From 87f5d0c70bdb46d467d32e3c3a8d7a472c97e148 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
Date: Fri, 4 Jun 2021 15:58:25 +0400
Subject: [PATCH 1/7] Add mtod_check()
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Recent security issues demonstrate the lack of safety care when casting
a mbuf to a particular structure type. At least, it should check that
the buffer is large enough. The following patches will make use of this
function.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
(cherry picked from commit 93e645e72a056ec0b2c16e0299fc5c6b94e4ca17)
---
 src/mbuf.c | 11 +++++++++++
 src/mbuf.h |  1 +
 2 files changed, 12 insertions(+)

diff --git a/src/mbuf.c b/src/mbuf.c
index 54ec721..cb2e971 100644
--- a/src/mbuf.c
+++ b/src/mbuf.c
@@ -222,3 +222,14 @@ struct mbuf *dtom(Slirp *slirp, void *dat)
 
     return (struct mbuf *)0;
 }
+
+void *mtod_check(struct mbuf *m, size_t len)
+{
+    if (m->m_len >= len) {
+        return m->m_data;
+    }
+
+    DEBUG_ERROR("mtod failed");
+
+    return NULL;
+}
diff --git a/src/mbuf.h b/src/mbuf.h
index 546e785..2015e32 100644
--- a/src/mbuf.h
+++ b/src/mbuf.h
@@ -118,6 +118,7 @@ void m_inc(struct mbuf *, int);
 void m_adj(struct mbuf *, int);
 int m_copy(struct mbuf *, struct mbuf *, int, int);
 struct mbuf *dtom(Slirp *, void *);
+void *mtod_check(struct mbuf *, size_t len);
 
 static inline void ifs_init(struct mbuf *ifm)
 {
-- 
2.29.0