[PATCH v2 bpf-next 7/8] bpf, sockmap: Several fixes to bpf_msg_pop_data

[zijianzhang@xxxxxxxxxxxxx]

From: Zijian Zhang <zijianzhang@xxxxxxxxxxxxx>

Several fixes to bpf_msg_pop_data,
1. In sk_msg_shift_left, we should put_page
2. if (len == 0), return early is better
3. pop the entire sk_msg (last == msg->sg.size) should be supported
4. Fix for the value of variable "a"
5. In sk_msg_shift_left, after shifting, i has already pointed to the next
element. Addtional sk_msg_iter_var_next may result in BUG.

Fixes: 7246d8ed4dcc ("bpf: helper to pop data from messages")
Signed-off-by: Zijian Zhang <zijianzhang@xxxxxxxxxxxxx>
---
 net/core/filter.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 4fae427aa5ca..fba445b96de8 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2919,8 +2919,10 @@ static const struct bpf_func_proto bpf_msg_push_data_proto = {
 
 static void sk_msg_shift_left(struct sk_msg *msg, int i)
 {
+	struct scatterlist *sge = sk_msg_elem(msg, i);
 	int prev;
 
+	put_page(sg_page(sge));
 	do {
 		prev = i;
 		sk_msg_iter_var_next(i);
@@ -2957,6 +2959,9 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
 	if (unlikely(flags))
 		return -EINVAL;
 
+	if (unlikely(len == 0))
+		return 0;
+
 	/* First find the starting scatterlist element */
 	i = msg->sg.start;
 	do {
@@ -2969,7 +2974,7 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
 	} while (i != msg->sg.end);
 
 	/* Bounds checks: start and pop must be inside message */
-	if (start >= offset + l || last >= msg->sg.size)
+	if (start >= offset + l || last > msg->sg.size)
 		return -EINVAL;
 
 	space = MAX_MSG_FRAGS - sk_msg_elem_used(msg);
@@ -2998,12 +3003,12 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
 	 */
 	if (start != offset) {
 		struct scatterlist *nsge, *sge = sk_msg_elem(msg, i);
-		int a = start;
+		int a = start - offset;
 		int b = sge->length - pop - a;
 
 		sk_msg_iter_var_next(i);
 
-		if (pop < sge->length - a) {
+		if (b > 0) {
 			if (space) {
 				sge->length = a;
 				sk_msg_shift_right(msg, i);
@@ -3022,7 +3027,6 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
 				if (unlikely(!page))
 					return -ENOMEM;
 
-				sge->length = a;
 				orig = sg_page(sge);
 				from = sg_virt(sge);
 				to = page_address(page);
@@ -3032,7 +3036,7 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
 				put_page(orig);
 			}
 			pop = 0;
-		} else if (pop >= sge->length - a) {
+		} else {
 			pop -= (sge->length - a);
 			sge->length = a;
 		}
@@ -3066,7 +3070,6 @@ BPF_CALL_4(bpf_msg_pop_data, struct sk_msg *, msg, u32, start,
 			pop -= sge->length;
 			sk_msg_shift_left(msg, i);
 		}
-		sk_msg_iter_var_next(i);
 	}
 
 	sk_mem_uncharge(msg->sk, len - pop);
-- 
2.20.1