_cb {
	[...]
                struct {
                        __u32      flags;                /*    24     4 */
                        struct sock * sk_redir;          /*    32     8 */
                        void *     data_end;             /*    40     8 */
                } bpf;                                   /*          24 */
        };

So when we use offset_of() to track down the byte offset we get 40 in
either case and everything continues to work. Fix this mess and use
correct structures its unclear how long this might actually work for
until someone moves the structs around.

Reported-by: Martin KaFai Lau 
Fixes: e1ea2f9856b7 ("Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net")
Fixes: 6aaae2b6c433 ("bpf: rename bpf_compute_data_end into bpf_compute_data_pointers")
Signed-off-by: John Fastabend 
Signed-off-by: Alexei Starovoitov

bpf: sockmap, consume_skb in close path

2018-07-07T22:19:30+00:00

Currently, when a sock is closed and the bpf_tcp_close() callback is
used we remove memory but do not free the skb. Call consume_skb() if
the skb is attached to the buffer.

Reported-by: syzbot+d464d2c20c717ef5a6a8@syzkaller.appspotmail.com
Fixes: 1aa12bdf1bfb ("bpf: sockmap, add sock close() hook to remove socks")
Signed-off-by: John Fastabend 
Signed-off-by: Alexei Starovoitov

bpf: sockhash, disallow bpf_tcp_close and update in parallel

2018-07-07T22:19:30+00:00

After latest lock updates there is no longer anything preventing a
close and recvmsg call running in parallel. Additionally, we can
race update with close if we close a socket and simultaneously update
if via the BPF userspace API (note the cgroup ops are already run
with sock_lock held).

To resolve this take sock_lock in close and update paths.

Reported-by: syzbot+b680e42077a0d7c9a0c4@syzkaller.appspotmail.com
Fixes: e9db4ef6bf4c ("bpf: sockhash fix omitted bucket lock in sock_close")
Signed-off-by: John Fastabend 
Signed-off-by: Alexei Starovoitov

bpf: sockmap, hash table is RCU so readers do not need locks

2018-07-07T22:16:58+00:00

This removes locking from readers of RCU hash table. Its not
necessary.

Fixes: 81110384441a ("bpf: sockmap, add hash map support")
Signed-off-by: John Fastabend 
Signed-off-by: Alexei Starovoitov

bpf: sockmap, error path can not release psock in multi-map case

2018-07-07T22:16:58+00:00

The current code, in the error path of sock_hash_ctx_update_elem,
checks if the sock has a psock in the user data and if so decrements
the reference count of the psock. However, if the error happens early
in the error path we may have never incremented the psock reference
count and if the psock exists because the sock is in another map then
we may inadvertently decrement the reference count.

Fix this by making the error path only call smap_release_sock if the
error happens after the increment.

Reported-by: syzbot+d464d2c20c717ef5a6a8@syzkaller.appspotmail.com
Fixes: 81110384441a ("bpf: sockmap, add hash map support")
Signed-off-by: John Fastabend 
Signed-off-by: Alexei Starovoitov