bpf: error handling when map_lookup_elem isn't supported

The error value returned by map_lookup_elem doesn't differentiate
whether lookup was failed because of invalid key or lookup is not
supported.

Lets add handling for -EOPNOTSUPP return value of map_lookup_elem()
method of map, with expectation from map's implementation that it
should return -EOPNOTSUPP if lookup is not supported.

The errno for bpf syscall for BPF_MAP_LOOKUP_ELEM command will be set
to EOPNOTSUPP if map lookup is not supported.

Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 5742df21598c..4f416234251f 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -719,10 +719,15 @@ static int map_lookup_elem(union bpf_attr *attr)
         } else {
                 rcu_read_lock();
                 ptr = map->ops->map_lookup_elem(map, key);
-                if (ptr)
+                if (IS_ERR(ptr)) {
+                        err = PTR_ERR(ptr);
+                } else if (!ptr) {
+                        err = -ENOENT;
+                } else {
+                        err = 0;
                         memcpy(value, ptr, value_size);
+                }
                 rcu_read_unlock();
-                err = ptr ? 0 : -ENOENT;
         }
 
         if (err)