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svcrdma: Release transport resources synchronously

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NFSD has always supported added network listeners. The new netlink
protocol now enables the removal of listeners.

Olga noticed that if an RDMA listener is removed and immediately
re-added, the deferred __svc_rdma_free() function might not have
run yet, so some or all of the old listener's RDMA resources
linger, which prevents a new listener on the same address from
being created.

Also, svc_xprt_free() does a module_put() just after calling
->xpo_free(). That means if there is deferred work going on, the
module could be unloaded before that work is even started,
resulting in a UAF.

Neil asks:
> What particular part of __svc_rdma_free() needs to run in order for a
> subsequent registration to succeed?
> Can that bit be run directory from svc_rdma_free() rather than be
> delayed?
> (I know almost nothing about rdma so forgive me if the answers to these
> questions seems obvious)

The reasons I can recall are:

 - Some of the transport tear-down work can sleep
 - Releasing a cm_id is tricky and can deadlock

We might be able to mitigate the second issue with judicious
application of transport reference counting.

Reported-by: Olga Kornievskaia <okorniev@redhat.com>
Closes: https://lore.kernel.org/linux-nfs/20250821204328.89218-1-okorniev@redhat.com/
Suggested-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
This commit is contained in:
Chuck Lever
2025-09-03 11:53:35 -04:00
parent 6a23ae0a96
commit bf94dea7fd
1 changed files with 8 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

19
net/sunrpc/xprtrdma/svc_rdma_transport.c
View File

@@ -591,12 +591,18 @@ static void svc_rdma_detach(struct svc_xprt *xprt)
rdma_disconnect(rdma->sc_cm_id);
}
static void __svc_rdma_free(struct work_struct *work)
/**
* svc_rdma_free - Release class-specific transport resources
* @xprt: Generic svc transport object
*/
static void svc_rdma_free(struct svc_xprt *xprt)
{
struct svcxprt_rdma *rdma =
container_of(work, struct svcxprt_rdma, sc_work);
container_of(xprt, struct svcxprt_rdma, sc_xprt);
struct ib_device *device = rdma->sc_cm_id->device;
might_sleep();
/* This blocks until the Completion Queues are empty */
if (rdma->sc_qp && !IS_ERR(rdma->sc_qp))
ib_drain_qp(rdma->sc_qp);
@@ -629,15 +635,6 @@ static void __svc_rdma_free(struct work_struct *work)
kfree(rdma);
}
static void svc_rdma_free(struct svc_xprt *xprt)
{
struct svcxprt_rdma *rdma =
container_of(xprt, struct svcxprt_rdma, sc_xprt);
INIT_WORK(&rdma->sc_work, __svc_rdma_free);
schedule_work(&rdma->sc_work);
}
static int svc_rdma_has_wspace(struct svc_xprt *xprt)
{
struct svcxprt_rdma *rdma =