The AF_RXRPC procfs helpers format local and remote socket addresses into
fixed 50-byte stack buffers with "%pISpc".

That is too small for the longest current-tree IPv6-with-port form the
formatter can produce. In lib/vsprintf.c, the compressed IPv6 path uses a
dotted-quad tail not only for v4mapped addresses, but also for ISATAP
addresses via ipv6_addr_is_isatap().

As a result, a case such as

  [ffff:ffff:ffff:ffff:0:5efe:255.255.255.255]:65535

is possible with the current formatter. That is 50 visible characters, so
51 bytes including the trailing NUL, which does not fit in the existing
char[50] buffers used by net/rxrpc/proc.c.

Size the buffers from the formatter's maximum textual form and switch the
call sites to scnprintf().

Changes since v1:
- correct the changelog to cite the actual maximum current-tree case
  explicitly
- frame the proof around the ISATAP formatting path instead of the earlier
  mapped-v4 example

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 net/rxrpc/proc.c | 32 ++++++++++++++++++--------------
 1 file changed, 18 insertions(+), 14 deletions(-)

diff --git a/net/rxrpc/proc.c b/net/rxrpc/proc.c
index 59292f7f9205..7925d4569776 100644
--- a/net/rxrpc/proc.c
+++ b/net/rxrpc/proc.c
@@ -10,6 +10,10 @@
 #include <net/af_rxrpc.h>
 #include "ar-internal.h"
 
+#define RXRPC_PROC_ADDRBUF_SIZE \
+	(sizeof("[xxxx:xxxx:xxxx:xxxx:xxxx:xxxx:255.255.255.255]") + \
+	 sizeof(":12345"))
+
 static const char *const rxrpc_conn_states[RXRPC_CONN__NR_STATES] = {
 	[RXRPC_CONN_UNUSED]			= "Unused  ",
 	[RXRPC_CONN_CLIENT_UNSECURED]		= "ClUnsec ",
@@ -53,7 +57,7 @@ static int rxrpc_call_seq_show(struct seq_file *seq, void *v)
 	struct rxrpc_net *rxnet = rxrpc_net(seq_file_net(seq));
 	enum rxrpc_call_state state;
 	rxrpc_seq_t tx_bottom;
-	char lbuff[50], rbuff[50];
+	char lbuff[RXRPC_PROC_ADDRBUF_SIZE], rbuff[RXRPC_PROC_ADDRBUF_SIZE];
 	long timeout = 0;
 
 	if (v == &rxnet->calls) {
@@ -69,11 +73,11 @@ static int rxrpc_call_seq_show(struct seq_file *seq, void *v)
 
 	local = call->local;
 	if (local)
-		sprintf(lbuff, "%pISpc", &local->srx.transport);
+		scnprintf(lbuff, sizeof(lbuff), "%pISpc", &local->srx.transport);
 	else
 		strcpy(lbuff, "no_local");
 
-	sprintf(rbuff, "%pISpc", &call->dest_srx.transport);
+	scnprintf(rbuff, sizeof(rbuff), "%pISpc", &call->dest_srx.transport);
 
 	state = rxrpc_call_state(call);
 	if (state != RXRPC_CALL_SERVER_PREALLOC)
@@ -142,7 +146,7 @@ static int rxrpc_connection_seq_show(struct seq_file *seq, void *v)
 	struct rxrpc_connection *conn;
 	struct rxrpc_net *rxnet = rxrpc_net(seq_file_net(seq));
 	const char *state;
-	char lbuff[50], rbuff[50];
+	char lbuff[RXRPC_PROC_ADDRBUF_SIZE], rbuff[RXRPC_PROC_ADDRBUF_SIZE];
 
 	if (v == &rxnet->conn_proc_list) {
 		seq_puts(seq,
@@ -161,8 +165,8 @@ static int rxrpc_connection_seq_show(struct seq_file *seq, void *v)
 		goto print;
 	}
 
-	sprintf(lbuff, "%pISpc", &conn->local->srx.transport);
-	sprintf(rbuff, "%pISpc", &conn->peer->srx.transport);
+	scnprintf(lbuff, sizeof(lbuff), "%pISpc", &conn->local->srx.transport);
+	scnprintf(rbuff, sizeof(rbuff), "%pISpc", &conn->peer->srx.transport);
 print:
 	state = rxrpc_is_conn_aborted(conn) ?
 		rxrpc_call_completions[conn->completion] :
@@ -228,7 +232,7 @@ static int rxrpc_bundle_seq_show(struct seq_file *seq, void *v)
 {
 	struct rxrpc_bundle *bundle;
 	struct rxrpc_net *rxnet = rxrpc_net(seq_file_net(seq));
-	char lbuff[50], rbuff[50];
+	char lbuff[RXRPC_PROC_ADDRBUF_SIZE], rbuff[RXRPC_PROC_ADDRBUF_SIZE];
 
 	if (v == &rxnet->bundle_proc_list) {
 		seq_puts(seq,
@@ -242,8 +246,8 @@ static int rxrpc_bundle_seq_show(struct seq_file *seq, void *v)
 
 	bundle = list_entry(v, struct rxrpc_bundle, proc_link);
 
-	sprintf(lbuff, "%pISpc", &bundle->local->srx.transport);
-	sprintf(rbuff, "%pISpc", &bundle->peer->srx.transport);
+	scnprintf(lbuff, sizeof(lbuff), "%pISpc", &bundle->local->srx.transport);
+	scnprintf(rbuff, sizeof(rbuff), "%pISpc", &bundle->peer->srx.transport);
 	seq_printf(seq,
 		   "UDP   %-47.47s %-47.47s %4x %3u %3d"
 		   " %c%c%c %08x | %08x %08x %08x %08x %08x\n",
@@ -279,7 +283,7 @@ static int rxrpc_peer_seq_show(struct seq_file *seq, void *v)
 {
 	struct rxrpc_peer *peer;
 	time64_t now;
-	char lbuff[50], rbuff[50];
+	char lbuff[RXRPC_PROC_ADDRBUF_SIZE], rbuff[RXRPC_PROC_ADDRBUF_SIZE];
 
 	if (v == SEQ_START_TOKEN) {
 		seq_puts(seq,
@@ -290,9 +294,9 @@ static int rxrpc_peer_seq_show(struct seq_file *seq, void *v)
 
 	peer = list_entry(v, struct rxrpc_peer, hash_link);
 
-	sprintf(lbuff, "%pISpc", &peer->local->srx.transport);
+	scnprintf(lbuff, sizeof(lbuff), "%pISpc", &peer->local->srx.transport);
 
-	sprintf(rbuff, "%pISpc", &peer->srx.transport);
+	scnprintf(rbuff, sizeof(rbuff), "%pISpc", &peer->srx.transport);
 
 	now = ktime_get_seconds();
 	seq_printf(seq,
@@ -401,7 +405,7 @@ const struct seq_operations rxrpc_peer_seq_ops = {
 static int rxrpc_local_seq_show(struct seq_file *seq, void *v)
 {
 	struct rxrpc_local *local;
-	char lbuff[50];
+	char lbuff[RXRPC_PROC_ADDRBUF_SIZE];
 
 	if (v == SEQ_START_TOKEN) {
 		seq_puts(seq,
@@ -412,7 +416,7 @@ static int rxrpc_local_seq_show(struct seq_file *seq, void *v)
 
 	local = hlist_entry(v, struct rxrpc_local, link);
 
-	sprintf(lbuff, "%pISpc", &local->srx.transport);
+	scnprintf(lbuff, sizeof(lbuff), "%pISpc", &local->srx.transport);
 
 	seq_printf(seq,
 		   "UDP   %-47.47s %3u %3u %3u\n",
-- 
2.50.1 (Apple Git-155)

I'm going to add:

    Fixes: 75b54cb57ca3 ("rxrpc: Add IPv6 support")

and change the subject to "rxrpc: proc:" rather than "rxrpc/proc:"

David

Hi David,

That's possible for some builds, yes.

My concern here is a bit narrower: with the current %pISpc formatter, the
ISATAP case can produce 50 visible characters, i.e. 51 bytes including
the trailing NUL, while these helpers pass a declared char[50] object to
sprintf().

So even if a particular compiler/ABI happens to pad the stack slot out to
sizeof(long) or more, that would only be incidental code generation slack.
It still writes one byte past the end of the declared object, and whether
that lands in padding or in another live stack slot depends on the build
and the specific function layout.

In particular, rxrpc_local_seq_show() has only a single local char[50]
buffer, so there is no source-level guarantee of spare space there either.

The patch is really just making the object size match the formatter's
actual maximum output, so we don't depend on incidental stack padding.

Thanks,
Pengpeng

Pengpeng Hou <pengpeng@iscas.ac.cn> wrote:

> -	char lbuff[50], rbuff[50];
> +	char lbuff[RXRPC_PROC_ADDRBUF_SIZE], rbuff[RXRPC_PROC_ADDRBUF_SIZE];

This might be saved upstream by the compiler padding the buffers out to
sizeof(long) because they're on the stack.

David