sunrpc: fix RCU handling of gc_ctx field

The handling of the gc_ctx pointer only seems to be partially RCU-safe.
The assignment and freeing are done using RCU, but many places in the
code seem to dereference that pointer without proper RCU safeguards.

Fix them to use rcu_dereference and to rcu_read_lock/unlock, and to
properly handle the case where the pointer is NULL.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

1 files changed, 35 insertions, 17 deletions

diff --git a/net/sunrpc/auth_gss/auth_gss.c b/net/sunrpc/auth_gss/auth_gss.c
index 73854314fb85..afb292cd797d 100644
--- a/net/sunrpc/auth_gss/auth_gss.c
+++ b/net/sunrpc/auth_gss/auth_gss.c
@@ -183,8 +183,9 @@ gss_cred_get_ctx(struct rpc_cred *cred)
         struct gss_cl_ctx *ctx = NULL;
 
         rcu_read_lock();
-        if (gss_cred->gc_ctx)
-                ctx = gss_get_ctx(gss_cred->gc_ctx);
+        ctx = rcu_dereference(gss_cred->gc_ctx);
+        if (ctx)
+                gss_get_ctx(ctx);
         rcu_read_unlock();
         return ctx;
 }
@@ -1207,13 +1208,13 @@ gss_destroying_context(struct rpc_cred *cred)
 {
         struct gss_cred *gss_cred = container_of(cred, struct gss_cred, gc_base);
         struct gss_auth *gss_auth = container_of(cred->cr_auth, struct gss_auth, rpc_auth);
+        struct gss_cl_ctx *ctx = rcu_dereference_protected(gss_cred->gc_ctx, 1);
         struct rpc_task *task;
 
-        if (gss_cred->gc_ctx == NULL ||
-            test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) == 0)
+        if (test_bit(RPCAUTH_CRED_UPTODATE, &cred->cr_flags) == 0)
                 return 0;
 
-        gss_cred->gc_ctx->gc_proc = RPC_GSS_PROC_DESTROY;
+        ctx->gc_proc = RPC_GSS_PROC_DESTROY;
         cred->cr_ops = &gss_nullops;
 
         /* Take a reference to ensure the cred will be destroyed either
@@ -1274,7 +1275,7 @@ gss_destroy_nullcred(struct rpc_cred *cred)
 {
         struct gss_cred *gss_cred = container_of(cred, struct gss_cred, gc_base);
         struct gss_auth *gss_auth = container_of(cred->cr_auth, struct gss_auth, rpc_auth);
-        struct gss_cl_ctx *ctx = gss_cred->gc_ctx;
+        struct gss_cl_ctx *ctx = rcu_dereference_protected(gss_cred->gc_ctx, 1);
 
         RCU_INIT_POINTER(gss_cred->gc_ctx, NULL);
         call_rcu(&cred->cr_rcu, gss_free_cred_callback);
@@ -1349,20 +1350,30 @@ gss_cred_init(struct rpc_auth *auth, struct rpc_cred *cred)
 static char *
 gss_stringify_acceptor(struct rpc_cred *cred)
 {
-        char *string;
+        char *string = NULL;
         struct gss_cred *gss_cred = container_of(cred, struct gss_cred, gc_base);
-        struct xdr_netobj *acceptor = &gss_cred->gc_ctx->gc_acceptor;
+        struct gss_cl_ctx *ctx;
+        struct xdr_netobj *acceptor;
+
+        rcu_read_lock();
+        ctx = rcu_dereference(gss_cred->gc_ctx);
+        if (!ctx)
+                goto out;
+
+        acceptor = &ctx->gc_acceptor;
 
         /* no point if there's no string */
         if (!acceptor->len)
-                return NULL;
+                goto out;
 
         string = kmalloc(acceptor->len + 1, GFP_KERNEL);
         if (!string)
-                return string;
+                goto out;
 
         memcpy(string, acceptor->data, acceptor->len);
         string[acceptor->len] = '\0';
+out:
+        rcu_read_unlock();
         return string;
 }
 
@@ -1374,15 +1385,16 @@ static int
 gss_key_timeout(struct rpc_cred *rc)
 {
         struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base);
+        struct gss_cl_ctx *ctx;
         unsigned long now = jiffies;
         unsigned long expire;
 
-        if (gss_cred->gc_ctx == NULL)
-                return -EACCES;
-
-        expire = gss_cred->gc_ctx->gc_expiry - (gss_key_expire_timeo * HZ);
-
-        if (time_after(now, expire))
+        rcu_read_lock();
+        ctx = rcu_dereference(gss_cred->gc_ctx);
+        if (ctx)
+                expire = ctx->gc_expiry - (gss_key_expire_timeo * HZ);
+        rcu_read_unlock();
+        if (!ctx || time_after(now, expire))
                 return -EACCES;
         return 0;
 }
@@ -1391,13 +1403,19 @@ static int
 gss_match(struct auth_cred *acred, struct rpc_cred *rc, int flags)
 {
         struct gss_cred *gss_cred = container_of(rc, struct gss_cred, gc_base);
+        struct gss_cl_ctx *ctx;
         int ret;
 
         if (test_bit(RPCAUTH_CRED_NEW, &rc->cr_flags))
                 goto out;
         /* Don't match with creds that have expired. */
-        if (time_after(jiffies, gss_cred->gc_ctx->gc_expiry))
+        rcu_read_lock();
+        ctx = rcu_dereference(gss_cred->gc_ctx);
+        if (!ctx || time_after(jiffies, ctx->gc_expiry)) {
+                rcu_read_unlock();
                 return 0;
+        }
+        rcu_read_unlock();
         if (!test_bit(RPCAUTH_CRED_UPTODATE, &rc->cr_flags))
                 return 0;
 out: