CVE-2024-39496

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

btrfs: zoned: fix use-after-free due to race with dev replace

While loading a zones info during creation of a block group, we can race with a device replace operation and then trigger a use-after-free on the device that was just replaced (source device of the replace operation).

This happens because at btrfs_load_zone_info() we extract a device from the chunk map into a local variable and then use the device while not under the protection of the device replace rwsem. So if theres a device replace operation happening when we extract the device and that device is the source of the replace operation, we will trigger a use-after-free if before we finish using the device the replace operation finishes and frees the device.

Fix this by enlarging the critical section under the protection of the device replace rwsem so that all uses of the device are done inside the critical section.

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/0090d6e1b210551e63cf43958dc7a1ec942cdde9
• https://git.kernel.org/stable/c/092571ef9a812566c8f2c9038d9c2a64c49788d6
• https://git.kernel.org/stable/c/17765964703b88d8befd899f8501150bb7e07e43
• https://git.kernel.org/stable/c/a0cc006f4214b87e70983c692e05bb36c59b5752