CVE-2024-41012

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

filelock: Remove locks reliably when fcntl/close race is detected

When fcntl_setlk() races with close(), it removes the created lock with do_lock_file_wait(). However, LSMs can allow the first do_lock_file_wait() that created the lock while denying the second do_lock_file_wait() that tries to remove the lock. Separately, posix_lock_file() could also fail to remove a lock due to GFP_KERNEL allocation failure (when splitting a range in the middle).

After the bug has been triggered, use-after-free reads will occur in lock_get_status() when userspace reads /proc/locks. This can likely be used to read arbitrary kernel memory, but cant corrupt kernel memory.

Fix it by calling locks_remove_posix() instead, which is designed to reliably get rid of POSIX locks associated with the given file and files_struct and is also used by filp_flush().

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/3cad1bc010416c6dd780643476bc59ed742436b9
• https://git.kernel.org/stable/c/52c87ab18c76c14d7209646ccb3283b3f5d87b22
• https://git.kernel.org/stable/c/5661b9c7ec189406c2dde00837aaa4672efb6240
• https://git.kernel.org/stable/c/5f5d0799eb0a01d550c21b7894e26b2d9db55763
• https://git.kernel.org/stable/c/b6d223942c34057fdfd8f149e763fa823731b224
• https://git.kernel.org/stable/c/d30ff33040834c3b9eee29740acd92f9c7ba2250
• https://git.kernel.org/stable/c/dc2ce1dfceaa0767211a9d963ddb029ab21c4235
• https://git.kernel.org/stable/c/ef8fc41cd6f95f9a4a3470f085aecf350569a0b3