[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>

1 files changed, 18 insertions, 0 deletions

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)
 {