Re: [PATCH net] rxrpc: Truncate UTS_RELEASE for rxrpc version

From: Jeffrey E Altman
Date: Sat May 27 2023 - 10:25:10 EST

On 5/26/2023 7:34 AM, David Howells wrote:
UTS_RELEASE has a maximum length of 64 which can cause rxrpc_version to
exceed the 65 byte message limit.

Per the rx spec[1]: "If a server receives a packet with a type value of 13,
and the client-initiated flag set, it should respond with a 65-byte payload
containing a string that identifies the version of AFS software it is

The current implementation causes a compile error when WERROR is turned on
and/or UTS_RELEASE exceeds the length of 49 (making the version string more
than 64 characters).

Fix this by generating the string during module initialisation and limiting
the UTS_RELEASE segment of the string does not exceed 49 chars. We need to
make sure that the 64 bytes includes "linux-" at the front and " AF_RXRPC"
at the back as this may be used in pattern matching.

Fixes: 44ba06987c0b ("RxRPC: Handle VERSION Rx protocol packets")
Reported-by: Kenny Ho <Kenny.Ho@xxxxxxx>
Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Acked-by: Kenny Ho <Kenny.Ho@xxxxxxx>
cc: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
cc: Andrew Lunn <andrew@xxxxxxx>
cc: David Laight <David.Laight@xxxxxxxxxx>
cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
cc: Eric Dumazet <edumazet@xxxxxxxxxx>
cc: Jakub Kicinski <kuba@xxxxxxxxxx>
cc: Paolo Abeni <pabeni@xxxxxxxxxx>
cc: linux-afs@xxxxxxxxxxxxxxxxxxx
cc: netdev@xxxxxxxxxxxxxxx
Link: [1]
net/rxrpc/af_rxrpc.c | 1 +
net/rxrpc/ar-internal.h | 1 +
net/rxrpc/local_event.c | 11 ++++++++++-
3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/net/rxrpc/af_rxrpc.c b/net/rxrpc/af_rxrpc.c
index 31f738d65f1c..da0b3b5157d5 100644
--- a/net/rxrpc/af_rxrpc.c
+++ b/net/rxrpc/af_rxrpc.c
@@ -980,6 +980,7 @@ static int __init af_rxrpc_init(void)
BUILD_BUG_ON(sizeof(struct rxrpc_skb_priv) > sizeof_field(struct sk_buff, cb));
ret = -ENOMEM;
+ rxrpc_gen_version_string();
rxrpc_call_jar = kmem_cache_create(
"rxrpc_call_jar", sizeof(struct rxrpc_call), 0,
diff --git a/net/rxrpc/ar-internal.h b/net/rxrpc/ar-internal.h
index 5d44dc08f66d..e8e14c6f904d 100644
--- a/net/rxrpc/ar-internal.h
+++ b/net/rxrpc/ar-internal.h
@@ -1068,6 +1068,7 @@ int rxrpc_get_server_data_key(struct rxrpc_connection *, const void *, time64_t,
* local_event.c
+void rxrpc_gen_version_string(void);
void rxrpc_send_version_request(struct rxrpc_local *local,
struct rxrpc_host_header *hdr,
struct sk_buff *skb);
diff --git a/net/rxrpc/local_event.c b/net/rxrpc/local_event.c
index 5e69ea6b233d..993c69f97488 100644
--- a/net/rxrpc/local_event.c
+++ b/net/rxrpc/local_event.c
@@ -16,7 +16,16 @@
#include <generated/utsrelease.h>
#include "ar-internal.h"
-static const char rxrpc_version_string[65] = "linux-" UTS_RELEASE " AF_RXRPC";
+static char rxrpc_version_string[65]; // "linux-" UTS_RELEASE " AF_RXRPC";
+ * Generate the VERSION packet string.
+ */
+void rxrpc_gen_version_string(void)
+ snprintf(rxrpc_version_string, sizeof(rxrpc_version_string),
+ "linux-%.49s AF_RXRPC", UTS_RELEASE);
* Reply to a version request

Reviewed-by: Jeffrey Altman <jaltman@xxxxxxxxxxxx>

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