netdev - [PATCH bpf-next 5/8] bpf: offload: free program id when device disappears

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Date:   Tue, 19 Dec 2017 20:10:03 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     netdev@...r.kernel.org, alexei.starovoitov@...il.com,
        daniel@...earbox.net
Cc:     ktkhai@...tuozzo.com, oss-drivers@...ronome.com,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: [PATCH bpf-next 5/8] bpf: offload: free program id when device disappears

Bound programs are quite useless after their device disappears.
They are simply waiting for reference count to go to zero,
don't list them in BPF_PROG_GET_NEXT_ID by freeing their ID
early.

Note that orphaned offload programs will return -ENODEV on
BPF_OBJ_GET_INFO_BY_FD so user will never see ID 0.

Signed-off-by: Jakub Kicinski <jakub.kicinski@...ronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@...ronome.com>
Acked-by: Alexei Starovoitov <ast@...nel.org>
---
 include/linux/bpf.h  | 2 ++
 kernel/bpf/offload.c | 3 +++
 kernel/bpf/syscall.c | 9 +++++++--
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 669549f7e3e8..9a916ab34299 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -357,6 +357,8 @@ void bpf_prog_put(struct bpf_prog *prog);
 int __bpf_prog_charge(struct user_struct *user, u32 pages);
 void __bpf_prog_uncharge(struct user_struct *user, u32 pages);
 
+void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock);
+
 struct bpf_map *bpf_map_get_with_uref(u32 ufd);
 struct bpf_map *__bpf_map_get(struct fd f);
 struct bpf_map * __must_check bpf_map_inc(struct bpf_map *map, bool uref);
diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
index 9988dc4038e6..1af94cb4f815 100644
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -128,6 +128,9 @@ static void __bpf_prog_offload_destroy(struct bpf_prog *prog)
 	if (offload->dev_state)
 		WARN_ON(__bpf_offload_ndo(prog, BPF_OFFLOAD_DESTROY, &data));
 
+	/* Make sure BPF_PROG_GET_NEXT_ID can't find this dead program */
+	bpf_prog_free_id(prog, true);
+
 	list_del_init(&offload->offloads);
 	kfree(offload);
 	prog->aux->offload = NULL;
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 1143db61584c..7d9f5b0f0e49 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -905,9 +905,13 @@ static int bpf_prog_alloc_id(struct bpf_prog *prog)
 	return id > 0 ? 0 : id;
 }
 
-static void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)
+void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)
 {
-	/* cBPF to eBPF migrations are currently not in the idr store. */
+	/* cBPF to eBPF migrations are currently not in the idr store.
+	 * Offloaded programs are removed from the store when their device
+	 * disappears - even if someone grabs an fd to them they are unusable,
+	 * simply waiting for refcnt to drop to be freed.
+	 */
 	if (!prog->aux->id)
 		return;
 
@@ -917,6 +921,7 @@ static void bpf_prog_free_id(struct bpf_prog *prog, bool do_idr_lock)
 		__acquire(&prog_idr_lock);
 
 	idr_remove(&prog_idr, prog->aux->id);
+	prog->aux->id = 0;
 
 	if (do_idr_lock)
 		spin_unlock_bh(&prog_idr_lock);
-- 
2.15.1