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

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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: 3b3009ea8a ("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>
This commit is contained in:
Chuck Lever 2026-05-25 12:51:19 -04:00 committed by Paolo Abeni
parent 09dba37eee
commit f4251190e5
3 changed files with 28 additions and 5 deletions
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8
net/handshake/handshake-test.c
View File

@ -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);

7
net/handshake/netlink.c
View File

@ -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 */

18
net/handshake/request.c
View File

@ -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;
}