netdev - [PATCH][next] tipc: Use size_add() in calls to struct

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Date: Fri, 15 Sep 2023 13:16:26 -0600
From: "Gustavo A. R. Silva" <gustavoars@...nel.org>
To: Jon Maloy <jmaloy@...hat.com>, Ying Xue <ying.xue@...driver.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: netdev@...r.kernel.org, tipc-discussion@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	linux-hardening@...r.kernel.org
Subject: [PATCH][next] tipc: Use size_add() in calls to struct_size()

If, for any reason, the open-coded arithmetic causes a wraparound,
the protection that `struct_size()` adds against potential integer
overflows is defeated. Fix this by hardening call to `struct_size()`
with `size_add()`.

Fixes: e034c6d23bc4 ("tipc: Use struct_size() helper")
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 net/tipc/link.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/tipc/link.c b/net/tipc/link.c
index e33b4f29f77c..d0143823658d 100644
--- a/net/tipc/link.c
+++ b/net/tipc/link.c
@@ -1446,7 +1446,7 @@ u16 tipc_get_gap_ack_blks(struct tipc_gap_ack_blks **ga, struct tipc_link *l,
 		p = (struct tipc_gap_ack_blks *)msg_data(hdr);
 		sz = ntohs(p->len);
 		/* Sanity check */
-		if (sz == struct_size(p, gacks, p->ugack_cnt + p->bgack_cnt)) {
+		if (sz == struct_size(p, gacks, size_add(p->ugack_cnt, p->bgack_cnt))) {
 			/* Good, check if the desired type exists */
 			if ((uc && p->ugack_cnt) || (!uc && p->bgack_cnt))
 				goto ok;
@@ -1533,7 +1533,7 @@ static u16 tipc_build_gap_ack_blks(struct tipc_link *l, struct tipc_msg *hdr)
 			__tipc_build_gap_ack_blks(ga, l, ga->bgack_cnt) : 0;
 
 	/* Total len */
-	len = struct_size(ga, gacks, ga->bgack_cnt + ga->ugack_cnt);
+	len = struct_size(ga, gacks, size_add(ga->bgack_cnt, ga->ugack_cnt));
 	ga->len = htons(len);
 	return len;
 }
-- 
2.34.1