[PATCH bpf-next 1/2] bpf: fix setting return values for htab batch ops

[Anton Protopopov]

The map_lookup{,_and_delete}_batch operations are expected to set the
output parameter, counter, to the number of elements successfully copied
to the user space. This is also expected to be true if an error is
returned and the errno is set to a value other than EFAULT. The current
implementation can return -EINVAL without setting the counter to zero, so
some userspace programs may confuse this with a [partially] successful
operation. Move code which sets the counter to zero to the top of the
function so that we always return a correct value.

Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map")
Signed-off-by: Anton Protopopov <aspsk@xxxxxxxxxxxxx>
---
 kernel/bpf/hashtab.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index a8c7e1c5abfa..fa8e3f1e1724 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -1692,6 +1692,13 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 	struct bucket *b;
 	int ret = 0;
 
+	max_count = attr->batch.count;
+	if (!max_count)
+		return 0;
+
+	if (put_user(0, &uattr->batch.count))
+		return -EFAULT;
+
 	elem_map_flags = attr->batch.elem_flags;
 	if ((elem_map_flags & ~BPF_F_LOCK) ||
 	    ((elem_map_flags & BPF_F_LOCK) && !btf_record_has_field(map->record, BPF_SPIN_LOCK)))
@@ -1701,13 +1708,6 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 	if (map_flags)
 		return -EINVAL;
 
-	max_count = attr->batch.count;
-	if (!max_count)
-		return 0;
-
-	if (put_user(0, &uattr->batch.count))
-		return -EFAULT;
-
 	batch = 0;
 	if (ubatch && copy_from_user(&batch, ubatch, sizeof(batch)))
 		return -EFAULT;
-- 
2.34.1