mei: fix possible integer overflow issue

There is a possible integer overflow following by a buffer overflow
when accumulating messages coming from the FW to compose a full payload.
Occurrence of wrap around has to be prevented for next message size
calculation.
For unsigned integer the addition overflow has occurred when the
result is smaller than one of the arguments.
To simplify the fix, the types of buf.size and buf_idx are set to the
same width, namely size_t also to be aligned with the type of length
parameter in file read/write ops.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 16 insertions, 5 deletions

diff --git a/drivers/misc/mei/interrupt.c b/drivers/misc/mei/interrupt.c
index 6340dee33052..b8aa047ec258 100644
--- a/drivers/misc/mei/interrupt.c
+++ b/drivers/misc/mei/interrupt.c
@@ -104,6 +104,7 @@ int mei_cl_irq_read_msg(struct mei_cl *cl,
 	struct mei_device *dev = cl->dev;
 	struct mei_cl_cb *cb;
 	unsigned char *buffer = NULL;
+	size_t buf_sz;
 
 	cb = list_first_entry_or_null(&cl->rd_pending, struct mei_cl_cb, list);
 	if (!cb) {
@@ -124,11 +125,21 @@ int mei_cl_irq_read_msg(struct mei_cl *cl,
 		goto out;
 	}
 
-	if (cb->buf.size < mei_hdr->length + cb->buf_idx) {
-		cl_dbg(dev, cl, "message overflow. size %d len %d idx %ld\n",
+	buf_sz = mei_hdr->length + cb->buf_idx;
+	/* catch for integer overflow */
+	if (buf_sz < cb->buf_idx) {
+		cl_err(dev, cl, "message is too big len %d idx %ld\n",
+		       mei_hdr->length, cb->buf_idx);
+
+		list_move_tail(&cb->list, &complete_list->list);
+		cb->status = -EMSGSIZE;
+		goto out;
+	}
+
+	if (cb->buf.size < buf_sz) {
+		cl_dbg(dev, cl, "message overflow. size %zd len %d idx %zd\n",
 			cb->buf.size, mei_hdr->length, cb->buf_idx);
-		buffer = krealloc(cb->buf.data, mei_hdr->length + cb->buf_idx,
-				  GFP_KERNEL);
+		buffer = krealloc(cb->buf.data, buf_sz, GFP_KERNEL);
 
 		if (!buffer) {
 			cb->status = -ENOMEM;
@@ -136,7 +147,7 @@ int mei_cl_irq_read_msg(struct mei_cl *cl,
 			goto out;
 		}
 		cb->buf.data = buffer;
-		cb->buf.size = mei_hdr->length + cb->buf_idx;
+		cb->buf.size = buf_sz;
 	}
 
 	buffer = cb->buf.data + cb->buf_idx;