CVE-2019-19770

Published: 12 December 2019

** DISPUTED ** In the Linux kernel 4.19.83, there is a use-after-free (read) in the debugfs_remove function in fs/debugfs/inode.c (which is used to remove a file or directory in debugfs that was previously created with a call to another debugfs function such as debugfs_create_file). NOTE: Linux kernel developers dispute this issue as not being an issue with debugfs, instead this is an issue with misuse of debugfs within blktrace.

From the Ubuntu security team

It was discovered that debugfs in the Linux kernel as used by blktrace contained a use-after-free in some situations. A privileged local attacker could possibly use this to cause a denial of service (system crash).

Priority

Low

CVSS 3 base score: 8.2

Status

Notes

reproducer in github link
according to kernel maintainer, needed commits are:
(1b0b28364816) blktrace: break out of blktrace setup on concurrent calls
(c3dbe541ef77) blktrace: Avoid sparse warnings when assigning q->blk_trace
(a67549c8e568) blktrace: annotate required lock on do_blk_trace_setup()
(bad8e64fb19d) blktrace: fix debugfs use after free
(b431ef837e33) blktrace: ensure our debugfs dir exists

References

• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-19770
• https://bugzilla.kernel.org/show_bug.cgi?id=205713
• https://lore.kernel.org/linux-block/20200419194529.4872-1-mcgrof@kernel.org/
• https://lore.kernel.org/linux-block/20200516031956.2605-1-mcgrof@kernel.org/
• https://github.com/mcgrof/break-blktrace
• https://ubuntu.com/security/notices/USN-4680-1
• NVD
• Launchpad
• Debian

Bugs

• https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1904471