[PATCH net v2 5/7] net/handshake: hand off the pinned file reference to accept_doit
From: Chuck Lever <cel@kernel.org>
Date: 2026-05-21 14:47:36
Also in:
linux-nvme
Subsystem:
handshake upcall for transport layer security, networking [general], the rest · Maintainers:
Chuck Lever, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
From: Chuck Lever <redacted>
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 <redacted>
Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Signed-off-by: Chuck Lever <redacted>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
---
net/handshake/handshake-test.c | 8 ++++++++
net/handshake/netlink.c | 7 ++-----
net/handshake/request.c | 18 ++++++++++++++++++
3 files changed, 28 insertions(+), 5 deletions(-)
diff --git a/net/handshake/handshake-test.c b/net/handshake/handshake-test.c
index df3948e807a0..9cc7a95f4120 100644
--- 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 f395bfc7ff8c..a11041e745da 100644
--- 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 b076ae539422..d24b55af1a0a 100644
--- a/net/handshake/request.c
+++ b/net/handshake/request.c@@ -179,6 +179,17 @@ 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;
@@ -189,6 +200,13 @@ 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; }
--
2.54.0