[PATCH net-next 0/2] Two BPF smap related followups

[PATCH net-next 0/2] Two BPF smap related followups

[Daniel Borkmann]

Fixing preemption imbalance and consolidating prologue
generation. Thanks!

Daniel Borkmann (2):
  bpf: don't enable preemption twice in smap_do_verdict
  bpf: reuse tc bpf prologue for sk skb progs

 kernel/bpf/sockmap.c |  3 ++-
 net/core/filter.c    | 47 ++++++++++-------------------------------------
 2 files changed, 12 insertions(+), 38 deletions(-)

-- 
1.9.3

[PATCH net-next 1/2] bpf: don't enable preemption twice in smap_do_verdict

[Daniel Borkmann]

In smap_do_verdict(), the fall-through branch leads to call
preempt_enable() twice for the SK_REDIRECT, which creates an
imbalance. Only enable it for all remaining cases again.

Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 kernel/bpf/sockmap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index f7e5e6c..39de541 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -135,7 +135,8 @@ static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
 	/* Fall through and free skb otherwise */
 	case SK_DROP:
 	default:
-		preempt_enable();
+		if (rc != SK_REDIRECT)
+			preempt_enable();
 		kfree_skb(skb);
 	}
 }
-- 
1.9.3

Re: [PATCH net-next 1/2] bpf: don't enable preemption twice in smap_do_verdict

[John Fastabend]

On 08/17/2017 08:22 AM, Daniel Borkmann wrote:
> In smap_do_verdict(), the fall-through branch leads to call
> preempt_enable() twice for the SK_REDIRECT, which creates an
> imbalance. Only enable it for all remaining cases again.
> 
> Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
> Reported-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> ---
>  kernel/bpf/sockmap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
> index f7e5e6c..39de541 100644
> --- a/kernel/bpf/sockmap.c
> +++ b/kernel/bpf/sockmap.c
> @@ -135,7 +135,8 @@ static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
>  	/* Fall through and free skb otherwise */
>  	case SK_DROP:
>  	default:
> -		preempt_enable();
> +		if (rc != SK_REDIRECT)
> +			preempt_enable();
>  		kfree_skb(skb);
>  	}
>  }
> 

Yep looks good, nice catch Alexei. Thanks! I'll add a selftests entry
in test_maps to catch this fall through case. Looks like we don't hit
this case during selftests at the moment.

Acked-by: John Fastabend <john.fastabend@gmail.com>

Re: [PATCH net-next 1/2] bpf: don't enable preemption twice in smap_do_verdict

[Alexei Starovoitov]

On 8/17/17 9:03 AM, John Fastabend wrote:
> On 08/17/2017 08:22 AM, Daniel Borkmann wrote:
>> In smap_do_verdict(), the fall-through branch leads to call
>> preempt_enable() twice for the SK_REDIRECT, which creates an
>> imbalance. Only enable it for all remaining cases again.
>>
>> Fixes: 174a79ff9515 ("bpf: sockmap with sk redirect support")
>> Reported-by: Alexei Starovoitov <ast@kernel.org>
>> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
>> ---
>>  kernel/bpf/sockmap.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
>> index f7e5e6c..39de541 100644
>> --- a/kernel/bpf/sockmap.c
>> +++ b/kernel/bpf/sockmap.c
>> @@ -135,7 +135,8 @@ static void smap_do_verdict(struct smap_psock *psock, struct sk_buff *skb)
>>  	/* Fall through and free skb otherwise */
>>  	case SK_DROP:
>>  	default:
>> -		preempt_enable();
>> +		if (rc != SK_REDIRECT)
>> +			preempt_enable();
>>  		kfree_skb(skb);
>>  	}
>>  }
>>
>
> Yep looks good, nice catch Alexei. Thanks! I'll add a selftests entry
> in test_maps to catch this fall through case. Looks like we don't hit
> this case during selftests at the moment.
>
> Acked-by: John Fastabend <john.fastabend@gmail.com>
>

Acked-by: Alexei Starovoitov <ast@kernel.org>

[PATCH net-next 2/2] bpf: reuse tc bpf prologue for sk skb progs

[Daniel Borkmann]

Given both program types are effecitvely doing the same in the
prologue, just reuse the one that we had for tc and only adapt
to the corresponding drop verdict value. That way, we don't need
to have the duplicate from 8a31db561566 ("bpf: add access to sock
fields and pkt data from sk_skb programs") to maintain.

Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
---
 net/core/filter.c | 47 ++++++++++-------------------------------------
 1 file changed, 10 insertions(+), 37 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index e9f8dce..9865a98 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3456,8 +3456,8 @@ static bool sock_filter_is_valid_access(int off, int size,
 	return true;
 }
 
-static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
-			       const struct bpf_prog *prog)
+static int bpf_unclone_prologue(struct bpf_insn *insn_buf, bool direct_write,
+				const struct bpf_prog *prog, int drop_verdict)
 {
 	struct bpf_insn *insn = insn_buf;
 
@@ -3484,7 +3484,7 @@ static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
 	 * return TC_ACT_SHOT;
 	 */
 	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2);
-	*insn++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_0, TC_ACT_SHOT);
+	*insn++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_0, drop_verdict);
 	*insn++ = BPF_EXIT_INSN();
 
 	/* restore: */
@@ -3495,6 +3495,12 @@ static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
 	return insn - insn_buf;
 }
 
+static int tc_cls_act_prologue(struct bpf_insn *insn_buf, bool direct_write,
+			       const struct bpf_prog *prog)
+{
+	return bpf_unclone_prologue(insn_buf, direct_write, prog, TC_ACT_SHOT);
+}
+
 static bool tc_cls_act_is_valid_access(int off, int size,
 				       enum bpf_access_type type,
 				       struct bpf_insn_access_aux *info)
@@ -3601,40 +3607,7 @@ static bool sock_ops_is_valid_access(int off, int size,
 static int sk_skb_prologue(struct bpf_insn *insn_buf, bool direct_write,
 			   const struct bpf_prog *prog)
 {
-	struct bpf_insn *insn = insn_buf;
-
-	if (!direct_write)
-		return 0;
-
-	/* if (!skb->cloned)
-	 *       goto start;
-	 *
-	 * (Fast-path, otherwise approximation that we might be
-	 *  a clone, do the rest in helper.)
-	 */
-	*insn++ = BPF_LDX_MEM(BPF_B, BPF_REG_6, BPF_REG_1, CLONED_OFFSET());
-	*insn++ = BPF_ALU32_IMM(BPF_AND, BPF_REG_6, CLONED_MASK);
-	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_6, 0, 7);
-
-	/* ret = bpf_skb_pull_data(skb, 0); */
-	*insn++ = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
-	*insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_2, BPF_REG_2);
-	*insn++ = BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
-			       BPF_FUNC_skb_pull_data);
-	/* if (!ret)
-	 *      goto restore;
-	 * return SK_DROP;
-	 */
-	*insn++ = BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2);
-	*insn++ = BPF_ALU32_IMM(BPF_MOV, BPF_REG_0, SK_DROP);
-	*insn++ = BPF_EXIT_INSN();
-
-	/* restore: */
-	*insn++ = BPF_MOV64_REG(BPF_REG_1, BPF_REG_6);
-	/* start: */
-	*insn++ = prog->insnsi[0];
-
-	return insn - insn_buf;
+	return bpf_unclone_prologue(insn_buf, direct_write, prog, SK_DROP);
 }
 
 static bool sk_skb_is_valid_access(int off, int size,
-- 
1.9.3

Re: [PATCH net-next 2/2] bpf: reuse tc bpf prologue for sk skb progs

[John Fastabend]

On 08/17/2017 08:22 AM, Daniel Borkmann wrote:
> Given both program types are effecitvely doing the same in the
> prologue, just reuse the one that we had for tc and only adapt
> to the corresponding drop verdict value. That way, we don't need
> to have the duplicate from 8a31db561566 ("bpf: add access to sock
> fields and pkt data from sk_skb programs") to maintain.
> 
> Reported-by: Alexei Starovoitov <ast@kernel.org>
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> ---
>  net/core/filter.c | 47 ++++++++++-------------------------------------
>  1 file changed, 10 insertions(+), 37 deletions(-)
> 

Nice clean-up, Thanks.

Acked-by: John Fastabend <john.fastabend@gmail.com>

Re: [PATCH net-next 2/2] bpf: reuse tc bpf prologue for sk skb progs

[Alexei Starovoitov]

On 8/17/17 9:05 AM, John Fastabend wrote:
> On 08/17/2017 08:22 AM, Daniel Borkmann wrote:
>> Given both program types are effecitvely doing the same in the
>> prologue, just reuse the one that we had for tc and only adapt
>> to the corresponding drop verdict value. That way, we don't need
>> to have the duplicate from 8a31db561566 ("bpf: add access to sock
>> fields and pkt data from sk_skb programs") to maintain.
>>
>> Reported-by: Alexei Starovoitov <ast@kernel.org>
>> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
>> ---
>>  net/core/filter.c | 47 ++++++++++-------------------------------------
>>  1 file changed, 10 insertions(+), 37 deletions(-)
>>
>
> Nice clean-up, Thanks.
>
> Acked-by: John Fastabend <john.fastabend@gmail.com>
>

Acked-by: Alexei Starovoitov <ast@kernel.org>

Re: [PATCH net-next 0/2] Two BPF smap related followups

[David Miller]

From: Daniel Borkmann <daniel@iogearbox.net>
Date: Thu, 17 Aug 2017 17:22:35 +0200

> Fixing preemption imbalance and consolidating prologue
> generation. Thanks!

Series applied, thanks.