[PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[Pedro Tammela]

The current code only checks flags in 'bpf_ringbuf_output()'.

Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
---
 include/uapi/linux/bpf.h       |  8 ++++----
 kernel/bpf/ringbuf.c           | 13 +++++++++++--
 tools/include/uapi/linux/bpf.h |  8 ++++----
 3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 100cb2e4c104..38b0b15f99f0 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -4073,7 +4073,7 @@ union bpf_attr {
  * 		Valid pointer with *size* bytes of memory available; NULL,
  * 		otherwise.
  *
- * void bpf_ringbuf_submit(void *data, u64 flags)
+ * long bpf_ringbuf_submit(void *data, u64 flags)
  * 	Description
  * 		Submit reserved ring buffer sample, pointed to by *data*.
  * 		If **BPF_RB_NO_WAKEUP** is specified in *flags*, no notification
@@ -4083,9 +4083,9 @@ union bpf_attr {
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
  * 	Return
- * 		Nothing. Always succeeds.
+ * 		0 on success, or a negative error in case of failure.
  *
- * void bpf_ringbuf_discard(void *data, u64 flags)
+ * long bpf_ringbuf_discard(void *data, u64 flags)
  * 	Description
  * 		Discard reserved ring buffer sample, pointed to by *data*.
  * 		If **BPF_RB_NO_WAKEUP** is specified in *flags*, no notification
@@ -4095,7 +4095,7 @@ union bpf_attr {
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
  * 	Return
- * 		Nothing. Always succeeds.
+ * 		0 on success, or a negative error in case of failure.
  *
  * u64 bpf_ringbuf_query(void *ringbuf, u64 flags)
  *	Description
diff --git a/kernel/bpf/ringbuf.c b/kernel/bpf/ringbuf.c
index f25b719ac786..f76dafe2427e 100644
--- a/kernel/bpf/ringbuf.c
+++ b/kernel/bpf/ringbuf.c
@@ -397,26 +397,35 @@ static void bpf_ringbuf_commit(void *sample, u64 flags, bool discard)
 
 BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
 {
+	if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
+		return -EINVAL;
+
 	bpf_ringbuf_commit(sample, flags, false /* discard */);
+
 	return 0;
 }
 
 const struct bpf_func_proto bpf_ringbuf_submit_proto = {
 	.func		= bpf_ringbuf_submit,
-	.ret_type	= RET_VOID,
+	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_ALLOC_MEM,
 	.arg2_type	= ARG_ANYTHING,
 };
 
 BPF_CALL_2(bpf_ringbuf_discard, void *, sample, u64, flags)
 {
+
+	if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
+		return -EINVAL;
+
 	bpf_ringbuf_commit(sample, flags, true /* discard */);
+
 	return 0;
 }
 
 const struct bpf_func_proto bpf_ringbuf_discard_proto = {
 	.func		= bpf_ringbuf_discard,
-	.ret_type	= RET_VOID,
+	.ret_type	= RET_INTEGER,
 	.arg1_type	= ARG_PTR_TO_ALLOC_MEM,
 	.arg2_type	= ARG_ANYTHING,
 };
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 3d6d324184c0..a32eefb786f9 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -4073,7 +4073,7 @@ union bpf_attr {
  * 		Valid pointer with *size* bytes of memory available; NULL,
  * 		otherwise.
  *
- * void bpf_ringbuf_submit(void *data, u64 flags)
+ * long bpf_ringbuf_submit(void *data, u64 flags)
  * 	Description
  * 		Submit reserved ring buffer sample, pointed to by *data*.
  * 		If **BPF_RB_NO_WAKEUP** is specified in *flags*, no notification
@@ -4083,9 +4083,9 @@ union bpf_attr {
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
  * 	Return
- * 		Nothing. Always succeeds.
+ * 		0 on success, or a negative error in case of failure.
  *
- * void bpf_ringbuf_discard(void *data, u64 flags)
+ * long bpf_ringbuf_discard(void *data, u64 flags)
  * 	Description
  * 		Discard reserved ring buffer sample, pointed to by *data*.
  * 		If **BPF_RB_NO_WAKEUP** is specified in *flags*, no notification
@@ -4095,7 +4095,7 @@ union bpf_attr {
  * 		If **BPF_RB_FORCE_WAKEUP** is specified in *flags*, notification
  * 		of new data availability is sent unconditionally.
  * 	Return
- * 		Nothing. Always succeeds.
+ * 		0 on success, or a negative error in case of failure.
  *
  * u64 bpf_ringbuf_query(void *ringbuf, u64 flags)
  *	Description
-- 
2.25.1

Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[Song Liu]

> On Mar 30, 2021, at 3:37 PM, Pedro Tammela <pctammela@gmail.com> wrote:
> 
> The current code only checks flags in 'bpf_ringbuf_output()'.
> 
> Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>

Acked-by: Song Liu <songliubraving@fb.com>

Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[Alexei Starovoitov]

On Tue, Mar 30, 2021 at 3:54 PM Pedro Tammela <pctammela@gmail.com> wrote:
>
>  BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
>  {
> +       if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
> +               return -EINVAL;
> +
>         bpf_ringbuf_commit(sample, flags, false /* discard */);
> +
>         return 0;

I think ringbuf design was meant for bpf_ringbuf_submit to never fail.
If we do flag validation it probably should be done at the verifier time.

Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[Andrii Nakryiko]

On Tue, Mar 30, 2021 at 4:16 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Tue, Mar 30, 2021 at 3:54 PM Pedro Tammela <pctammela@gmail.com> wrote:
> >
> >  BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
> >  {
> > +       if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
> > +               return -EINVAL;
> > +
> >         bpf_ringbuf_commit(sample, flags, false /* discard */);
> > +
> >         return 0;
>
> I think ringbuf design was meant for bpf_ringbuf_submit to never fail.
> If we do flag validation it probably should be done at the verifier time.

Oops, replied on another version already. But yes, BPF verifier relies
on it succeeding. I don't think we can do flags validation at BPF
verification time, though, because it is defined as non-const integer
and we do have valid cases where we dynamically determine whether to
FORCE_WAKEUP or NO_WAKEUP, based on application-driven criteria (e.g.,
amount of enqueued data).

Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[Pedro Tammela]

Em qua., 31 de mar. de 2021 às 04:02, Andrii Nakryiko
<andrii.nakryiko@gmail.com> escreveu:
>
> On Tue, Mar 30, 2021 at 4:16 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Tue, Mar 30, 2021 at 3:54 PM Pedro Tammela <pctammela@gmail.com> wrote:
> > >
> > >  BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
> > >  {
> > > +       if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
> > > +               return -EINVAL;
> > > +
> > >         bpf_ringbuf_commit(sample, flags, false /* discard */);
> > > +
> > >         return 0;
> >
> > I think ringbuf design was meant for bpf_ringbuf_submit to never fail.
> > If we do flag validation it probably should be done at the verifier time.
>
> Oops, replied on another version already. But yes, BPF verifier relies
> on it succeeding. I don't think we can do flags validation at BPF
> verification time, though, because it is defined as non-const integer
> and we do have valid cases where we dynamically determine whether to
> FORCE_WAKEUP or NO_WAKEUP, based on application-driven criteria (e.g.,
> amount of enqueued data).

Then shouldn't we remove the flags check in 'bpf_ringbuf_output()'?

Re: [PATCH bpf-next v2] bpf: check flags in 'bpf_ringbuf_discard()' and 'bpf_ringbuf_submit()'

[Andrii Nakryiko]

On Sat, Apr 3, 2021 at 6:29 AM Pedro Tammela <pctammela@gmail.com> wrote:
>
> Em qua., 31 de mar. de 2021 às 04:02, Andrii Nakryiko
> <andrii.nakryiko@gmail.com> escreveu:
> >
> > On Tue, Mar 30, 2021 at 4:16 PM Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > On Tue, Mar 30, 2021 at 3:54 PM Pedro Tammela <pctammela@gmail.com> wrote:
> > > >
> > > >  BPF_CALL_2(bpf_ringbuf_submit, void *, sample, u64, flags)
> > > >  {
> > > > +       if (unlikely(flags & ~(BPF_RB_NO_WAKEUP | BPF_RB_FORCE_WAKEUP)))
> > > > +               return -EINVAL;
> > > > +
> > > >         bpf_ringbuf_commit(sample, flags, false /* discard */);
> > > > +
> > > >         return 0;
> > >
> > > I think ringbuf design was meant for bpf_ringbuf_submit to never fail.
> > > If we do flag validation it probably should be done at the verifier time.
> >
> > Oops, replied on another version already. But yes, BPF verifier relies
> > on it succeeding. I don't think we can do flags validation at BPF
> > verification time, though, because it is defined as non-const integer
> > and we do have valid cases where we dynamically determine whether to
> > FORCE_WAKEUP or NO_WAKEUP, based on application-driven criteria (e.g.,
> > amount of enqueued data).
>
> Then shouldn't we remove the flags check in 'bpf_ringbuf_output()'?

bpf_ringbuf_output() combines reserve + commit operations, so if it
performs checks before anything is reserved in ringbuf, it's ok for it
to fail and return error. So I don't see any problem there. But once
it internally reserves, it always proceeds to complete the commit.