USB: gadget: dummy-hcd: Fix wait for outstanding request completions

Overview

In the Linux kernel, the following vulnerability has been resolved:

USB: gadget: dummy-hcd: Fix wait for outstanding request completions

The dummy-hcd driver emulates synchronize_irq() by waiting until its private callback_usage counter drops to 0 (with the private lock not held). This counter is incremented whenever a gadget driver callback occurs (which requires the private lock to be dropped), but not when a request completion handler is called.

This is an oversight. Request completion is triggered by timer interrupts (emulating device IRQs in a real UDC), and the interrupt handlers are supposed to have completed when the synchronize_irq() emulation routine returns -- they aren't supposed to be in the middle of a completion callback. If this happens it can lead to a gadget driver's unbind routine running before all outstanding request completions have finished, maybe even allowing the gadget driver's module to be unloaded while a completion handler is still running.

Fix the oversight by incrementing the callback_usage value across request completion callbacks.

Affected

• Linux >= 7dbd8f4cabd96db5a50513de9d83a8105a5ffc81 < 7ce4dca0d53b1c3cb2b7e7bb2e42bf5db860caf2
• Linux >= 7dbd8f4cabd96db5a50513de9d83a8105a5ffc81 < 5298c96bf0068f3160969f7ddad81976d01a9b66
• Linux >= 7dbd8f4cabd96db5a50513de9d83a8105a5ffc81 < 3070806a7bc7bb36ed04a21022c09dafcc5619f4
• Linux >= 7dbd8f4cabd96db5a50513de9d83a8105a5ffc81 < b263ff9b0fc5c1f371d65c4eb196b31263d039ff
• Linux 7b416b9dac6ede26d4ca0c1a88b448b543623ff3
• Linux 8590bc1da625dd4a589eac0fc3aa3cf4f400424d
• Linux a867d5b932ac4911d3f8a1e63505061b0c81f889
• Linux e84b4a008365b7edbd842a063ae28d040a98db25
• Linux e39b17143a5b5aac81f066d455e5d3a9877eb3ae
• Linux 4f8ae1fcb0dfbb72a7678f81bf01fb7fc85c6715
• Linux >= 3.2.97 < 3.3
• Linux >= 3.16.52 < 3.17
• Linux >= 4.1.46 < 4.2
• Linux >= 4.4.92 < 4.5
• Linux >= 4.9.55 < 4.10
• Linux >= 4.13.6 < 4.14
• Linux 4.14

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.