SUNRPC: Convert from atomic_t to refcount_t on rpc_clnt->cl_count

Commit Message

Xiyu Yang July 17, 2021, 10:18 a.m. UTC

refcount_t type and corresponding API can protect refcounters from
accidental underflow and overflow and further use-after-free situations.

Signed-off-by: Xiyu Yang <[e-mail]>
Signed-off-by: Xin Tan <[e-mail]>
---
 include/linux/sunrpc/clnt.h          |  3 ++-
 net/sunrpc/auth_gss/gss_rpc_upcall.c |  2 +-
 net/sunrpc/clnt.c                    | 14 +++++++-------
 net/sunrpc/debugfs.c                 |  2 +-
 net/sunrpc/rpc_pipe.c                |  2 +-
 5 files changed, 12 insertions(+), 11 deletions(-)

Comments

Trond Myklebust July 17, 2021, 2:43 p.m. UTC | #1

On Sat, 2021-07-17 at 18:18 +0800, Xiyu Yang wrote:
> refcount_t type and corresponding API can protect refcounters from
> accidental underflow and overflow and further use-after-free
> situations.
> 

Have you tested this patch? As far as I remember, the reason why we
never converted is that refcount_inc() gets upset and WARNs when you
bump a zero refcount, like we do very much on purpose in
rpc_free_auth(). Is that no longer the case?

Xiyu Yang July 17, 2021, 4:32 p.m. UTC | #2

Sorry, I'm not sure why you need to bump a zero refcount in a normal situation. But maybe we can use refcount_inc_not_zero() API in rpc_free_auth() instead?

> -----Original Messages-----
> From: "Trond Myklebust" <[e-mail]>
> Sent Time: 2021-07-17 22:43:26 (Saturday)
> To: "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>, "[e-mail]" <[e-mail]>
> Cc: "[e-mail]" <[e-mail]>
> Subject: Re: [PATCH] SUNRPC: Convert from atomic_t to refcount_t on rpc_clnt->cl_count
> 
> On Sat, 2021-07-17 at 18:18 +0800, Xiyu Yang wrote:
> > refcount_t type and corresponding API can protect refcounters from
> > accidental underflow and overflow and further use-after-free
> > situations.
> > 
> 
> Have you tested this patch? As far as I remember, the reason why we
> never converted is that refcount_inc() gets upset and WARNs when you
> bump a zero refcount, like we do very much on purpose in
> rpc_free_auth(). Is that no longer the case?
> 
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> [e-mail]
> 
>

Leon Romanovsky July 18, 2021, 10:47 a.m. UTC | #3

On Sat, Jul 17, 2021 at 02:43:26PM +0000, Trond Myklebust wrote:
> On Sat, 2021-07-17 at 18:18 +0800, Xiyu Yang wrote:
> > refcount_t type and corresponding API can protect refcounters from
> > accidental underflow and overflow and further use-after-free
> > situations.
> > 
> 
> Have you tested this patch? As far as I remember, the reason why we
> never converted is that refcount_inc() gets upset and WARNs when you
> bump a zero refcount, like we do very much on purpose in
> rpc_free_auth(). Is that no longer the case?

It is still the case, they sent gazillion conversion patches with same
mistake.

Thanks

> 
> 
> -- 
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> [e-mail]
> 
>

Patch

diff --git a/include/linux/sunrpc/clnt.h b/include/linux/sunrpc/clnt.h
index 8b5d5c97553e..61f725b9f865 100644
--- a/include/linux/sunrpc/clnt.h
+++ b/include/linux/sunrpc/clnt.h
@@ -10,6 +10,7 @@ 
 #ifndef _LINUX_SUNRPC_CLNT_H
 #define _LINUX_SUNRPC_CLNT_H
 
+#include <linux/refcount.h>
 #include <linux/types.h>
 #include <linux/socket.h>
 #include <linux/in.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..d6b64622bd04 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;
@@ -926,10 +926,10 @@  rpc_free_auth(struct rpc_clnt *clnt)
 	 *       release remaining GSS contexts. This mechanism ensures
 	 *       that it can do so safely.
 	 */
-	atomic_inc(&clnt->cl_count);
+	refcount_inc(&clnt->cl_count);
 	rpcauth_release(clnt->cl_auth);
 	clnt->cl_auth = NULL;
-	if (atomic_dec_and_test(&clnt->cl_count))
+	if (refcount_dec_and_test(&clnt->cl_count))
 		return rpc_free_client(clnt);
 	return NULL;
 }
@@ -943,7 +943,7 @@  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_and_test(&clnt->cl_count))
 			break;
 		clnt = rpc_free_auth(clnt);
 	} while (clnt != NULL);
@@ -1082,7 +1082,7 @@  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 {