From: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Date: Tue, 9 Oct 2018 10:04:49 +0900
Subject: bpf: error handling when map_lookup_elem isn't supported
Patch-mainline: v4.20-rc1
Git-commit: 509db2833e0ddac7faf6e7d2dd6e7f85c98fbee0
References: bsc#1109837

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>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 kernel/bpf/syscall.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -671,10 +671,15 @@ static int map_lookup_elem(union bpf_att
 	} 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)