linux-kernel - [PATCH] rxrpc: fix handling of an unsupported token type in rxrpc

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Date:   Tue, 29 Dec 2020 09:39:16 -0800
From:   trix@...hat.com
To:     dhowells@...hat.com, davem@...emloft.net, kuba@...nel.org,
        natechancellor@...il.com, ndesaulniers@...gle.com
Cc:     linux-afs@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, clang-built-linux@...glegroups.com,
        Tom Rix <trix@...hat.com>
Subject: [PATCH] rxrpc: fix handling of an unsupported token type in rxrpc_read()

From: Tom Rix <trix@...hat.com>

clang static analysis reports this problem

net/rxrpc/key.c:657:11: warning: Assigned value is garbage or undefined
                toksize = toksizes[tok++];
                        ^ ~~~~~~~~~~~~~~~

rxrpc_read() contains two 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.

Change the error handling in the second loop to be consistent with
the first.  Simplify the error handling to an if check.

Fixes: 9a059cd5ca7d ("rxrpc: Downgrade the BUG() for unsupported token type in rxrpc_read()")
Signed-off-by: Tom Rix <trix@...hat.com>
---
 net/rxrpc/key.c | 48 ++++++++++++++++++++++--------------------------
 1 file changed, 22 insertions(+), 26 deletions(-)

diff --git a/net/rxrpc/key.c b/net/rxrpc/key.c
index 9631aa8543b5..eea877ee6ab3 100644
--- a/net/rxrpc/key.c
+++ b/net/rxrpc/key.c
@@ -587,20 +587,19 @@ static long rxrpc_read(const struct key *key,
 	for (token = key->payload.data[0]; token; token = token->next) {
 		toksize = 4;	/* sec index */
 
-		switch (token->security_index) {
-		case RXRPC_SECURITY_RXKAD:
-			toksize += 8 * 4;	/* viceid, kvno, key*2, begin,
-						 * end, primary, tktlen */
-			if (!token->no_leak_key)
-				toksize += RND(token->kad->ticket_len);
-			break;
-
-		default: /* we have a ticket we can't encode */
+		if (token->security_index != RXRPC_SECURITY_RXKAD) {
+			/* we have a ticket we can't encode */
 			pr_err("Unsupported key token type (%u)\n",
 			       token->security_index);
 			continue;
 		}
 
+		/* viceid, kvno, key*2, begin, end, primary, tktlen */
+		toksize += 8 * 4;
+
+		if (!token->no_leak_key)
+			toksize += RND(token->kad->ticket_len);
+
 		_debug("token[%u]: toksize=%u", ntoks, toksize);
 		ASSERTCMP(toksize, <=, AFSTOKEN_LENGTH_MAX);
 
@@ -654,28 +653,25 @@ static long rxrpc_read(const struct key *key,
 
 	tok = 0;
 	for (token = key->payload.data[0]; token; token = token->next) {
+		/* error reported above */
+		if (token->security_index != RXRPC_SECURITY_RXKAD)
+			continue;
+
 		toksize = toksizes[tok++];
 		ENCODE(toksize);
 		oldxdr = xdr;
 		ENCODE(token->security_index);
 
-		switch (token->security_index) {
-		case RXRPC_SECURITY_RXKAD:
-			ENCODE(token->kad->vice_id);
-			ENCODE(token->kad->kvno);
-			ENCODE_BYTES(8, token->kad->session_key);
-			ENCODE(token->kad->start);
-			ENCODE(token->kad->expiry);
-			ENCODE(token->kad->primary_flag);
-			if (token->no_leak_key)
-				ENCODE(0);
-			else
-				ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
-			break;
-
-		default:
-			break;
-		}
+		ENCODE(token->kad->vice_id);
+		ENCODE(token->kad->kvno);
+		ENCODE_BYTES(8, token->kad->session_key);
+		ENCODE(token->kad->start);
+		ENCODE(token->kad->expiry);
+		ENCODE(token->kad->primary_flag);
+		if (token->no_leak_key)
+			ENCODE(0);
+		else
+			ENCODE_DATA(token->kad->ticket_len, token->kad->ticket);
 
 		ASSERTCMP((unsigned long)xdr - (unsigned long)oldxdr, ==,
 			  toksize);
-- 
2.27.0