From 2a4ee2d1702febccc0d81c1724eb61cb654ed72f Mon Sep 17 00:00:00 2001
From: jmaloy <jmaloy@redhat.com>
Date: Thu, 14 May 2020 21:13:09 +0100
Subject: [PATCH 1/6] util: add slirp_fmt() helpers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

RH-Author: jmaloy <jmaloy@redhat.com>
Message-id: <20200514211314.1534001-2-jmaloy@redhat.com>
Patchwork-id: 96585
O-Subject: [RHEL-8.2.0 qemu-kvm PATCH v2 1/6] util: add slirp_fmt() helpers
Bugzilla: 1834477
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
RH-Acked-by: Kevin Wolf <kwolf@redhat.com>

From: Marc-André Lureau <marcandre.lureau@redhat.com>

Various calls to snprintf() in libslirp assume that snprintf() returns
"only" the number of bytes written (excluding terminating NUL).

https://pubs.opengroup.org/onlinepubs/9699919799/functions/snprintf.html#tag_16_159_04

"Upon successful completion, the snprintf() function shall return the
number of bytes that would be written to s had n been sufficiently
large excluding the terminating null byte."

Introduce slirp_fmt() that handles several pathological cases the
way libslirp usually expect:

- treat error as fatal (instead of silently returning -1)

- fmt0() will always \0 end

- return the number of bytes actually written (instead of what would
  have been written, which would usually result in OOB later), including
  the ending \0 for fmt0()

- warn if truncation happened (instead of ignoring)

  Other less common cases can still be handled with strcpy/snprintf() etc.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20200127092414.169796-2-marcandre.lureau@redhat.com>

(cherry-picked from libslirp commit 30648c03b27fb8d9611b723184216cd3174b6775)
Manual cherry pick, since there is no util.c file in this code version.
Instead, we add the new functions to the file misc.c.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>
---
 slirp/misc.c  | 62 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 slirp/slirp.h |  2 ++
 2 files changed, 64 insertions(+)

diff --git a/slirp/misc.c b/slirp/misc.c
index 260187b..035b9ab 100644
--- a/slirp/misc.c
+++ b/slirp/misc.c
@@ -293,3 +293,65 @@ void slirp_connection_info(Slirp *slirp, Monitor *mon)
                        so->so_rcv.sb_cc, so->so_snd.sb_cc);
     }
 }
+
+static int slirp_vsnprintf(char *str, size_t size,
+                           const char *format, va_list args)
+{
+    int rv = vsnprintf(str, size, format, args);
+
+    if (rv < 0) {
+        g_error("vsnprintf() failed: %s", g_strerror(errno));
+    }
+
+    return rv;
+}
+
+/*
+ * A snprintf()-like function that:
+ * - returns the number of bytes written (excluding optional \0-ending)
+ * - dies on error
+ * - warn on truncation
+ */
+int slirp_fmt(char *str, size_t size, const char *format, ...)
+{
+    va_list args;
+    int rv;
+
+    va_start(args, format);
+    rv = slirp_vsnprintf(str, size, format, args);
+    va_end(args);
+
+    if (rv > size) {
+        g_critical("vsnprintf() truncation");
+    }
+
+    return MIN(rv, size);
+}
+
+/*
+ * A snprintf()-like function that:
+ * - always \0-end (unless size == 0)
+ * - returns the number of bytes actually written, including \0 ending
+ * - dies on error
+ * - warn on truncation
+ */
+int slirp_fmt0(char *str, size_t size, const char *format, ...)
+{
+    va_list args;
+    int rv;
+
+    va_start(args, format);
+    rv = slirp_vsnprintf(str, size, format, args);
+    va_end(args);
+
+    if (rv >= size) {
+        g_critical("vsnprintf() truncation");
+        if (size > 0)
+            str[size - 1] = '\0';
+        rv = size;
+    } else {
+        rv += 1; /* include \0 */
+    }
+
+    return rv;
+}
diff --git a/slirp/slirp.h b/slirp/slirp.h
index 06febfc..49b8c2c 100644
--- a/slirp/slirp.h
+++ b/slirp/slirp.h
@@ -292,5 +292,7 @@ uint8_t tcp_tos(struct socket *);
 int tcp_emu(struct socket *, struct mbuf *);
 int tcp_ctl(struct socket *);
 struct tcpcb *tcp_drop(struct tcpcb *tp, int err);
+int slirp_fmt(char *str, size_t size, const char *format, ...);
+int slirp_fmt0(char *str, size_t size, const char *format, ...);
 
 #endif
-- 
1.8.3.1