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

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Message-ID: <675150.1609954812@warthog.procyon.org.uk>
Date:   Wed, 06 Jan 2021 17:40:12 +0000
From:   David Howells <dhowells@...hat.com>
To:     Tom Rix <trix@...hat.com>
Cc:     dhowells@...hat.com, 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()

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;
 		}
 
 		_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, ==,