[PATCH net] ebpf: fix bpf_msg_pull_data

[Tushar Dave <tushar.n.dave@oracle.com>]

While doing some preliminary testing it is found that bpf helper
bpf_msg_pull_data does not calculate the data and data_end offset
correctly. Fix it!

Fixes: 015632bb30da ("bpf: sk_msg program helper bpf_sk_msg_pull_data")
Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
Acked-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
---
 net/core/filter.c | 38 +++++++++++++++++++++++++-------------
 1 file changed, 25 insertions(+), 13 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index c25eb36..3eeb3d6 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2285,7 +2285,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
 BPF_CALL_4(bpf_msg_pull_data,
 	   struct sk_msg_buff *, msg, u32, start, u32, end, u64, flags)
 {
-	unsigned int len = 0, offset = 0, copy = 0;
+	unsigned int len = 0, offset = 0, copy = 0, off = 0;
 	struct scatterlist *sg = msg->sg_data;
 	int first_sg, last_sg, i, shift;
 	unsigned char *p, *to, *from;
@@ -2299,22 +2299,30 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
 	i = msg->sg_start;
 	do {
 		len = sg[i].length;
-		offset += len;
 		if (start < offset + len)
 			break;
+		offset += len;
 		i++;
 		if (i == MAX_SKB_FRAGS)
 			i = 0;
-	} while (i != msg->sg_end);
+	} while (i <= msg->sg_end);
 
+	/* return error if start is out of range */
 	if (unlikely(start >= offset + len))
 		return -EINVAL;
 
-	if (!msg->sg_copy[i] && bytes <= len)
-		goto out;
+	/* return error if i is last entry in sglist and end is out of range */
+	if (msg->sg_copy[i] && end > offset + len)
+		return -EINVAL;
 
 	first_sg = i;
 
+	/* if i is not last entry in sg list and end (i.e start + bytes) is
+	 * within this sg[i] then goto out and calculate data and data_end
+	 */
+	if (!msg->sg_copy[i] && end <= offset + len)
+		goto out;
+
 	/* At this point we need to linearize multiple scatterlist
 	 * elements or a single shared page. Either way we need to
 	 * copy into a linear buffer exclusively owned by BPF. Then
@@ -2330,9 +2338,14 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
 		i++;
 		if (i == MAX_SKB_FRAGS)
 			i = 0;
-		if (bytes < copy)
+		if (end < copy)
 			break;
-	} while (i != msg->sg_end);
+	} while (i <= msg->sg_end);
+
+	/* return error if i is last entry in sglist and end is out of range */
+	if (i > msg->sg_end && end > offset + copy)
+		return -EINVAL;
+
 	last_sg = i;
 
 	if (unlikely(copy < end - start))
@@ -2342,23 +2355,22 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
 	if (unlikely(!page))
 		return -ENOMEM;
 	p = page_address(page);
-	offset = 0;
 
 	i = first_sg;
 	do {
 		from = sg_virt(&sg[i]);
 		len = sg[i].length;
-		to = p + offset;
+		to = p + off;
 
 		memcpy(to, from, len);
-		offset += len;
+		off += len;
 		sg[i].length = 0;
 		put_page(sg_page(&sg[i]));
 
 		i++;
 		if (i == MAX_SKB_FRAGS)
 			i = 0;
-	} while (i != last_sg);
+	} while (i < last_sg);
 
 	sg[first_sg].length = copy;
 	sg_set_page(&sg[first_sg], page, copy, 0);
@@ -2380,7 +2392,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
 		else
 			move_from = i + shift;
 
-		if (move_from == msg->sg_end)
+		if (move_from > msg->sg_end)
 			break;
 
 		sg[i] = sg[move_from];
@@ -2396,7 +2408,7 @@ struct sock *do_msg_redirect_map(struct sk_msg_buff *msg)
 	if (msg->sg_end < 0)
 		msg->sg_end += MAX_SKB_FRAGS;
 out:
-	msg->data = sg_virt(&sg[i]) + start - offset;
+	msg->data = sg_virt(&sg[first_sg]) + start - offset;
 	msg->data_end = msg->data + bytes;
 
 	return 0;
-- 
1.8.3.1