[PATCH v2 bpf-next 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 is invoked to push some
data at the end of a message, but -EINVAL is returned. In this case, in
bpf_msg_push_data, after the first loop, i will be set to msg->sg.end, add
the logic to handle it.
2. In the code block of "if (start - offset)", it's possible that "i"
points to the last of sk_msg_elem. In this case, "sk_msg_iter_next(msg,
end)" might still be called twice, another invoking is in "if (!copy)"
code block, but actually only one is needed. Add the logic to handle it,
and reconstruct the code to make the logic more clear.

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