[PATCH bpf] bpf: Fix error usage of map_fd and fdget() in generic_map_update_batch()

[Xu Kuohai <xukuohai@xxxxxxxxxx>]

1. The ufd in generic_map_update_batch() should be read from batch.map_fd;
2. A call to fdget() should be followed by a symmetric call to fdput().

Fixes: aa2e93b8e58e ("bpf: Add generic support for update and delete batch ops")
Signed-off-by: Xu Kuohai <xukuohai@xxxxxxxxxx>
---
 kernel/bpf/syscall.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 4e50c0bfdb7d..9dab49d3f394 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1337,12 +1337,11 @@ int generic_map_update_batch(struct bpf_map *map,
 	void __user *values = u64_to_user_ptr(attr->batch.values);
 	void __user *keys = u64_to_user_ptr(attr->batch.keys);
 	u32 value_size, cp, max_count;
-	int ufd = attr->map_fd;
+	int ufd = attr->batch.map_fd;
 	void *key, *value;
 	struct fd f;
 	int err = 0;
 
-	f = fdget(ufd);
 	if (attr->batch.elem_flags & ~BPF_F_LOCK)
 		return -EINVAL;
 
@@ -1367,6 +1366,7 @@ int generic_map_update_batch(struct bpf_map *map,
 		return -ENOMEM;
 	}
 
+	f = fdget(ufd); /* bpf_map_do_batch() guarantees ufd is valid */
 	for (cp = 0; cp < max_count; cp++) {
 		err = -EFAULT;
 		if (copy_from_user(key, keys + cp * map->key_size,
@@ -1386,6 +1386,7 @@ int generic_map_update_batch(struct bpf_map *map,
 
 	kvfree(value);
 	kvfree(key);
+	fdput(f);
 	return err;
 }
 
-- 
2.27.0