CVE-2024-39495

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

greybus: Fix use-after-free bug in gb_interface_release due to race condition.

In gb_interface_create, &intf->mode_switch_completion is bound with gb_interface_mode_switch_work. Then it will be started by gb_interface_request_mode_switch. Here is the relevant code. if (!queue_work(system_long_wq, &intf->mode_switch_work)) { … }

If we call gb_interface_release to make cleanup, there may be an unfinished work. This function will call kfree to free the object intf. However, if gb_interface_mode_switch_work is scheduled to run after kfree, it may cause use-after-free error as gb_interface_mode_switch_work will use the object intf. The possible execution flow that may lead to the issue is as follows:

CPU0 CPU1

                        |   gb_interface_create
                        |   gb_interface_request_mode_switch

gb_interface_release | kfree(intf) (free) | | gb_interface_mode_switch_work | mutex_lock(&intf->mutex) (use)

Fix it by canceling the work before kfree.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/03ea2b129344152157418929f06726989efc0445
• https://git.kernel.org/stable/c/0b8fba38bdfb848fac52e71270b2aa3538c996ea
• https://git.kernel.org/stable/c/2b6bb0b4abfd79b8698ee161bb73c0936a2aaf83
• https://git.kernel.org/stable/c/5c9c5d7f26acc2c669c1dcf57d1bb43ee99220ce
• https://git.kernel.org/stable/c/74cd0a421896b2e07eafe7da4275302bfecef201
• https://git.kernel.org/stable/c/9a733d69a4a59c2d08620e6589d823c24be773dc
• https://git.kernel.org/stable/c/fb071f5c75d4b1c177824de74ee75f9dd34123b9