linux-kernel - [PATCH 4.7 185/186] Documentation/module-signing.txt: Note need for version info if reusing a key

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Date:	Thu, 18 Aug 2016 16:00:02 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Ben Hutchings <ben@...adent.org.uk>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: [PATCH 4.7 185/186] Documentation/module-signing.txt: Note need for version info if reusing a key

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@...adent.org.uk>

commit b8612e517c3c9809e1200b72c474dbfd969e5a83 upstream.

Signing a module should only make it trusted by the specific kernel it
was built for, not anything else.  If a module signing key is used for
multiple ABI-incompatible kernels, the modules need to include enough
version information to distinguish them.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 Documentation/module-signing.txt |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/Documentation/module-signing.txt
+++ b/Documentation/module-signing.txt
@@ -271,3 +271,9 @@ Since the private key is used to sign mo
 the private key to sign modules and compromise the operating system.  The
 private key must be either destroyed or moved to a secure location and not kept
 in the root node of the kernel source tree.
+
+If you use the same private key to sign modules for multiple kernel
+configurations, you must ensure that the module version information is
+sufficient to prevent loading a module into a different kernel.  Either
+set CONFIG_MODVERSIONS=y or ensure that each configuration has a different
+kernel release string by changing EXTRAVERSION or CONFIG_LOCALVERSION.