[PATCH bpf] bpf: fix XDP FD-based attach/detach logic around XDP_FLAGS_UPDATE_IF_NOEXIST

[PATCH bpf] bpf: fix XDP FD-based attach/detach logic around XDP_FLAGS_UPDATE_IF_NOEXIST

[Andrii Nakryiko]

Enforce XDP_FLAGS_UPDATE_IF_NOEXIST only if new BPF program to be attached is
non-NULL (i.e., we are not detaching a BPF program).

Reported-by: Stanislav Fomichev <sdf@google.com>
Fixes: d4baa9368a5e ("bpf, xdp: Extract common XDP program attachment logic")
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
---
 net/core/dev.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 7df6c9617321..b5d1129d8310 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -8913,10 +8913,6 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
 		NL_SET_ERR_MSG(extack, "Active program does not match expected");
 		return -EEXIST;
 	}
-	if ((flags & XDP_FLAGS_UPDATE_IF_NOEXIST) && cur_prog) {
-		NL_SET_ERR_MSG(extack, "XDP program already attached");
-		return -EBUSY;
-	}
 
 	/* put effective new program into new_prog */
 	if (link)
@@ -8927,6 +8923,10 @@ static int dev_xdp_attach(struct net_device *dev, struct netlink_ext_ack *extack
 		enum bpf_xdp_mode other_mode = mode == XDP_MODE_SKB
 					       ? XDP_MODE_DRV : XDP_MODE_SKB;
 
+		if ((flags & XDP_FLAGS_UPDATE_IF_NOEXIST) && cur_prog) {
+			NL_SET_ERR_MSG(extack, "XDP program already attached");
+			return -EBUSY;
+		}
 		if (!offload && dev_xdp_prog(dev, other_mode)) {
 			NL_SET_ERR_MSG(extack, "Native and generic XDP can't be active at the same time");
 			return -EEXIST;
-- 
2.24.1

Re: [PATCH bpf] bpf: fix XDP FD-based attach/detach logic around XDP_FLAGS_UPDATE_IF_NOEXIST

[Toke Høiland-Jørgensen]

Andrii Nakryiko <andriin@fb.com> writes:

> Enforce XDP_FLAGS_UPDATE_IF_NOEXIST only if new BPF program to be attached is
> non-NULL (i.e., we are not detaching a BPF program).
>
> Reported-by: Stanislav Fomichev <sdf@google.com>
> Fixes: d4baa9368a5e ("bpf, xdp: Extract common XDP program attachment logic")
> Signed-off-by: Andrii Nakryiko <andriin@fb.com>

Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>

Re: [PATCH bpf] bpf: fix XDP FD-based attach/detach logic around XDP_FLAGS_UPDATE_IF_NOEXIST

[Stanislav Fomichev]

On Wed, Aug 12, 2020 at 2:24 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
>
> Andrii Nakryiko <andriin@fb.com> writes:
>
> > Enforce XDP_FLAGS_UPDATE_IF_NOEXIST only if new BPF program to be attached is
> > non-NULL (i.e., we are not detaching a BPF program).
> >
> > Reported-by: Stanislav Fomichev <sdf@google.com>
> > Fixes: d4baa9368a5e ("bpf, xdp: Extract common XDP program attachment logic")
> > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
>
> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
That fixed it for me, thank you!

Tested-by: Stanislav Fomichev <sdf@google.com>

Re: [PATCH bpf] bpf: fix XDP FD-based attach/detach logic around XDP_FLAGS_UPDATE_IF_NOEXIST

[Alexei Starovoitov]

On Wed, Aug 12, 2020 at 8:48 AM Stanislav Fomichev <sdf@google.com> wrote:
>
> On Wed, Aug 12, 2020 at 2:24 AM Toke Høiland-Jørgensen <toke@redhat.com> wrote:
> >
> > Andrii Nakryiko <andriin@fb.com> writes:
> >
> > > Enforce XDP_FLAGS_UPDATE_IF_NOEXIST only if new BPF program to be attached is
> > > non-NULL (i.e., we are not detaching a BPF program).
> > >
> > > Reported-by: Stanislav Fomichev <sdf@google.com>
> > > Fixes: d4baa9368a5e ("bpf, xdp: Extract common XDP program attachment logic")
> > > Signed-off-by: Andrii Nakryiko <andriin@fb.com>
> >
> > Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
> That fixed it for me, thank you!
>
> Tested-by: Stanislav Fomichev <sdf@google.com>

Applied. Thanks