linux-hardening - [PATCH][next] rxrpc: Replace fake flex-array with flexible-array member

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Date:   Mon, 6 Mar 2023 14:57:59 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     David Howells <dhowells@...hat.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     linux-afs@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-hardening@...r.kernel.org
Subject: [PATCH][next] rxrpc: Replace fake flex-array with flexible-array
 member

Zero-length arrays as fake flexible arrays are deprecated and we are
moving towards adopting C99 flexible-array members instead.

Transform zero-length array into flexible-array member in struct
rxrpc_ackpacket.

Address the following warnings found with GCC-13 and
-fstrict-flex-arrays=3 enabled:
net/rxrpc/call_event.c:149:38: warning: array subscript i is outside array bounds of ‘uint8_t[0]’ {aka ‘unsigned char[]’} [-Warray-bounds=]

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [1].

Link: https://github.com/KSPP/linux/issues/21
Link: https://github.com/KSPP/linux/issues/263
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [1]
Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
---
 net/rxrpc/protocol.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rxrpc/protocol.h b/net/rxrpc/protocol.h
index 6760cb99c6d6..e8ee4af43ca8 100644
--- a/net/rxrpc/protocol.h
+++ b/net/rxrpc/protocol.h
@@ -126,7 +126,7 @@ struct rxrpc_ackpacket {
 	uint8_t		nAcks;		/* number of ACKs */
 #define RXRPC_MAXACKS	255
 
-	uint8_t		acks[0];	/* list of ACK/NAKs */
+	uint8_t		acks[];		/* list of ACK/NAKs */
 #define RXRPC_ACK_TYPE_NACK		0
 #define RXRPC_ACK_TYPE_ACK		1
 
-- 
2.34.1