net/handshake: hand off the pinned file reference to accept_doit

handshake_req_next() removes the request from the per-net
pending list and drops hn_lock before handshake_nl_accept_doit()
reads req->hr_sk->sk_socket and dereferences sock->file (once in
FD_PREPARE() and again in get_file()).  In that window a
consumer running tls_handshake_cancel() followed by sockfd_put()
(svc_sock_free) or __fput_sync() (xs_reset_transport) releases
sock->file.  sock_release() then runs sock_orphan(), zeroing
sk_socket, and frees the struct socket.  The accept-side code
either reads NULL through sk_socket or chases freed memory.

The submit-side sock_hold() does not prevent this.  sk_refcnt
protects struct sock, but struct socket and sock->file are
independently refcounted via the file descriptor the consumer
owns.  Pinning sk leaves sock and sock->file unprotected.

Retarget the accept-side dereferences at req->hr_file, which was
pinned at submit time, instead of req->hr_sk->sk_socket->file.
Pinning on its own is not sufficient: a consumer that cancels
between handshake_req_next() returning and accept_doit reaching
FD_PREPARE() takes the !remove_pending() branch in
handshake_req_cancel() and drops hr_file before the accept side
takes its own reference.  Hand off an additional file reference
inside handshake_req_next(), under hn_lock, so the accept side
operates on a reference that no concurrent handshake_req_cancel()
can revoke.  FD_PREPARE() consumes that handed-off reference,
either by transferring it to the new fd in fd_publish() or by
dropping it in the cleanup destructor on error; the explicit
get_file() that previously balanced FD_PREPARE() is therefore
redundant and goes away.

Update handshake_req_cancel_test2 and _test3 to simulate the
FD_PREPARE() consumption with an fput() so the kunit file-count
assertions stay balanced.

Reported-by: Chris Mason <clm@meta.com>
Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Link: https://patch.msgid.link/20260525-handshake-file-pin-v3-5-66c616906ead@oracle.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/handshake/handshake-test.c b/net/handshake/handshake-test.c
index df3948e807a0fd691fff71ec26f5dab7521a8c57..9cc7a95f41207ea5e074edde74ffc38de395ea49 100644 (file)
--- a/net/handshake/handshake-test.c
+++ b/net/handshake/handshake-test.c
@@ -375,6 +375,10 @@ static void handshake_req_cancel_test2(struct kunit *test)
        /* Pretend to accept this request */
        next = handshake_req_next(hn, HANDSHAKE_HANDLER_CLASS_TLSHD);
        KUNIT_ASSERT_PTR_EQ(test, req, next);
+       /* Simulate FD_PREPARE() consuming the file reference handed
+        * off by handshake_req_next(); see handshake_nl_accept_doit().
+        */
+       fput(filp);
 
        /* Act */
        result = handshake_req_cancel(sock->sk);
@@ -417,6 +421,10 @@ static void handshake_req_cancel_test3(struct kunit *test)
        /* Pretend to accept this request */
        next = handshake_req_next(hn, HANDSHAKE_HANDLER_CLASS_TLSHD);
        KUNIT_ASSERT_PTR_EQ(test, req, next);
+       /* Simulate FD_PREPARE() consuming the file reference handed
+        * off by handshake_req_next(); see handshake_nl_accept_doit().
+        */
+       fput(filp);
 
        /* Pretend to complete this request */
        handshake_complete(next, -ETIMEDOUT, NULL);

diff --git a/net/handshake/netlink.c b/net/handshake/netlink.c
index 1a5821eb7184708c25ebaf7aa888b473aa630271..21d6cbd52fcdb603b0322507d65fbd1b60b947f7 100644 (file)
--- a/net/handshake/netlink.c
+++ b/net/handshake/netlink.c
@@ -92,7 +92,6 @@ int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info)
        struct net *net = sock_net(skb->sk);
        struct handshake_net *hn = handshake_pernet(net);
        struct handshake_req *req = NULL;
-       struct socket *sock;
        int class, err;
 
        err = -EOPNOTSUPP;
@@ -107,15 +106,13 @@ int handshake_nl_accept_doit(struct sk_buff *skb, struct genl_info *info)
        err = -EAGAIN;
        req = handshake_req_next(hn, class);
        if (req) {
-               sock = req->hr_sk->sk_socket;
-
-               FD_PREPARE(fdf, O_CLOEXEC, sock->file);
+               FD_PREPARE(fdf, O_CLOEXEC, req->hr_file);
                if (fdf.err) {
+                       fput(req->hr_file); /* drop ref from handshake_req_next() */
                        err = fdf.err;
                        goto out_complete;
                }
 
-               get_file(sock->file); /* FD_PREPARE() consumes a reference. */
                err = req->hr_proto->hp_accept(req, info, fd_prepare_fd(fdf));
                if (err)
                        goto out_complete; /* Automatic cleanup handles fput */

diff --git a/net/handshake/request.c b/net/handshake/request.c
index da064511ab86006c0ce9307fa2873c2f95e7b120..e2d7ee7ce6e0e025592e243fddfc24f5180cddcf 100644 (file)
--- a/net/handshake/request.c
+++ b/net/handshake/request.c
@@ -178,6 +178,17 @@ static bool remove_pending(struct handshake_net *hn, struct handshake_req *req)
        return ret;
 }
 
+/**
+ * handshake_req_next - Return the next queued handshake request
+ * @hn: per-net handshake state
+ * @class: handler class to match
+ *
+ * On a non-NULL return, the caller owns an extra reference
+ * on @req->hr_file.  FD_PREPARE() consumes it on success; on
+ * the FD_PREPARE() failure path the caller must fput() it.
+ *
+ * Return: pointer to a removed handshake_req, or NULL.
+ */
 struct handshake_req *handshake_req_next(struct handshake_net *hn, int class)
 {
        struct handshake_req *req, *pos;
@@ -188,6 +199,13 @@ struct handshake_req *handshake_req_next(struct handshake_net *hn, int class)
                if (pos->hr_proto->hp_handler_class != class)
                        continue;
                __remove_pending_locked(hn, pos);
+               /* Hand off a file reference to the accept side under
+                * hn_lock.  A concurrent handshake_req_cancel() can drop
+                * hr_file before accept reaches FD_PREPARE(); this extra
+                * reference keeps the file alive until FD_PREPARE() takes
+                * ownership.
+                */
+               get_file(pos->hr_file);
                req = pos;
                break;
        }