netdev - Re: [PATCH] Truncate UTS_RELEASE for rxrpc version

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Date: Fri, 26 May 2023 11:38:16 +0200
From: Simon Horman <simon.horman@...igine.com>
To: David Howells <dhowells@...hat.com>
Cc: Kenny Ho <Kenny.Ho@....com>, David Laight <David.Laight@...lab.com>,
	Jakub Kicinski <kuba@...nel.org>, Andrew Lunn <andrew@...n.ch>,
	Marc Dionne <marc.dionne@...istor.com>,
	Kenny Ho <y2kenny@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	"linux-afs@...ts.infradead.org" <linux-afs@...ts.infradead.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	alexander.deucher@....com
Subject: Re: [PATCH] Truncate UTS_RELEASE for rxrpc version

On Thu, May 25, 2023 at 11:09:14PM +0100, David Howells wrote:
> Kenny Ho <Kenny.Ho@....com> wrote:
> 
> > @@ -30,6 +28,7 @@ static void rxrpc_send_version_request(struct rxrpc_local *local,
> >  	struct sockaddr_rxrpc srx;
> >  	struct msghdr msg;
> >  	struct kvec iov[2];
> > +	static char rxrpc_version_string[65];
> >  	size_t len;
> >  	int ret;
> >  
> 
> That's not thread-safe.  If you have multiple endpoints each one of them could
> be overwriting the string at the same time.  We can't guarantee that one
> wouldn't corrupt the other.
> 
> There's also no need to reprint it every time; just once during module init
> will do.  How about the attached patch instead?
> 
> David

Thanks David ad Kenny,

can we arrange for a formal posting of the patch below?
I suspect it will languish otherwise.

> ---
> rxrpc: Truncate UTS_RELEASE for rxrpc version
> 
> 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
> running."
> 
> 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@....com>
> Link: https://lore.kernel.org/r/20230523223944.691076-1-Kenny.Ho@amd.com/
> Signed-off-by: David Howells <dhowells@...hat.com>
> Link: https://web.mit.edu/kolya/afs/rx/rx-spec [1]
> cc: Marc Dionne <marc.dionne@...istor.com>
> cc: Andrew Lunn <andrew@...n.ch>
> cc: David Laight <David.Laight@...LAB.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
> ---
>  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,
>  		SLAB_HWCACHE_ALIGN, NULL);
> 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
> 
>