diff mbox series

[bpf] bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets

Message ID 20230920102055.42662-1-jakub@cloudflare.com (mailing list archive)
State Accepted
Commit b80e31baa43614e086a9d29dc1151932b1bd7fc5
Delegated to: BPF
Headers show
Series [bpf] bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets | expand

Checks

Context Check Description
bpf/vmtest-bpf-PR success PR summary
netdev/series_format success Single patches do not need cover letters
netdev/tree_selection success Clearly marked for bpf
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1342 this patch: 1342
netdev/cc_maintainers warning 4 maintainers not CCed: edumazet@google.com pabeni@redhat.com kuba@kernel.org davem@davemloft.net
netdev/build_clang success Errors and warnings before: 1364 this patch: 1364
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
netdev/build_allmodconfig_warn success Errors and warnings before: 1365 this patch: 1365
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 16 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-VM_Test-2 success Logs for build for s390x with gcc
bpf/vmtest-bpf-VM_Test-20 success Logs for test_progs_no_alu32_parallel on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-23 success Logs for test_progs_parallel on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-24 success Logs for test_verifier on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-26 success Logs for test_verifier on x86_64 with gcc
bpf/vmtest-bpf-VM_Test-27 success Logs for test_verifier on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-28 success Logs for veristat
bpf/vmtest-bpf-VM_Test-6 success Logs for test_maps on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-9 success Logs for test_maps on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-8 success Logs for test_maps on x86_64 with gcc
bpf/vmtest-bpf-VM_Test-10 success Logs for test_progs on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-12 success Logs for test_progs on x86_64 with gcc
bpf/vmtest-bpf-VM_Test-14 success Logs for test_progs_no_alu32 on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-13 success Logs for test_progs on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-16 success Logs for test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-VM_Test-17 success Logs for test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-18 success Logs for test_progs_no_alu32_parallel on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-19 success Logs for test_progs_no_alu32_parallel on x86_64 with gcc
bpf/vmtest-bpf-VM_Test-21 success Logs for test_progs_parallel on aarch64 with gcc
bpf/vmtest-bpf-VM_Test-22 success Logs for test_progs_parallel on x86_64 with gcc
bpf/vmtest-bpf-VM_Test-25 success Logs for test_verifier on s390x with gcc
bpf/vmtest-bpf-VM_Test-15 success Logs for test_progs_no_alu32 on s390x with gcc
bpf/vmtest-bpf-VM_Test-11 success Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-VM_Test-7 success Logs for test_maps on s390x with gcc
bpf/vmtest-bpf-VM_Test-0 success Logs for ShellCheck
bpf/vmtest-bpf-VM_Test-4 success Logs for build for x86_64 with llvm-16
bpf/vmtest-bpf-VM_Test-5 success Logs for set-matrix
bpf/vmtest-bpf-VM_Test-3 success Logs for build for x86_64 with gcc
bpf/vmtest-bpf-VM_Test-1 success Logs for build for aarch64 with gcc

Commit Message

Jakub Sitnicki Sept. 20, 2023, 10:20 a.m. UTC 
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 122e6c79efe1 ("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: 122e6c79efe1 ("sock_map: Update sock type checks for UDP")
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
FYI, I'm working on revamping the sockmap_listen selftest, which exercises
some of redirect combinations, to cover the whole combination matrix so
that we can catch these kinds of problems early on.

 net/core/sock_map.c | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Kui-Feng Lee Sept. 20, 2023, 6:19 p.m. UTC | #1 
On 9/20/23 03:20, Jakub Sitnicki wrote:
> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index cb11750b1df5..4292c2ed1828 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -668,6 +668,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
>   	sk = __sock_map_lookup_elem(map, key);
>   	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>   		return SK_DROP;
> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
> +		return SK_DROP;
>   
>   	msg->flags = flags;
>   	msg->sk_redir = sk;
> @@ -1267,6 +1269,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
>   	sk = __sock_hash_lookup_elem(map, key);
>   	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>   		return SK_DROP;
> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
> +		return SK_DROP;
>   
>   	msg->flags = flags;
>   	msg->sk_redir = sk;

Just be curious! Can it happen to other socket types?
I mean to redirect a msg from a sk of any type to one of another type.
Jakub Sitnicki Sept. 20, 2023, 8:59 p.m. UTC | #2 
On Wed, Sep 20, 2023 at 11:19 AM -07, Kui-Feng Lee wrote:
> On 9/20/23 03:20, Jakub Sitnicki wrote:
>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>> index cb11750b1df5..4292c2ed1828 100644
>> --- a/net/core/sock_map.c
>> +++ b/net/core/sock_map.c
>> @@ -668,6 +668,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
>>   	sk = __sock_map_lookup_elem(map, key);
>>   	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>>   		return SK_DROP;
>> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
>> +		return SK_DROP;
>>     	msg->flags = flags;
>>   	msg->sk_redir = sk;
>> @@ -1267,6 +1269,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
>>   	sk = __sock_hash_lookup_elem(map, key);
>>   	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>>   		return SK_DROP;
>> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
>> +		return SK_DROP;
>>     	msg->flags = flags;
>>   	msg->sk_redir = sk;
>
> Just be curious! Can it happen to other socket types?
> I mean to redirect a msg from a sk of any type to one of another type.

Today sk_msg redirects are implemented only for tcp4 and tcp6.

Here's a full matrix of what redirects are supported [1].

[1] https://gist.github.com/jsitnicki/578fdd614d181bed2b02922b17972b4e
Kui-Feng Lee Sept. 20, 2023, 9:11 p.m. UTC | #3 
On 9/20/23 13:59, Jakub Sitnicki wrote:
> On Wed, Sep 20, 2023 at 11:19 AM -07, Kui-Feng Lee wrote:
>> On 9/20/23 03:20, Jakub Sitnicki wrote:
>>> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
>>> index cb11750b1df5..4292c2ed1828 100644
>>> --- a/net/core/sock_map.c
>>> +++ b/net/core/sock_map.c
>>> @@ -668,6 +668,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
>>>    	sk = __sock_map_lookup_elem(map, key);
>>>    	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>>>    		return SK_DROP;
>>> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
>>> +		return SK_DROP;
>>>      	msg->flags = flags;
>>>    	msg->sk_redir = sk;
>>> @@ -1267,6 +1269,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
>>>    	sk = __sock_hash_lookup_elem(map, key);
>>>    	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>>>    		return SK_DROP;
>>> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
>>> +		return SK_DROP;
>>>      	msg->flags = flags;
>>>    	msg->sk_redir = sk;
>>
>> Just be curious! Can it happen to other socket types?
>> I mean to redirect a msg from a sk of any type to one of another type.
> 
> Today sk_msg redirects are implemented only for tcp4 and tcp6.
> 
> Here's a full matrix of what redirects are supported [1].
> 
> [1] https://gist.github.com/jsitnicki/578fdd614d181bed2b02922b17972b4e

Thanks!
John Fastabend Sept. 25, 2023, 6:27 p.m. UTC | #4 
Jakub Sitnicki wrote:
> 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 122e6c79efe1 ("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: 122e6c79efe1 ("sock_map: Update sock type checks for UDP")
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
> FYI, I'm working on revamping the sockmap_listen selftest, which exercises
> some of redirect combinations, to cover the whole combination matrix so
> that we can catch these kinds of problems early on.

Yes this would be appreciated.

> 
>  net/core/sock_map.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index cb11750b1df5..4292c2ed1828 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -668,6 +668,8 @@ BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
>  	sk = __sock_map_lookup_elem(map, key);
>  	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>  		return SK_DROP;
> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
> +		return SK_DROP;
>  
>  	msg->flags = flags;
>  	msg->sk_redir = sk;
> @@ -1267,6 +1269,8 @@ BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
>  	sk = __sock_hash_lookup_elem(map, key);
>  	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
>  		return SK_DROP;
> +	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
> +		return SK_DROP;

As a stop gap I think this is fine. If anyone wants to add support though
I do think as a use case it would make sense to redirect TCP into an
AF_UNIX socket and vice versa.

Acked-by: John Fastabend <john.fastabend@gmail.com>
patchwork-bot+netdevbpf@kernel.org Sept. 29, 2023, 3:20 p.m. UTC | #5 
Hello:

This patch was applied to bpf/bpf.git (master)
by Daniel Borkmann <daniel@iogearbox.net>:

On Wed, 20 Sep 2023 12:20:55 +0200 you wrote:
> 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
> 
> [...]

Here is the summary with links:
  - [bpf] bpf, sockmap: Reject sk_msg egress redirects to non-TCP sockets
    https://git.kernel.org/bpf/bpf/c/b80e31baa436

You are awesome, thank you!
diff mbox series

Patch

diff --git a/net/core/sock_map.c b/net/core/sock_map.c
index cb11750b1df5..4292c2ed1828 100644
--- a/net/core/sock_map.c
+++ b/net/core/sock_map.c
@@ -668,6 +668,8 @@  BPF_CALL_4(bpf_msg_redirect_map, struct sk_msg *, msg,
 	sk = __sock_map_lookup_elem(map, key);
 	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
 		return SK_DROP;
+	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
+		return SK_DROP;
 
 	msg->flags = flags;
 	msg->sk_redir = sk;
@@ -1267,6 +1269,8 @@  BPF_CALL_4(bpf_msg_redirect_hash, struct sk_msg *, msg,
 	sk = __sock_hash_lookup_elem(map, key);
 	if (unlikely(!sk || !sock_map_redirect_allowed(sk)))
 		return SK_DROP;
+	if (!(flags & BPF_F_INGRESS) && !sk_is_tcp(sk))
+		return SK_DROP;
 
 	msg->flags = flags;
 	msg->sk_redir = sk;