CVE-2021-47334

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

misc/libmasm/module: Fix two use after free in ibmasm_init_one

In ibmasm_init_one, it calls ibmasm_init_remote_input_dev(). Inside ibmasm_init_remote_input_dev, mouse_dev and keybd_dev are allocated by input_allocate_device(), and assigned to sp->remote.mouse_dev and sp->remote.keybd_dev respectively.

In the err_free_devices error branch of ibmasm_init_one, mouse_dev and keybd_dev are freed by input_free_device(), and return error. Then the execution runs into error_send_message error branch of ibmasm_init_one, where ibmasm_free_remote_input_dev(sp) is called to unregister the freed sp->remote.mouse_dev and sp->remote.keybd_dev.

My patch add a error_init_remote label to handle the error of ibmasm_init_remote_input_dev(), to avoid the uaf bugs.

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/1512e7dc5eb08b7d92a12e2bfcd9cb8c4a1ec069
• https://git.kernel.org/stable/c/29ba8e2ba89ee2862a26d91204dd5fe77ceee25a
• https://git.kernel.org/stable/c/38660031e80eaa6cc9370b031c180612f414b00d
• https://git.kernel.org/stable/c/481a76d4749ee3a27f902ba213fdcbb4bb39720e
• https://git.kernel.org/stable/c/5b06ca113bf197aab2ab61288f42506e0049fbab
• https://git.kernel.org/stable/c/7272b591c4cb9327c43443f67b8fbae7657dd9ae
• https://git.kernel.org/stable/c/a7268e8a227d5a4f0bd1584f556246b0224ab274
• https://git.kernel.org/stable/c/b9c87ce3bc6331f82811a8cf8e930423c22523a3
• https://git.kernel.org/stable/c/ef1067d2baa847d53c9988510d99fb494de4d12c
• https://git.kernel.org/stable/c/1512e7dc5eb08b7d92a12e2bfcd9cb8c4a1ec069
• https://git.kernel.org/stable/c/29ba8e2ba89ee2862a26d91204dd5fe77ceee25a
• https://git.kernel.org/stable/c/38660031e80eaa6cc9370b031c180612f414b00d
• https://git.kernel.org/stable/c/481a76d4749ee3a27f902ba213fdcbb4bb39720e
• https://git.kernel.org/stable/c/5b06ca113bf197aab2ab61288f42506e0049fbab
• https://git.kernel.org/stable/c/7272b591c4cb9327c43443f67b8fbae7657dd9ae
• https://git.kernel.org/stable/c/a7268e8a227d5a4f0bd1584f556246b0224ab274
• https://git.kernel.org/stable/c/b9c87ce3bc6331f82811a8cf8e930423c22523a3
• https://git.kernel.org/stable/c/ef1067d2baa847d53c9988510d99fb494de4d12c