CVE-2022-50202

Description

In the Linux kernel, the following vulnerability has been resolved: PM: hibernate: defer device probing when resuming from hibernation syzbot is reporting hung task at misc_open() [1], for there is a race window of AB-BA deadlock which involves probe_count variable. Currently wait_for_device_probe() from snapshot_open() from misc_open() can sleep forever with misc_mtx held if probe_count cannot become 0. When a device is probed by hub_event() work function, probe_count is incremented before the probe function starts, and probe_count is decremented after the probe function completed. There are three cases that can prevent probe_count from dropping to 0. (a) A device being probed stopped responding (i.e. broken/malicious hardware). (b) A process emulating a USB device using /dev/raw-gadget interface stopped responding for some reason. (c) New device probe requests keeps coming in before existing device probe requests complete. The phenomenon syzbot is reporting is (b). A process which is holding system_transition_mutex and misc_mtx is waiting for probe_count to become 0 inside wait_for_device_probe(), but the probe function which is called from hub_event() work function is waiting for the processes which are blocked at mutex_lock(&misc_mtx) to respond via /dev/raw-gadget interface. This patch mitigates (b) by deferring wait_for_device_probe() from snapshot_open() to snapshot_write() and snapshot_ioctl(). Please note that the possibility of (b) remains as long as any thread which is emulating a USB device via /dev/raw-gadget interface can be blocked by uninterruptible blocking operations (e.g. mutex_lock()). Please also note that (a) and (c) are not addressed. Regarding (c), we should change the code to wait for only one device which contains the image for resuming from hibernation. I don't know how to address (a), for use of timeout for wait_for_device_probe() might result in loss of user data in the image. Maybe we should require the userland to wait for the image device before opening /dev/snapshot interface.

Gravité et risque d'exploitation

CVE-2022-50202 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.25 %, ce qui la place devant 15.0 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions c751085943362143f84346d274e0011419c84202, 0, <2f0e18e0db42f4f8bc87d3d98333680065ceeff8, <5a283b59bce72c05c60e9f0fa92a28b5b850d8bb, 4.14.291, 5.19.2, <=5.10.*, 2.6.30, <=4.14.*, <003a456ae6f70bb97e436e02fc5105be577c1570, 5.10.137, 6.0, 5.4.211, <b8e1ae9433d7bd95f2dcc044a7a6f20a4c40d258, <=5.18.*, <=5.4.*, <2.6.30, <=4.19.*, <8c90947e5f1801e6c7120021c6ea0f3ad6a4eb91, 5.15.61, 4.19.256, <f7042cf9dd40733f387b7cac021e626c74b8856f, 5.18.18, <8386c414e27caba8501119948e9551e52b527f59, <=*, <=5.15.*, <3c48d3067eaf878642276f053575a5c642600a50, <=5.19.*) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/8c90947e5f1801e6c7120021c6ea0f3ad6a4eb91
• https://git.kernel.org/stable/c/5a283b59bce72c05c60e9f0fa92a28b5b850d8bb
• https://git.kernel.org/stable/c/3c48d3067eaf878642276f053575a5c642600a50
• https://git.kernel.org/stable/c/003a456ae6f70bb97e436e02fc5105be577c1570
• https://git.kernel.org/stable/c/2f0e18e0db42f4f8bc87d3d98333680065ceeff8
• https://git.kernel.org/stable/c/b8e1ae9433d7bd95f2dcc044a7a6f20a4c40d258
• https://git.kernel.org/stable/c/f7042cf9dd40733f387b7cac021e626c74b8856f
• https://git.kernel.org/stable/c/8386c414e27caba8501119948e9551e52b527f59