net: fix out-of-bounds access in ops_init

commit a26ff37e624d12e28077e5b24d2b264f62764ad6 upstream.

net_alloc_generic is called by net_alloc, which is called without any
locking. It reads max_gen_ptrs, which is changed under pernet_ops_rwsem. It
is read twice, first to allocate an array, then to set s.len, which is
later used to limit the bounds of the array access.

It is possible that the array is allocated and another thread is
registering a new pernet ops, increments max_gen_ptrs, which is then used
to set s.len with a larger than allocated length for the variable array.

Fix it by reading max_gen_ptrs only once in net_alloc_generic. If
max_gen_ptrs is later incremented, it will be caught in net_assign_generic.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Fixes: 073862ba5d24 ("netns: fix net_alloc_generic()")
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20240502132006.3430840-1-cascardo@igalia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 72799533426b6162256d7c4eef355af96c66e844..b36444e3810c260439aa1b84dc0ceb3e88d4d4b6 100644 (file)
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -69,12 +69,15 @@ DEFINE_COOKIE(net_cookie);
 
 static struct net_generic *net_alloc_generic(void)
 {
+       unsigned int gen_ptrs = READ_ONCE(max_gen_ptrs);
+       unsigned int generic_size;
        struct net_generic *ng;
-       unsigned int generic_size = offsetof(struct net_generic, ptr[max_gen_ptrs]);
+
+       generic_size = offsetof(struct net_generic, ptr[gen_ptrs]);
 
        ng = kzalloc(generic_size, GFP_KERNEL);
        if (ng)
-               ng->s.len = max_gen_ptrs;
+               ng->s.len = gen_ptrs;
 
        return ng;
 }
@@ -1278,7 +1281,11 @@ static int register_pernet_operations(struct list_head *list,
                if (error < 0)
                        return error;
                *ops->id = error;
-               max_gen_ptrs = max(max_gen_ptrs, *ops->id + 1);
+               /* This does not require READ_ONCE as writers already hold
+                * pernet_ops_rwsem. But WRITE_ONCE is needed to protect
+                * net_alloc_generic.
+                */
+               WRITE_ONCE(max_gen_ptrs, max(max_gen_ptrs, *ops->id + 1));
        }
        error = __register_pernet_operations(list, ops);
        if (error) {