From e30250c95b840896da4cb71e84bead5803ee1ff6 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 16 Dec 2016 13:42:06 -0500
Subject: [PATCH] sg_write()/bsg_write() is not fit to be called under
 KERNEL_DS

commit a0ac402cfcdc904f9772e1762b3fda112dcc56a0 upstream.

Both damn things interpret userland pointers embedded into the payload;
worse, they are actually traversing those.  Leaving aside the bad
API design, this is very much _not_ safe to call with KERNEL_DS.
Bail out early if that happens.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
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