[PATCH bpf-next v3 5/9] bpf: offload: free program id when device disappears

[Jakub Kicinski]

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.kicin...@netronome.com>
Reviewed-by: Quentin Monnet <quentin.mon...@netronome.com>
Acked-by: Alexei Starovoitov <a...@kernel.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 3126e1a842e6..e4f1668a021c 100644
--- a/kernel/bpf/offload.c
+++ b/kernel/bpf/offload.c
@@ -130,6 +130,9 @@ 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