netdev - Re: [PATCH] rxrpc: fix handling of an unsupported token type in rxrpc

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Message-ID: <f02bdada-355c-97cd-bc32-f84516ddd93f@redhat.com>
Date:   Wed, 6 Jan 2021 11:34:17 -0800
From:   Tom Rix <trix@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     davem@...emloft.net, kuba@...nel.org, natechancellor@...il.com,
        ndesaulniers@...gle.com, linux-afs@...ts.infradead.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] rxrpc: fix handling of an unsupported token type in
 rxrpc_read()


On 1/6/21 9:40 AM, David Howells wrote:
> David Howells <dhowells@...hat.com> wrote:
>
>> How about this?
>> ...
>>     Fix the second loop so that it doesn't encode the size and type of an
>>     unsupported token, but rather just ignore it as does the first loop.
> Actually, a better way is probably just to error out in this case.  This
> should only happen if a new token type is incompletely implemented.
>
> David
> ---
> commit e68ef16f59aa57564761b21e5ecb2ebbd72d1c57
> Author: David Howells <dhowells@...hat.com>
> Date:   Wed Jan 6 16:21:40 2021 +0000
>
>     rxrpc: Fix handling of an unsupported token type in rxrpc_read()
>     
>     Clang static analysis reports the following:
>     
>     net/rxrpc/key.c:657:11: warning: Assigned value is garbage or undefined
>                     toksize = toksizes[tok++];
>                             ^ ~~~~~~~~~~~~~~~
>     
>     rxrpc_read() contains two consecutive loops.  The first loop calculates the
>     token sizes and stores the results in toksizes[] and the second one uses
>     the array.  When there is an error in identifying the token in the first
>     loop, the token is skipped, no change is made to the toksizes[] array.
>     When the same error happens in the second loop, the token is not skipped.
>     This will cause the toksizes[] array to be out of step and will overrun
>     past the calculated sizes.
>     
>     Fix this by making both loops log a message and return an error in this
>     case.  This should only happen if a new token type is incompletely
>     implemented, so it should normally be impossible to trigger this.
>     
>     Fixes: 9a059cd5ca7d ("rxrpc: Downgrade the BUG() for unsupported token type in rxrpc_read()")
>     Reported-by: Tom Rix <trix@...hat.com>
>     Signed-off-by: David Howells <dhowells@...hat.com>
>
> diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
> index 9631aa8543b5..8d2073e0e3da 100644
> --- a/net/rxrpc/key.c
> +++ b/net/rxrpc/key.c
> @@ -598,7 +598,7 @@ static long rxrpc_read(const struct key *key,
>  		default: /* we have a ticket we can't encode */
>  			pr_err("Unsupported key token type (%u)\n",
>  			       token->security_index);
> -			continue;
> +			return -ENOPKG;
>  		}

These two loops iterate over the same data, i believe returning here is all that is needed.

Tom

>  
>  		_debug("token[%u]: toksize=%u", ntoks, toksize);
> @@ -674,7 +674,9 @@ static long rxrpc_read(const struct key *key,
>  			break;
>  
>  		default:
> -			break;
> +			pr_err("Unsupported key token type (%u)\n",
> +			       token->security_index);
> +			return -ENOPKG;
>  		}
>  
>  		ASSERTCMP((unsigned long)xdr - (unsigned long)oldxdr, ==,
>