SUNRPC: Convert rpc_client refcount to use refcount_t

Commit Message

Trond Myklebust July 17, 2021, 5:20 p.m. UTC

From: Trond Myklebust <[e-mail]>

There are now tools in the refcount library that allow us to convert the
client shutdown code.

Reported-by: Xiyu Yang <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>
---
 include/linux/sunrpc/clnt.h          |  3 ++-
 net/sunrpc/auth_gss/gss_rpc_upcall.c |  2 +-
 net/sunrpc/clnt.c                    | 22 ++++++++++------------
 net/sunrpc/debugfs.c                 |  2 +-
 net/sunrpc/rpc_pipe.c                |  2 +-
 5 files changed, 15 insertions(+), 16 deletions(-)

Comments

Benjamin Coddington July 19, 2021, 12:01 p.m. UTC | #1

Hi Trond,

On 17 Jul 2021, at 13:20, [e-mail] wrote:

> @@ -943,7 +941,7 @@ rpc_release_client(struct rpc_clnt *clnt)
>  	do {
>  		if (list_empty(&clnt->cl_tasks))
>  			wake_up(&destroy_wait);
> -		if (!atomic_dec_and_test(&clnt->cl_count))
> +		if (refcount_dec_not_one(&clnt->cl_count))

I guess we're not worried about extra calls racing into rpc_free_auth?

.. hmm, it looks like current code can do that already since we're bumping the
ref up again.  Seems like we could end up in rpcauth_release twice with
an underflow on au_count.

Ben

Trond Myklebust July 19, 2021, 12:07 p.m. UTC | #2

On Mon, 2021-07-19 at 08:01 -0400, Benjamin Coddington wrote:
> Hi Trond,
> 
> On 17 Jul 2021, at 13:20, [e-mail] wrote:
> 
> > @@ -943,7 +941,7 @@ rpc_release_client(struct rpc_clnt *clnt)
> >         do {
> >                 if (list_empty(&clnt->cl_tasks))
> >                         wake_up(&destroy_wait);
> > -               if (!atomic_dec_and_test(&clnt->cl_count))
> > +               if (refcount_dec_not_one(&clnt->cl_count))
> 
> I guess we're not worried about extra calls racing into
> rpc_free_auth?

The refcount would normally be going to zero in the above case. If
anything outside the RPC code itself tries to bump the counter then
that is a very clear cut case of use-after-free.

> 
> .. hmm, it looks like current code can do that already since we're
> bumping the
> ref up again.  Seems like we could end up in rpcauth_release twice
> with
> an underflow on au_count.
> 

As I said, only if there is a use-after-free bug somewhere else.

Benjamin Coddington July 19, 2021, 12:27 p.m. UTC | #3

On 19 Jul 2021, at 8:07, Trond Myklebust wrote:

> On Mon, 2021-07-19 at 08:01 -0400, Benjamin Coddington wrote:
>> Hi Trond,
>>
>> On 17 Jul 2021, at 13:20, [e-mail] wrote:
>>
>>> @@ -943,7 +941,7 @@ rpc_release_client(struct rpc_clnt *clnt)
>>>         do {
>>>                 if (list_empty(&clnt->cl_tasks))
>>>                         wake_up(&destroy_wait);
>>> -               if (!atomic_dec_and_test(&clnt->cl_count))
>>> +               if (refcount_dec_not_one(&clnt->cl_count))
>>
>> I guess we're not worried about extra calls racing into
>> rpc_free_auth?
>
> The refcount would normally be going to zero in the above case. If
> anything outside the RPC code itself tries to bump the counter then
> that is a very clear cut case of use-after-free.

I am thinking about users of rpc_release_client() calling it multiple times,
but perhaps that's not something that happens.  This is a different issue
that's not added by your patch, I was noticing it.

Reviewed-by: Benjamin Coddington <[e-mail]>

Ben

Patch

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index 8b5d5c97553e..b2edd5fc2f0c 100644
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -14,6 +14,7 @@ 
 #include <linux/socket.h>
 #include <linux/in.h>
 #include <linux/in6.h>
+#include <linux/refcount.h>
 
 #include <linux/sunrpc/msg_prot.h>
 #include <linux/sunrpc/sched.h>
@@ -35,7 +36,7 @@  struct rpc_sysfs_client;
  * The high-level client handle
  */
 struct rpc_clnt {
-	atomic_t		cl_count;	/* Number of references */
+	refcount_t		cl_count;	/* Number of references */
 	unsigned int		cl_clid;	/* client id */
 	struct list_head	cl_clients;	/* Global list of clients */
 	struct list_head	cl_tasks;	/* List of tasks */
diff --git a/net/sunrpc/auth_gss/gss_rpc_upcall.c b/net/sunrpc/auth_gss/gss_rpc_upcall.c
index d1c003a25b0f..61c276bddaf2 100644
--- a/net/sunrpc/auth_gss/gss_rpc_upcall.c
+++ b/net/sunrpc/auth_gss/gss_rpc_upcall.c
@@ -160,7 +160,7 @@  static struct rpc_clnt *get_gssp_clnt(struct sunrpc_net *sn)
 	mutex_lock(&sn->gssp_lock);
 	clnt = sn->gssp_clnt;
 	if (clnt)
-		atomic_inc(&clnt->cl_count);
+		refcount_inc(&clnt->cl_count);
 	mutex_unlock(&sn->gssp_lock);
 	return clnt;
 }
diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
index 8b4de70e8ead..9952fc0b1de6 100644
--- a/net/sunrpc/clnt.c
+++ b/net/sunrpc/clnt.c
@@ -167,7 +167,7 @@  static int rpc_clnt_skip_event(struct rpc_clnt *clnt, unsigned long event)
 	case RPC_PIPEFS_MOUNT:
 		if (clnt->cl_pipedir_objects.pdh_dentry != NULL)
 			return 1;
-		if (atomic_read(&clnt->cl_count) == 0)
+		if (refcount_read(&clnt->cl_count) == 0)
 			return 1;
 		break;
 	case RPC_PIPEFS_UMOUNT:
@@ -419,7 +419,7 @@  static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args,
 	clnt->cl_rtt = &clnt->cl_rtt_default;
 	rpc_init_rtt(&clnt->cl_rtt_default, clnt->cl_timeout->to_initval);
 
-	atomic_set(&clnt->cl_count, 1);
+	refcount_set(&clnt->cl_count, 1);
 
 	if (nodename == NULL)
 		nodename = utsname()->nodename;
@@ -431,7 +431,7 @@  static struct rpc_clnt * rpc_new_client(const struct rpc_create_args *args,
 	if (err)
 		goto out_no_path;
 	if (parent)
-		atomic_inc(&parent->cl_count);
+		refcount_inc(&parent->cl_count);
 
 	trace_rpc_clnt_new(clnt, xprt, program->name, args->servername);
 	return clnt;
@@ -918,18 +918,16 @@  rpc_free_client(struct rpc_clnt *clnt)
 static struct rpc_clnt *
 rpc_free_auth(struct rpc_clnt *clnt)
 {
-	if (clnt->cl_auth == NULL)
-		return rpc_free_client(clnt);
-
 	/*
 	 * Note: RPCSEC_GSS may need to send NULL RPC calls in order to
 	 *       release remaining GSS contexts. This mechanism ensures
 	 *       that it can do so safely.
 	 */
-	atomic_inc(&clnt->cl_count);
-	rpcauth_release(clnt->cl_auth);
-	clnt->cl_auth = NULL;
-	if (atomic_dec_and_test(&clnt->cl_count))
+	if (clnt->cl_auth != NULL) {
+		rpcauth_release(clnt->cl_auth);
+		clnt->cl_auth = NULL;
+	}
+	if (refcount_dec_and_test(&clnt->cl_count))
 		return rpc_free_client(clnt);
 	return NULL;
 }
@@ -943,7 +941,7 @@  rpc_release_client(struct rpc_clnt *clnt)
 	do {
 		if (list_empty(&clnt->cl_tasks))
 			wake_up(&destroy_wait);
-		if (!atomic_dec_and_test(&clnt->cl_count))
+		if (refcount_dec_not_one(&clnt->cl_count))
 			break;
 		clnt = rpc_free_auth(clnt);
 	} while (clnt != NULL);
@@ -1082,7 +1080,7 @@  void rpc_task_set_client(struct rpc_task *task, struct rpc_clnt *clnt)
 	if (clnt != NULL) {
 		rpc_task_set_transport(task, clnt);
 		task->tk_client = clnt;
-		atomic_inc(&clnt->cl_count);
+		refcount_inc(&clnt->cl_count);
 		if (clnt->cl_softrtry)
 			task->tk_flags |= RPC_TASK_SOFT;
 		if (clnt->cl_softerr)
diff --git a/net/sunrpc/debugfs.c b/net/sunrpc/debugfs.c
index 56029e3af6ff..79995eb95927 100644
--- a/net/sunrpc/debugfs.c
+++ b/net/sunrpc/debugfs.c
@@ -90,7 +90,7 @@  static int tasks_open(struct inode *inode, struct file *filp)
 		struct seq_file *seq = filp->private_data;
 		struct rpc_clnt *clnt = seq->private = inode->i_private;
 
-		if (!atomic_inc_not_zero(&clnt->cl_count)) {
+		if (!refcount_inc_not_zero(&clnt->cl_count)) {
 			seq_release(inode, filp);
 			ret = -EINVAL;
 		}
diff --git a/net/sunrpc/rpc_pipe.c b/net/sunrpc/rpc_pipe.c
index 09c000d490a1..ee5336d73fdd 100644
--- a/net/sunrpc/rpc_pipe.c
+++ b/net/sunrpc/rpc_pipe.c
@@ -423,7 +423,7 @@  rpc_info_open(struct inode *inode, struct file *file)
 		spin_lock(&file->f_path.dentry->d_lock);
 		if (!d_unhashed(file->f_path.dentry))
 			clnt = RPC_I(inode)->private;
-		if (clnt != NULL && atomic_inc_not_zero(&clnt->cl_count)) {
+		if (clnt != NULL && refcount_inc_not_zero(&clnt->cl_count)) {
 			spin_unlock(&file->f_path.dentry->d_lock);
 			m->private = clnt;
 		} else {