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  1. 29 Sep, 2023 4 commits
    • Jakub Sitnicki's avatar
      bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets · b80e31ba
      Jakub Sitnicki authored 
      With a SOCKMAP/SOCKHASH map and an sk_msg program user can steer messages
sent from one TCP socket (s1) to actually egress from another TCP
socket (s2):

tcp_bpf_sendmsg(s1)		// = sk_prot->sendmsg
  tcp_bpf_send_verdict(s1)	// __SK_REDIRECT case
    tcp_bpf_sendmsg_redir(s2)
      tcp_bpf_push_locked(s2)
	tcp_bpf_push(s2)
	  tcp_rate_check_app_limited(s2) // expects tcp_sock
	  tcp_sendmsg_locked(s2)	 // ditto

There is a hard-coded assumption in the call-chain, that the egress
socket (s2) is a TCP socket.

However in commit 122e6c79 ("sock_map: Update sock type checks for
UDP") we have enabled redirects to non-TCP sockets. This was done for the
sake of BPF sk_skb programs. There was no indention to support sk_msg
send-to-egress use case.

As a result, attempts to send-to-egress through a non-TCP socket lead to a
crash due to invalid downcast from sock to tcp_sock:

 BUG: kernel NULL pointer dereference, address: 000000000000002f
 ...
 Call Trace:
  <TASK>
  ? show_regs+0x60/0x70
  ? __die+0x1f/0x70
  ? page_fault_oops+0x80/0x160
  ? do_user_addr_fault+0x2d7/0x800
  ? rcu_is_watching+0x11/0x50
  ? exc_page_fault+0x70/0x1c0
  ? asm_exc_page_fault+0x27/0x30
  ? tcp_tso_segs+0x14/0xa0
  tcp_write_xmit+0x67/0xce0
  __tcp_push_pending_frames+0x32/0xf0
  tcp_push+0x107/0x140
  tcp_sendmsg_locked+0x99f/0xbb0
  tcp_bpf_push+0x19d/0x3a0
  tcp_bpf_sendmsg_redir+0x55/0xd0
  tcp_bpf_send_verdict+0x407/0x550
  tcp_bpf_sendmsg+0x1a1/0x390
  inet_sendmsg+0x6a/0x70
  sock_sendmsg+0x9d/0xc0
  ? sockfd_lookup_light+0x12/0x80
  __sys_sendto+0x10e/0x160
  ? syscall_enter_from_user_mode+0x20/0x60
  ? __this_cpu_preempt_check+0x13/0x20
  ? lockdep_hardirqs_on+0x82/0x110
  __x64_sys_sendto+0x1f/0x30
  do_syscall_64+0x38/0x90
  entry_SYSCALL_64_after_hwframe+0x63/0xcd

Reject selecting a non-TCP sockets as redirect target from a BPF sk_msg
program to prevent the crash. When attempted, user will receive an EACCES
error from send/sendto/sendmsg() syscall.

Fixes: 122e6c79 ("sock_map: Update sock type checks for UDP")
Signed-off-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20230920102055.42662-1-jakub@cloudflare.com
      b80e31ba
    • John Fastabend's avatar
      bpf, sockmap: Add tests for MSG_F_PEEK · 5f405c0c
      John Fastabend authored 
      Test that we can read with MSG_F_PEEK and then still get correct number
of available bytes through FIONREAD. The recv() (without PEEK) then
returns the bytes as expected. The recv() always worked though because
it was just the available byte reporting that was broke before latest
fixes.
Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-4-john.fastabend@gmail.com
      5f405c0c
    • John Fastabend's avatar
      bpf, sockmap: Do not inc copied_seq when PEEK flag set · da9e915e
      John Fastabend authored 
      When data is peek'd off the receive queue we shouldn't considered it
copied from tcp_sock side. When we increment copied_seq this will confuse
tcp_data_ready() because copied_seq can be arbitrarily increased. From
application side it results in poll() operations not waking up when
expected.

Notice tcp stack without BPF recvmsg programs also does not increment
copied_seq.

We broke this when we moved copied_seq into recvmsg to only update when
actual copy was happening. But, it wasn't working correctly either before
because the tcp_data_ready() tried to use the copied_seq value to see
if data was read by user yet. See fixes tags.

Fixes: e5c6de5f ("bpf, sockmap: Incorrectly handling copied_seq")
Fixes: 04919bed ("tcp: Introduce tcp_read_skb()")
Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-3-john.fastabend@gmail.com
      da9e915e
    • John Fastabend's avatar
      bpf: tcp_read_skb needs to pop skb regardless of seq · 9b7177b1
      John Fastabend authored 
      Before fix e5c6de5f tcp_read_skb() would increment the tp->copied-seq
value. This (as described in the commit) would cause an error for apps
because once that is incremented the application might believe there is no
data to be read. Then some apps would stall or abort believing no data is
available.

However, the fix is incomplete because it introduces another issue in
the skb dequeue. The loop does tcp_recv_skb() in a while loop to consume
as many skbs as possible. The problem is the call is ...

  tcp_recv_skb(sk, seq, &offset)

... where 'seq' is:

  u32 seq = tp->copied_seq;

Now we can hit a case where we've yet incremented copied_seq from BPF side,
but then tcp_recv_skb() fails this test ...

 if (offset < skb->len || (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN))

... so that instead of returning the skb we call tcp_eat_recv_skb() which
frees the skb. This is because the routine believes the SKB has been collapsed
per comment:

 /* This looks weird, but this can happen if TCP collapsing
  * splitted a fat GRO packet, while we released socket lock
  * in skb_splice_bits()
  */

This can't happen here we've unlinked the full SKB and orphaned it. Anyways
it would confuse any BPF programs if the data were suddenly moved underneath
it.

To fix this situation do simpler operation and just skb_peek() the data
of the queue followed by the unlink. It shouldn't need to check this
condition and tcp_read_skb() reads entire skbs so there is no need to
handle the 'offset!=0' case as we would see in tcp_read_sock().

Fixes: e5c6de5f ("bpf, sockmap: Incorrectly handling copied_seq")
Fixes: 04919bed ("tcp: Introduce tcp_read_skb()")
Signed-off-by: default avatarJohn Fastabend <john.fastabend@gmail.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reviewed-by: default avatarJakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20230926035300.135096-2-john.fastabend@gmail.com
      9b7177b1
  3. 20 Sep, 2023 1 commit
  5. 19 Sep, 2023 5 commits
  7. 18 Sep, 2023 22 commits
  9. 17 Sep, 2023 3 commits
  11. 16 Sep, 2023 4 commits
  13. 15 Sep, 2023 1 commit
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