[PATCH bpf] bpf, sockmap: fix sock hash count in alloc_sock_hash_elem

[Daniel Borkmann <daniel@iogearbox.net>]

When we try to allocate a new sock hash entry and the allocation
fails, then sock hash map fails to reduce the map element counter,
meaning we keep accounting this element although it was never used.
Fix it by dropping the element counter on error.

Fixes: 81110384441a ("bpf: sockmap, add hash map support")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
---
 kernel/bpf/sockmap.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 60ceb0e..40c6ef9 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -2269,8 +2269,10 @@ static struct htab_elem *alloc_sock_hash_elem(struct bpf_htab *htab,
 	}
 	l_new = kmalloc_node(htab->elem_size, GFP_ATOMIC | __GFP_NOWARN,
 			     htab->map.numa_node);
-	if (!l_new)
+	if (!l_new) {
+		atomic_dec(&htab->count);
 		return ERR_PTR(-ENOMEM);
+	}
 
 	memcpy(l_new->key, key, key_size);
 	l_new->sk = sk;
-- 
2.9.5