[PATCH v2 04/14] docs: threat-model: clarify the case of automatically mounted file systems

[Willy Tarreau <w@1wt.eu>]

Bugs triggered by crafted file system images are among the most
frequently reported non-security issues, often with the argument that
some desktop environments automatically mount removable media without
checking them.

Let's state that automatic mounting of unchecked file systems does not
change the analysis: an automounter is expected to check a file system
before mounting it, otherwise it is at fault, and if the check does not
detect the issue, the file system checker is at fault (this doesn't void
the need to handle the kernel side of the report). Fixes should then be
directed to these tools. The only exception remains drivers specifically
documented as being hardened against hostile inputs, as already stated
for non-conforming devices and media.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 Documentation/process/threat-model.rst | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/Documentation/process/threat-model.rst b/Documentation/process/threat-model.rst
index 4c61f196fa84d..a55e7c1c11968 100644
--- a/Documentation/process/threat-model.rst
+++ b/Documentation/process/threat-model.rst
@@ -234,7 +234,12 @@ The following classes of problems are not considered vulnerabilities:
     image: mounting a block device is a privileged operation (see above), and
     the administrator is responsible for the media they mount. This includes
     issues that are resolved, mitigated, or detected by running a filesystem
-    consistency check (fsck) on the image prior to mounting.
+    consistency check (fsck) on the image prior to mounting. Automatic
+    mounting of unchecked file systems (e.g. removable media mounted by a
+    desktop environment) does not change this: an automounter is expected to
+    check a file system before mounting it, otherwise it is at fault, and if
+    the check does not detect the issue, the file system checker is at fault.
+    In such cases, fixes should be directed to these tools.
 
   * bugs whose reproduction requires hardware modification or emulation,
     including fake USB devices that pretend to be another one, or devices
-- 
2.52.0