CVE-2022-49085

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

drbd: Fix five use after free bugs in get_initial_state

In get_initial_state, it calls notify_initial_state_done(skb,..) if cb->args[5]==1. If genlmsg_put() failed in notify_initial_state_done(), the skb will be freed by nlmsg_free(skb). Then get_initial_state will goto out and the freed skb will be used by return value skb->len, which is a uaf bug.

Whats worse, the same problem goes even further: skb can also be freed in the notify_state_change -> notify_state calls below. Thus 4 additional uaf bugs happened.

My patch lets the problem callee functions: notify_initial_state_done and notify_*_state_change return an error code if errors happen. So that the error codes could be propagated and the uaf bugs can be avoid.

v2 reports a compilation warning. This v3 fixed this warning and built successfully in my local environment with no additional warnings. v2: https://lore.kernel.org/patchwork/patch/1435218/

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/0489700bfeb1e53eb2039c2291c67e71b0b40103
• https://git.kernel.org/stable/c/188fe6b26765edbad4055611c0f788b6870f4024
• https://git.kernel.org/stable/c/226e993c39405292781bfcf4b039a8db56aab362
• https://git.kernel.org/stable/c/594205b4936771a250f9d141e7e0fff21c3dd2d9
• https://git.kernel.org/stable/c/a972c768723359ec995579902473028fe3cd64b1
• https://git.kernel.org/stable/c/aadb22ba2f656581b2f733deb3a467c48cc618f6
• https://git.kernel.org/stable/c/b6a4055036eed1f5e239ce3d8b0db1ce38bba447
• https://git.kernel.org/stable/c/dcf6be17b5c53b741898d2223b23e66d682de300
• https://git.kernel.org/stable/c/de63e74da2333b4068bb79983e632db730fea97e