Re: [PATCH 1/3] bpf: Don't check for current being NULL

Re: [PATCH 1/3] bpf: Don't check for current being NULL

[Alexei Starovoitov]

On Mon, Oct 16, 2017 at 11:18 AM, Richard Weinberger <richard@nod.at> wrote:
> current is never NULL.
>
> Signed-off-by: Richard Weinberger <richard@nod.at>
> ---
>  kernel/bpf/helpers.c | 12 ------------
>  1 file changed, 12 deletions(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 3d24e238221e..e8845adcd15e 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -120,9 +120,6 @@ BPF_CALL_0(bpf_get_current_pid_tgid)
>  {
>         struct task_struct *task = current;
>
> -       if (unlikely(!task))
> -               return -EINVAL;
> -

really? in all context? including irq and nmi?

Re: [PATCH 1/3] bpf: Don't check for current being NULL

[Richard Weinberger]

Alexei,

Am Dienstag, 17. Oktober 2017, 00:06:08 CEST schrieb Alexei Starovoitov:
> On Mon, Oct 16, 2017 at 11:18 AM, Richard Weinberger <richard@nod.at> wrote:
> > current is never NULL.
> > 
> > Signed-off-by: Richard Weinberger <richard@nod.at>
> > ---
> > 
> >  kernel/bpf/helpers.c | 12 ------------
> >  1 file changed, 12 deletions(-)
> > 
> > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > index 3d24e238221e..e8845adcd15e 100644
> > --- a/kernel/bpf/helpers.c
> > +++ b/kernel/bpf/helpers.c
> > @@ -120,9 +120,6 @@ BPF_CALL_0(bpf_get_current_pid_tgid)
> > 
> >  {
> >  
> >         struct task_struct *task = current;
> > 
> > -       if (unlikely(!task))
> > -               return -EINVAL;
> > -
> 
> really? in all context? including irq and nmi?

I would be astonished current is NULL in such a context.

To be sure, let's CC linux-arch.
IIRC I talked also with Al about this and he also assumed that current
cannot be NULL.

Thanks,
//richard

Re: [PATCH 1/3] bpf: Don't check for current being NULL

[Alexei Starovoitov]

On Tue, Oct 17, 2017 at 12:23:13AM +0200, Richard Weinberger wrote:
> Alexei,
> 
> Am Dienstag, 17. Oktober 2017, 00:06:08 CEST schrieb Alexei Starovoitov:
> > On Mon, Oct 16, 2017 at 11:18 AM, Richard Weinberger <richard@nod.at> wrote:
> > > current is never NULL.
> > > 
> > > Signed-off-by: Richard Weinberger <richard@nod.at>
> > > ---
> > > 
> > >  kernel/bpf/helpers.c | 12 ------------
> > >  1 file changed, 12 deletions(-)
> > > 
> > > diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> > > index 3d24e238221e..e8845adcd15e 100644
> > > --- a/kernel/bpf/helpers.c
> > > +++ b/kernel/bpf/helpers.c
> > > @@ -120,9 +120,6 @@ BPF_CALL_0(bpf_get_current_pid_tgid)
> > > 
> > >  {
> > >  
> > >         struct task_struct *task = current;
> > > 
> > > -       if (unlikely(!task))
> > > -               return -EINVAL;
> > > -
> > 
> > really? in all context? including irq and nmi?
> 
> I would be astonished current is NULL in such a context.
> 
> To be sure, let's CC linux-arch.
> IIRC I talked also with Al about this and he also assumed that current
> cannot be NULL.

Hmm I probably mistakenly stole the !current check from somewhere.
Happy to delete all these checks then.

[PATCH 1/3] bpf: Don't check for current being NULL

[Richard Weinberger]

current is never NULL.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
 kernel/bpf/helpers.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 3d24e238221e..e8845adcd15e 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -120,9 +120,6 @@ BPF_CALL_0(bpf_get_current_pid_tgid)
 {
 	struct task_struct *task = current;
 
-	if (unlikely(!task))
-		return -EINVAL;
-
 	return (u64) task->tgid << 32 | task->pid;
 }
 
@@ -138,9 +135,6 @@ BPF_CALL_0(bpf_get_current_uid_gid)
 	kuid_t uid;
 	kgid_t gid;
 
-	if (unlikely(!task))
-		return -EINVAL;
-
 	current_uid_gid(&uid, &gid);
 	return (u64) from_kgid(&init_user_ns, gid) << 32 |
 		     from_kuid(&init_user_ns, uid);
@@ -156,9 +150,6 @@ BPF_CALL_2(bpf_get_current_comm, char *, buf, u32, size)
 {
 	struct task_struct *task = current;
 
-	if (unlikely(!task))
-		goto err_clear;
-
 	strncpy(buf, task->comm, size);
 
 	/* Verifier guarantees that size > 0. For task->comm exceeding
@@ -167,9 +158,6 @@ BPF_CALL_2(bpf_get_current_comm, char *, buf, u32, size)
 	 */
 	buf[size - 1] = 0;
 	return 0;
-err_clear:
-	memset(buf, 0, size);
-	return -EINVAL;
 }
 
 const struct bpf_func_proto bpf_get_current_comm_proto = {
-- 
2.13.6