File 0397-libslirp-Add-mtod_check.patch of Package qemu.29142

From: Jose R Ziviani <jose.ziviani@suse.com>
Date: Tue, 6 Jul 2021 16:54:19 -0600
Subject: libslirp: Add mtod_check()
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Git-commit: 93e645e72a056ec0b2c16e0299fc5c6b94e4ca17
References: bsc#1187364, CVE-2021-3592
            bsc#1187367, CVE-2021-3594

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>
Signed-off-by: Jose R Ziviani <jose.ziviani@suse.com>
---
 slirp/mbuf.c | 11 +++++++++++
 slirp/mbuf.h |  1 +
 2 files changed, 12 insertions(+)

diff --git a/slirp/mbuf.c b/slirp/mbuf.c
index 65b26db5d874e1205ceda9bebc3c..72c2f3dc4f6059073b32315ca4d6 100644
--- a/slirp/mbuf.c
+++ b/slirp/mbuf.c
@@ -240,3 +240,14 @@ 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/slirp/mbuf.h b/slirp/mbuf.h
index 00a473b9d277b3f745fbd089b6b3..24eafdb30470efa6ed85ce90981e 100644
--- a/slirp/mbuf.h
+++ b/slirp/mbuf.h
@@ -105,6 +105,7 @@ 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)
 {