Mailinglist Archive: opensuse-factory (602 mails)

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Re: [opensuse-factory] Re: [PLEASE SPEAK UP] Disabling legacy file systems by default?
On Fri, 2019-02-01 at 12:48 +0100, Stefan Seyfried wrote:
Am 01.02.19 um 12:40 schrieb Michal Suchánek:
On Fri, 1 Feb 2019 10:55:59 +0100
Stefan Seyfried <stefan.seyfried@xxxxxxxxxxxxxx> wrote:
Am 01.02.19 um 10:36 schrieb Andrei Borzenkov:
modprobe --ignore-install

Yes, but that is no longer "just load it manually" but "load it
manually with special options".
Which is easy, simple and logical for you and me, but maybe not
for "Joe User" :-)

If the message or the blacklist file says so it is very logical.

even better:
vbox-seife:~ # cat /etc/modprobe.d/99-jfs.conf
install jfs logger -t modprobe "jfs logmessage"; echo "JFS disabled
by blacklist.conf, use --ignore-install"
vbox-seife:~ # modprobe jfs
JFS disabled by blacklist.conf, use --ignore-install
vbox-seife:~ # tail -1 /var/log/messages
20190201-12:46:01.8 modprobe: jfs logmessage

So we could log to syslog and to the terminal for interactive use.

Thanks for the suggestion, but sorry, I don't like that. "blacklist" is
neat and clean. "install" opens up a can of worms. Look at the man
page of modprobe.d: "install" is essentially deprecated.

More issues with that suggestion:

- The "echo" command is not printed to the console for users running
mount(8); only users running modprobe see it.

- With the "blacklist" approach, you can work around the problem with
a plain "modprobe jfs". With the "install" approach, you now need to
run "modprobe --ignore-install jfs".

- It hasn't been the intention to prohibit "modprobe jfs". On the
contrary, we explicitly allow / encourage users to do that to work
around the blacklist entries if they need to.

- generating or modifying (possibly arbitrary) "install" directives
is significantly more complex then handling simple "blacklist"
entries in %post. Well - I guess it comes down to commenting out,
but we'd need to think it through thoroughly.

I've proposed a log message printed by libmount when the ENODEV error
is encountered in the blacklisting approach. The message looks like

# mount /tmp/cramfs-img /mnt/img
mount: /mnt/img: unknown filesystem type 'cramfs' (hint: possibly blacklisted,
see mount(8)).

(the first part is the standard message, the "hint" is appended if one
of our "blacklist candidates" is encountered).
I *think* this message would show up in the journal for GUI users.
(not sure where, though).

The man page then contains a paragraph about blacklisted file systems:

Blacklisted file systems
In the Linux kernel, file system types are implemented as kernel
modules. While many of these file systems are well main-
tained, some of the older and less frequently used ones are not.
This poses a security risk, because maliciously crafted
file system images might open security holes when mounted either
automatically or by an inadvertent user. The mount command
prints "unsupported file system type 'somefs'" in this case, because it
can't distinguish between a really unsupported file
system (kernel module non-existent) and a blacklisted file system.

Users who need the blacklisted file systems and therefore want to
override the blacklisting can either load the blacklisted
module directly:

modprobe -v somefs

or override the blacklist configuration by editing files under the
/etc/modprobe.d directory.


Dr. Martin Wilck <mwilck@xxxxxxxx>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)

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