From 8f130c9462750f2ec8205b0749ecd64b799144b5 Mon Sep 17 00:00:00 2001

From: jmaloy <jmaloy@redhat.com>

Date: Wed, 19 Feb 2020 16:29:22 +0100

Subject: [PATCH 1/2] util: add slirp_fmt() helpers

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Message-id: <20200219162923.18327-2-jmaloy@redhat.com>

Patchwork-id: 93976

O-Subject: [RHEL-7.8 qemu-kvm-rhev PATCH v2 1/2] util: add slirp_fmt() helpers

Bugzilla: 1798974

RH-Acked-by: Maxim Levitsky <mlevitsk@redhat.com>

RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

RH-Acked-by: Eduardo Habkost <ehabkost@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)

Manually re-adapted, since there is no util.c file in this code version.

We add the two functions as static functions in the file where they

are going to be used.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>

Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>

---

 slirp/tcp_subr.c | 65 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 1 file changed, 65 insertions(+)

diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c

index b95ba23..c5196a4 100644

--- a/slirp/tcp_subr.c

+++ b/slirp/tcp_subr.c

@@ -45,6 +45,9 @@

 /* Don't do rfc1323 performance enhancements */

 #define TCP_DO_RFC1323 0

+static int slirp_fmt(char *str, size_t size, const char *format, ...);

+static int slirp_fmt0(char *str, size_t size, const char *format, ...);

+

 /*

  * Tcp initialization

  */

@@ -990,3 +993,65 @@ int tcp_ctl(struct socket *so)

     sb->sb_wptr += sb->sb_cc;

     return 0;

 }

+

+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

+ */

+static 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

+ */

+static 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;

+}

-- 

1.8.3.1