CVE-2019-5612

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 ============================================================================= FreeBSD-SA-19:23.midi Security Advisory The FreeBSD Project Topic: kernel memory disclosure from /dev/midistat Category: core Module: sound Announced: 2019-08-20 Credits: Peter Holm, Mark Johnston Affects: All supported versions of FreeBSD. Corrected: 2019-08-20 17:53:16 UTC (stable/12, 12.0-STABLE) 2019-08-20 17:50:33 UTC (releng/12.0, 12.0-RELEASE-p10) 2019-08-20 17:54:18 UTC (stable/11, 11.3-STABLE) 2019-08-20 17:50:33 UTC (releng/11.3, 11.3-RELEASE-p3) 2019-08-20 17:50:33 UTC (releng/11.2, 11.2-RELEASE-p14) CVE Name: CVE-2019-5612 For general information regarding FreeBSD Security Advisories, including descriptions of the fields above, security branches, and the following sections, please visit . 0. Revision history v1.0 2019-08-20 Initial release. v1.1 2019-08-21 Updated workaround. I. Background /dev/midistat is a device file which can be read to obtain a human-readable list of the available MIDI-capable devices in the system. II. Problem Description The kernel driver for /dev/midistat implements a handler for read(2). This handler is not thread-safe, and a multi-threaded program can exploit races in the handler to cause it to copy out kernel memory outside the boundaries of midistat’s data buffer. III. Impact The races allow a program to read kernel memory within a 4GB window centered at midistat’s data buffer. The buffer is allocated each time the device is opened, so an attacker is not limited to a static 4GB region of memory. On 32-bit platforms, an attempt to trigger the race may cause a page fault in kernel mode, leading to a panic. IV. Workaround Restrict permissions on /dev/midistat by adding an entry to /etc/devfs.conf and restarting the service: # echo “perm midistat 0600” >> /etc/devfs.conf # service devfs restart Custom kernels without “device sound” are not vulnerable. V. Solution Upgrade your vulnerable system to a supported FreeBSD stable or release / security branch (releng) dated after the correction date, and reboot. 1) To update your vulnerable system via a binary patch: Systems running a RELEASE version of FreeBSD on the i386 or amd64 platforms can be updated via the freebsd-update(8) utility: # freebsd-update fetch # freebsd-update install # shutdown -r +10min “Rebooting for security update” 2) To update your vulnerable system via a source code patch: The following patches have been verified to apply to the applicable FreeBSD release branches. a) Download the relevant patch from the location below, and verify the detached PGP signature using your PGP utility. # fetch https://security.FreeBSD.org/patches/SA-19:23/midi.patch # fetch https://security.FreeBSD.org/patches/SA-19:23/midi.patch.asc # gpg --verify midi.patch.asc b) Apply the patch. Execute the following commands as root: # cd /usr/src # patch < /path/to/patch c) Recompile your kernel as described in and reboot the system. VI. Correction details The following list contains the correction revision numbers for each affected branch. Branch/path Revision - ------------------------------------------------------------------------- stable/12/ r351264 releng/12.0/ r351260 stable/11/ r351265 releng/11.3/ r351260 releng/11.2/ r351260 - ------------------------------------------------------------------------- To see which files were modified by a particular revision, run the following command, replacing NNNNNN with the revision number, on a machine with Subversion installed: # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base Or visit the following URL, replacing NNNNNN with the revision number: VII. References The latest revision of this advisory is available at -----BEGIN PGP SIGNATURE----- iQKTBAEBCgB9FiEE/A6HiuWv54gCjWNV05eS9J6n5cIFAl1d58xfFIAAAAAALgAo aXNzdWVyLWZwckBub3RhdGlvbnMub3BlbnBncC5maWZ0aGhvcnNlbWFuLm5ldEZD MEU4NzhBRTVBRkU3ODgwMjhENjM1NUQzOTc5MkY0OUVBN0U1QzIACgkQ05eS9J6n 5cJ3pw//fbHMCysvmMh+2RZ47d4i9d61cdYEq51VUwT2Cp2pGz+mWAoac89c4k2v coo+nuvsXfgNGjr6SHGjLw0kCjeJPdPBDstHLnrzqbmuUFeS8rbRS9AGySy8cW7Z qYh8OuBPqczWRM2STtyIA1nuxrKBxpEKsWdCO41lTue/D6+1rPjFkRtzK5G/yNcJ 2gQjy8DKwX2RdUmjrWXoQbGheCKUz+euhkUOFHjiJYAdLAK4Bq+Dn/Nq36c6Dej0 wzYkeDwL+c/XxVPk1iucMJfDd+xrOi6HY4BLh4EFkJBKmQa6ciqa1B37ibARMtVb QbGcjgoUQ1wJLxJEpD0JN5/Rbxg3KOq+8wH5if2pqW8Q9Ir89GNpbq2DjNVpBq28 1XEE0CpIJUsqZkSobkMlmwQkz4fYNm5PGkIxpVGAUUlhEpnPlHsIWX5ADhyUwS8y qGkYWDrB7t5kn+66pwef6HOQdSA+76MdHzsb9NF+5ByvcgSqgEJqVpFs31+hAfTQ fH+UefOm7E65GEARG8M2NUUQnMDY/GlXOaeVgbUu60FPbr3M3QlTuAZcBZZTwd+f aDtQt4J2P33qfkJWoH4Lt5qNzcGkucFQliKZ0SI4W0IfpaqWlRTaUcaC6MZClgdN hh/cTP3WruHVsgQKPPO1F1soFCP96cDI1LVeHiYYTLBX0n5JarQ= =AI8Q -----END PGP SIGNATURE-----