[PATCH bpf 6/8] bpf, sockmap: Several fixes to bpf_msg_push_data

[zijianzhang@xxxxxxxxxxxxx]

From: Zijian Zhang <zijianzhang@xxxxxxxxxxxxx>

Several fixes to bpf_msg_push_data,
1. test_sockmap has tests where bpf_msg_push_data be invoked to push some
data at the end of a message, but -EINVAL is returned for this case.
2. Add logic for corner case where msg->sg.size is zero
3. Before "if (!copy)", the logic for some corner cases related to
msg->sg.end is missing, thus add the logic to handle it.

Fixes: 6fff607e2f14 ("bpf: sk_msg program helper bpf_msg_push_data")
Signed-off-by: Zijian Zhang <zijianzhang@xxxxxxxxxxxxx>
---
 net/core/filter.c | 53 +++++++++++++++++++++++++++++------------------
 1 file changed, 33 insertions(+), 20 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index a88e6924c4c0..4fae427aa5ca 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2793,7 +2793,7 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
 		sk_msg_iter_var_next(i);
 	} while (i != msg->sg.end);
 
-	if (start >= offset + l)
+	if (start > offset + l)
 		return -EINVAL;
 
 	space = MAX_MSG_FRAGS - sk_msg_elem_used(msg);
@@ -2818,6 +2818,8 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
 
 		raw = page_address(page);
 
+		if (i == msg->sg.end)
+			sk_msg_iter_var_prev(i);
 		psge = sk_msg_elem(msg, i);
 		front = start - offset;
 		back = psge->length - front;
@@ -2834,7 +2836,13 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
 		}
 
 		put_page(sg_page(psge));
-	} else if (start - offset) {
+		new = i;
+		goto place_new;
+	}
+
+	if (start - offset) {
+		if (i == msg->sg.end)
+			sk_msg_iter_var_prev(i);
 		psge = sk_msg_elem(msg, i);
 		rsge = sk_msg_elem_cpy(msg, i);
 
@@ -2845,39 +2853,44 @@ BPF_CALL_4(bpf_msg_push_data, struct sk_msg *, msg, u32, start,
 		sk_msg_iter_var_next(i);
 		sg_unmark_end(psge);
 		sg_unmark_end(&rsge);
-		sk_msg_iter_next(msg, end);
 	}
 
 	/* Slot(s) to place newly allocated data */
+	sk_msg_iter_next(msg, end);
 	new = i;
+	sk_msg_iter_var_next(i);
+
+	if (i == msg->sg.end) {
+		if (!rsge.length)
+			goto place_new;
+		sk_msg_iter_next(msg, end);
+		goto place_new;
+	}
 
 	/* Shift one or two slots as needed */
-	if (!copy) {
-		sge = sk_msg_elem_cpy(msg, i);
+	sge = sk_msg_elem_cpy(msg, new);
+	sg_unmark_end(&sge);
 
+	nsge = sk_msg_elem_cpy(msg, i);
+	if (rsge.length) {
 		sk_msg_iter_var_next(i);
-		sg_unmark_end(&sge);
+		nnsge = sk_msg_elem_cpy(msg, i);
 		sk_msg_iter_next(msg, end);
+	}
 
-		nsge = sk_msg_elem_cpy(msg, i);
+	while (i != msg->sg.end) {
+		msg->sg.data[i] = sge;
+		sge = nsge;
+		sk_msg_iter_var_next(i);
 		if (rsge.length) {
-			sk_msg_iter_var_next(i);
+			nsge = nnsge;
 			nnsge = sk_msg_elem_cpy(msg, i);
-		}
-
-		while (i != msg->sg.end) {
-			msg->sg.data[i] = sge;
-			sge = nsge;
-			sk_msg_iter_var_next(i);
-			if (rsge.length) {
-				nsge = nnsge;
-				nnsge = sk_msg_elem_cpy(msg, i);
-			} else {
-				nsge = sk_msg_elem_cpy(msg, i);
-			}
+		} else {
+			nsge = sk_msg_elem_cpy(msg, i);
 		}
 	}
 
+place_new:
 	/* Place newly allocated data buffer */
 	sk_mem_charge(msg->sk, len);
 	msg->sg.size += len;
-- 
2.20.1