From:   Chuck Lever <chuck.lever@oracle.com>
To:     linux-nfs@vger.kernel.org
Cc:     rostedt@goodmis.org
Subject: [PATCH v1] SUNRPC: Fix sockaddr handling in the svc_xprt_create_error trace point
Date:   Sun,  9 Jan 2022 13:26:51 -0500
Message-Id:  <164175281165.5206.17055902557192579968.stgit@morisot.1015granger.net>
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While testing, I got an unexpected KASAN splat:

Jan 08 13:50:27 oracle-102.nfsv4.dev kernel: BUG: KASAN: stack-out-of-bounds in trace_event_raw_event_svc_xprt_create_err+0x190/0x210 [sunrpc]
Jan 08 13:50:27 oracle-102.nfsv4.dev kernel: Read of size 28 at addr ffffc9000008f728 by task mount.nfs/4628

The memcpy() in the TP_fast_assign section copies the size of the
destination buffer in order that the buffer won't be overrun. In
many other trace points, the source buffer is a "struct
sockaddr_storage" so the actual length of the source buffer is
always long enough to prevent reading from uninitialized or
unallocated memory.

However, for this trace point, the source buffer can be as small as
a "struct sockaddr_in". For AF_INET sockaddrs, the memcpy() reads
memory that follows source buffer, which is not always valid memory.

To avoid copying past the end of the passed-in sockaddr, make the
source address's length available to the memcpy(). It would be a
little nicer if the tracing infrastructure was more friendly about
storing socket addresses that are not AF_INET, but I could not find
a way to make "%pIS" work with a dynamic array.

Reported-by: KASAN
Fixes: 4b8f380e46e4 ("SUNRPC: Tracepoint to record errors in svc_xpo_create()")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 include/trace/events/sunrpc.h |    5 +++--
 net/sunrpc/svc_xprt.c         |    2 +-
 2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 3a99358c262b..dd4cfd117844 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1744,10 +1744,11 @@ TRACE_EVENT(svc_xprt_create_err,
 		const char *program,
 		const char *protocol,
 		struct sockaddr *sap,
+		size_t saplen,
 		const struct svc_xprt *xprt
 	),
 
-	TP_ARGS(program, protocol, sap, xprt),
+	TP_ARGS(program, protocol, sap, saplen, xprt),
 
 	TP_STRUCT__entry(
 		__field(long, error)
@@ -1760,7 +1761,7 @@ TRACE_EVENT(svc_xprt_create_err,
 		__entry->error = PTR_ERR(xprt);
 		__assign_str(program, program);
 		__assign_str(protocol, protocol);
-		memcpy(__entry->addr, sap, sizeof(__entry->addr));
+		memcpy(__entry->addr, sap, min(saplen, sizeof(__entry->addr)));
 	),
 
 	TP_printk("addr=%pISpc program=%s protocol=%s error=%ld",
diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
index 1e99ba1b9d72..008f1b05a7a9 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -243,7 +243,7 @@ static struct svc_xprt *__svc_xpo_create(struct svc_xprt_class *xcl,
 	xprt = xcl->xcl_ops->xpo_create(serv, net, sap, len, flags);
 	if (IS_ERR(xprt))
 		trace_svc_xprt_create_err(serv->sv_program->pg_name,
-					  xcl->xcl_name, sap, xprt);
+					  xcl->xcl_name, sap, len, xprt);
 	return xprt;
 }