[SCSI] libiscsi_tcp: fix max_r2t manipulation

Problem description from Xi Wang:
A large max_r2t could lead to integer overflow in subsequent call to
iscsi_tcp_r2tpool_alloc(), allocating a smaller buffer than expected
and leading to out-of-bounds write.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

6 files changed, 24 insertions, 26 deletions

diff --git a/drivers/scsi/cxgbi/libcxgbi.c b/drivers/scsi/cxgbi/libcxgbi.c
index d3ff9cd40234..e6e6aa9289b8 100644
--- a/drivers/scsi/cxgbi/libcxgbi.c
+++ b/drivers/scsi/cxgbi/libcxgbi.c
@@ -2148,11 +2148,10 @@ int cxgbi_set_conn_param(struct iscsi_cls_conn *cls_conn,
                         enum iscsi_param param, char *buf, int buflen)
 {
         struct iscsi_conn *conn = cls_conn->dd_data;
-        struct iscsi_session *session = conn->session;
         struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
         struct cxgbi_conn *cconn = tcp_conn->dd_data;
         struct cxgbi_sock *csk = cconn->cep->csk;
-        int value, err = 0;
+        int err;
 
         log_debug(1 << CXGBI_DBG_ISCSI,
                 "cls_conn 0x%p, param %d, buf(%d) %s.\n",
@@ -2174,15 +2173,7 @@ int cxgbi_set_conn_param(struct iscsi_cls_conn *cls_conn,
                                                         conn->datadgst_en, 0);
                 break;
         case ISCSI_PARAM_MAX_R2T:
-                sscanf(buf, "%d", &value);
-                if (value <= 0 || !is_power_of_2(value))
-                        return -EINVAL;
-                if (session->max_r2t == value)
-                        break;
-                iscsi_tcp_r2tpool_free(session);
-                err = iscsi_set_param(cls_conn, param, buf, buflen);
-                if (!err && iscsi_tcp_r2tpool_alloc(session))
-                        return -ENOMEM;
+                return iscsi_tcp_set_max_r2t(conn, buf);
         case ISCSI_PARAM_MAX_RECV_DLENGTH:
                 err = iscsi_set_param(cls_conn, param, buf, buflen);
                 if (!err)
diff --git a/drivers/scsi/iscsi_tcp.c b/drivers/scsi/iscsi_tcp.c
index db47158e0dde..453a740fa68e 100644
--- a/drivers/scsi/iscsi_tcp.c
+++ b/drivers/scsi/iscsi_tcp.c
@@ -684,10 +684,8 @@ static int iscsi_sw_tcp_conn_set_param(struct iscsi_cls_conn *cls_conn,
                                        int buflen)
 {
         struct iscsi_conn *conn = cls_conn->dd_data;
-        struct iscsi_session *session = conn->session;
         struct iscsi_tcp_conn *tcp_conn = conn->dd_data;
         struct iscsi_sw_tcp_conn *tcp_sw_conn = tcp_conn->dd_data;
-        int value;
 
         switch(param) {
         case ISCSI_PARAM_HDRDGST_EN:
@@ -699,16 +697,7 @@ static int iscsi_sw_tcp_conn_set_param(struct iscsi_cls_conn *cls_conn,
                         sock_no_sendpage : tcp_sw_conn->sock->ops->sendpage;
                 break;
         case ISCSI_PARAM_MAX_R2T:
-                sscanf(buf, "%d", &value);
-                if (value <= 0 || !is_power_of_2(value))
-                        return -EINVAL;
-                if (session->max_r2t == value)
-                        break;
-                iscsi_tcp_r2tpool_free(session);
-                iscsi_set_param(cls_conn, param, buf, buflen);
-                if (iscsi_tcp_r2tpool_alloc(session))
-                        return -ENOMEM;
-                break;
+                return iscsi_tcp_set_max_r2t(conn, buf);
         default:
                 return iscsi_set_param(cls_conn, param, buf, buflen);
         }
diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
index 00592e3bb375..8582d7c25732 100644
--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -3201,7 +3201,7 @@ int iscsi_set_param(struct iscsi_cls_conn *cls_conn,
                 sscanf(buf, "%d", &session->initial_r2t_en);
                 break;
         case ISCSI_PARAM_MAX_R2T:
-                sscanf(buf, "%d", &session->max_r2t);
+                sscanf(buf, "%hu", &session->max_r2t);
                 break;
         case ISCSI_PARAM_IMM_DATA_EN:
                 sscanf(buf, "%d", &session->imm_data_en);
diff --git a/drivers/scsi/libiscsi_tcp.c b/drivers/scsi/libiscsi_tcp.c
index 5715a3d0a3d3..c4996b081999 100644
--- a/drivers/scsi/libiscsi_tcp.c
+++ b/drivers/scsi/libiscsi_tcp.c
@@ -1170,6 +1170,24 @@ void iscsi_tcp_r2tpool_free(struct iscsi_session *session)
 }
 EXPORT_SYMBOL_GPL(iscsi_tcp_r2tpool_free);
 
+int iscsi_tcp_set_max_r2t(struct iscsi_conn *conn, char *buf)
+{
+        struct iscsi_session *session = conn->session;
+        unsigned short r2ts = 0;
+
+        sscanf(buf, "%hu", &r2ts);
+        if (session->max_r2t == r2ts)
+                return 0;
+
+        if (!r2ts || !is_power_of_2(r2ts))
+                return -EINVAL;
+
+        session->max_r2t = r2ts;
+        iscsi_tcp_r2tpool_free(session);
+        return iscsi_tcp_r2tpool_alloc(session);
+}
+EXPORT_SYMBOL_GPL(iscsi_tcp_set_max_r2t);
+
 void iscsi_tcp_conn_get_stats(struct iscsi_cls_conn *cls_conn,
                               struct iscsi_stats *stats)
 {
diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h
index 2e42e9a0e0b6..6e33386a3898 100644
--- a/include/scsi/libiscsi.h
+++ b/include/scsi/libiscsi.h
@@ -268,7 +268,7 @@ struct iscsi_session {
         int                     lu_reset_timeout;
         int                     tgt_reset_timeout;
         int                     initial_r2t_en;
-        unsigned                max_r2t;
+        unsigned short          max_r2t;
         int                     imm_data_en;
         unsigned                first_burst;
         unsigned                max_burst;
diff --git a/include/scsi/libiscsi_tcp.h b/include/scsi/libiscsi_tcp.h
index ac0cc1d925ef..215469a9b801 100644
--- a/include/scsi/libiscsi_tcp.h
+++ b/include/scsi/libiscsi_tcp.h
@@ -128,7 +128,7 @@ extern void iscsi_tcp_conn_teardown(struct iscsi_cls_conn *cls_conn);
 /* misc helpers */
 extern int iscsi_tcp_r2tpool_alloc(struct iscsi_session *session);
 extern void iscsi_tcp_r2tpool_free(struct iscsi_session *session);
-
+extern int iscsi_tcp_set_max_r2t(struct iscsi_conn *conn, char *buf);
 extern void iscsi_tcp_conn_get_stats(struct iscsi_cls_conn *cls_conn,
                                      struct iscsi_stats *stats);
 #endif /* LIBISCSI_TCP_H */