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

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Message-ID: <84871.1682082533@warthog.procyon.org.uk>
Date:   Fri, 21 Apr 2023 14:08:53 +0100
From:   David Howells <dhowells@...hat.com>
To:     netdev@...r.kernel.org
cc:     dhowells@...hat.com, "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Simon Horman <simon.horman@...igine.com>,
        Kees Cook <keescook@...omium.org>,
        Jeffrey Altman <jaltman@...istor.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>, linux-afs@...ts.infradead.org,
        linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net-next] rxrpc: Replace fake flex-array with flexible-array member


From: Gustavo A. R. Silva <gustavoars@...nel.org>

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>
Signed-off-by: David Howells <dhowells@...hat.com>
Reviewed-by: Simon Horman <simon.horman@...igine.com>
Reviewed-by: Kees Cook <keescook@...omium.org>
Reviewed-by: Jeffrey Altman <jaltman@...istor.com>
cc: Marc Dionne <marc.dionne@...istor.com>
cc: "David S. Miller" <davem@...emloft.net>
cc: Eric Dumazet <edumazet@...gle.com>
cc: Jakub Kicinski <kuba@...nel.org>
cc: Paolo Abeni <pabeni@...hat.com>
cc: linux-afs@...ts.infradead.org
cc: netdev@...r.kernel.org
cc: linux-hardening@...r.kernel.org
Link: https://lore.kernel.org/r/ZAZT11n4q5bBttW0@work/
---
 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