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From 52bf635da30c75d0fdb0a3e7e7b9a2483ca033fc Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>
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Date: Thu, 29 Jul 2021 04:55:59 -0400
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Subject: [PATCH 05/14] Add mtod_check()
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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RH-Author: Marc-André Lureau <marcandre.lureau@redhat.com>
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Message-id: <20210708082537.1550263-2-marcandre.lureau@redhat.com>
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Patchwork-id: 101819
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O-Subject: [RHEL-8.5.0 qemu-kvm PATCH 1/8] Add mtod_check()
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Bugzilla: 1970819 1970835 1970843 1970853
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RH-Acked-by: Stefano Garzarella <sgarzare@redhat.com>
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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From: Marc-André Lureau <marcandre.lureau@redhat.com>
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Recent security issues demonstrate the lack of safety care when casting
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a mbuf to a particular structure type. At least, it should check that
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the buffer is large enough. The following patches will make use of this
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function.
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Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
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(cherry picked from commit 93e645e72a056ec0b2c16e0299fc5c6b94e4ca17)
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Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 slirp/src/mbuf.c | 11 +++++++++++
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 slirp/src/mbuf.h |  1 +
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 2 files changed, 12 insertions(+)
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diff --git a/slirp/src/mbuf.c b/slirp/src/mbuf.c
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index 4fd62282a9..6d0653ed3d 100644
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--- a/slirp/src/mbuf.c
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+++ b/slirp/src/mbuf.c
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@@ -222,3 +222,14 @@ struct mbuf *dtom(Slirp *slirp, void *dat)
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     return (struct mbuf *)0;
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 }
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+
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+void *mtod_check(struct mbuf *m, size_t len)
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+{
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+    if (m->m_len >= len) {
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+        return m->m_data;
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+    }
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+
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+    DEBUG_ERROR("mtod failed");
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+
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+    return NULL;
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+}
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diff --git a/slirp/src/mbuf.h b/slirp/src/mbuf.h
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index 546e7852c5..2015e3232f 100644
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--- a/slirp/src/mbuf.h
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+++ b/slirp/src/mbuf.h
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@@ -118,6 +118,7 @@ void m_inc(struct mbuf *, int);
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 void m_adj(struct mbuf *, int);
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 int m_copy(struct mbuf *, struct mbuf *, int, int);
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 struct mbuf *dtom(Slirp *, void *);
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+void *mtod_check(struct mbuf *, size_t len);
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 static inline void ifs_init(struct mbuf *ifm)
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 {
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-- 
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2.27.0
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