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46bc86c833
The TLS connect path has a use-after-free: nothing pins the
upper rpc_clnt across the delayed connect_worker. xs_connect()
stores task->tk_client in sock_xprt::clnt as a raw pointer
and queues the worker; for TLS-secured transports that worker
is xs_tcp_tls_setup_socket(), which reads several fields out
of the saved pointer (cl_timeout, cl_program, cl_prog,
cl_vers, cl_cred, cl_stats) to construct the args for the
inner handshake rpc_clnt.
The xprt does not reference the rpc_clnt; the rpc_clnt
references the xprt. xs_destroy() does cancel the
connect_worker, but it runs only when the xprt's refcount
drops to zero, which cannot happen until the rpc_clnt
releases its cl_xprt reference in rpc_free_client_work().
When a TLS handshake fails fatally (for example, an mTLS
mount whose client cert does not match the server), the
connecting task is woken with -EACCES and exits, the mount
caller invokes rpc_shutdown_client(), and the upper rpc_clnt
is freed before the queued connect_worker fires.
xs_tcp_tls_setup_socket() then dereferences the freed clnt,
producing the refcount_t underflow Michael Nemanov reported.
Take a reference on the upper rpc_clnt in xs_connect() for
TLS transports via a new rpc_hold_client() helper, and drop
it in the connect_worker's exit path with rpc_release_client().
The xprt_lock_connect() / xprt_unlock_connect() pairing
already serialises xs_connect() with xs_tcp_tls_setup_socket(),
so the take and release are balanced one-for-one.
The non-TLS connect worker (xs_tcp_setup_socket) never reads
sock_xprt::clnt, so leave that path alone and avoid the
clnt-holds-xprt-holds-clnt cycle that would otherwise prevent
xprt destruction.
Reported-by: Michael Nemanov <michael.nemanov@vastdata.com>
Closes: https://lore.kernel.org/linux-nfs/40e3d522-dfcf-4fc1-9c55-b5e81f1536d5@vastdata.com/
Fixes:
|
||
|---|---|---|
| .. | ||
| xdrgen | ||
| addr.h | ||
| auth_gss.h | ||
| auth.h | ||
| bc_xprt.h | ||
| cache.h | ||
| clnt.h | ||
| debug.h | ||
| gss_api.h | ||
| gss_err.h | ||
| gss_krb5.h | ||
| metrics.h | ||
| msg_prot.h | ||
| rdma_rn.h | ||
| rpc_pipe_fs.h | ||
| rpc_rdma_cid.h | ||
| rpc_rdma.h | ||
| sched.h | ||
| stats.h | ||
| svc_rdma_pcl.h | ||
| svc_rdma.h | ||
| svc_xprt.h | ||
| svc.h | ||
| svcauth_gss.h | ||
| svcauth.h | ||
| svcsock.h | ||
| timer.h | ||
| types.h | ||
| xdr.h | ||
| xprt.h | ||
| xprtmultipath.h | ||
| xprtrdma.h | ||
| xprtsock.h | ||